Second Generation Legacy Turbo FAQ

[broknindarkagain]

I've seen and answered countless questions about turbo charging the second generation Subaru Legacy. I'm putting together this FAQ to help clear up some of these questions.

 

If I have missed anything, please feel free to suggest something for me to add to this FAQ. I will edit it as I see fit.

 

 

 

Can I turbo charge my Legacy?

Short answer is no, you can not. However, keep reading and I will explain ways that you are able to have boost in your car.

 

 

Why can't I turbo charge my car?

I can go on for days explaining this. However I'll try to keep it short and to the point. The EJ25D is an open deck engine. It is NOT a strong engine and does not handle boost well. There have been people who have been able to run about 4 - 5psi on them though. This is typical for a TD04 turbo, and to be honest isn't enough power for the money you will spend doing it. The EJ22E is a little bit of a stronger engine and can handle about 10psi, however the money thing comes into play here as well. You can do a swap for just a little more then it will cost you to boost your EJ22E and have considerably more power.

 

 

What about the JDM second generation Legacys? They are twin turbo!

Unlike our USDM Legacys, the JDM Subaru Legacy has an engine designed to withstand the extra power of the turbos. The EJ20R has forged internals, and VERY good heads...

 

 

I've seen Legacys online that have a turbo. How did they do it?

Most people do some kind of WRX or STI swap. This includes just about all of the WRX / STI guts. Engine, transmission, rear diff, ecu, wiring, subframe, etc. I'll go into more details later on.

 

 

What other options do I have besides a WRX or STI swap?

There are a few other options out there. Most of the JDM drivetrains can be bought on Ebay for a reasonable price. Personally, I'm running an EJ20R setup with a stand alone ECU. You can also use the older USDM Turbo Legacy engines.

 

 

What about my transmission?

The 4EAT and the 5MT are not strong transmissions. They do excellent under stock horsepower, but when you start adding the power of forced induction to them...they don't last for very long. They may work for a little while, but they will have severe problems A LOT sooner then then should.

 

 

So if my transmission isn't strong enough, what should I do?

The easiest thing to do is to find a wrecked donor car. Or you can find a transmission / rear diff combo online. I'm currently running a JDM STI v3 5 speed with a stage 1 clutch. Its good up until about 400awhp.

 

 

What about my exhaust? I've installed a turbo engine and I can't make the exhaust fit around the subframe. It looks like I have to cut part of it out!

Our stock subframes were not designed to accomadate for the turbo exhaust. The work around for this is to either use an 04 STI or any 02-07 WRX subframe. DO NOT cut your stock subframe. It will not be as strong as it needs to be if you do this. You can also run any of the USDM turbo Legacy subframes.

 

 

So can you just give me a quick list of the parts I need to do a turbo swap?

This depends on what route you go. If you do a WRX / STI swap, you will need the following

 

• Engine
  
  
• Transmission
  
  
• ECU
  
  
• Wiring
  
  
• Rear Diff
  
  
• Turbo
  
  
• Exhaust
  
  
• Subframe
  
  
• Custom Driveshaft
  
  

 

If you do some kind of JDM swap, you will need all the same stuff listed, except you will not be able to run a stock ECU. With a JDM swap, your best bet is a stand alone ecu system like AEM or Megasquirt. Piggyback systems are an option, but are more trouble then its worth.

 

 

So I did a JDM swap with a stand alone ECU, but my car doesn't run right. What do I do?

You need to get your car dyno tuned at this point. Every ECU has parameters and settings for the engine to run within. With any kind of stand alone ECU, you have to "tune" these settings to your specific setup. Its not hard to do, its just hard to get it right. If you screw up when you do it, it will cost you your engine. If you really did a swap and didn't know the answer to this, you should probably build model cars instead.

 

 

I want to do a swap, but I'm concerned about my stock axles. Will they be able to handle the extra power of a turbo engine?

You should be fine within reason. You're not going to be able to put 500awhp to stock axles, but the 200awhp area is fine on stock Legacy axles. A decent upgrade is STI or WRX axles. They are able to handle a little more abuse then the Legacy parts.

 

 

I want the EJ20R twin turbo JDM engine in my car! It will bolt right up....right?

Wrong. Its VERY difficult to run the twin turbo setup on our USDM Legacys. The reason for this is the difference between right and left hand drive. Our steering linkage, brake booster, etc gets in the way of the second turbo. I have seen a USDM Impreza run the twin turbo EJ20R, but they had to heavily modify it. My personal EJ20R has been converted to a single rotated turbo. I HIGHLY recommend the EJ20R because its an excellent engine, but expect to NOT have a twin turbo system with it.

 

 

So whats the hardest part about doing a turbo swap?

The wiring in our cars is a nightmare. If you do a WRX / STI swap with the WRX / STI ECU, you have to "splice" the stock Legacy wiring harness, and the WRX harness together. If you run a stand alone ECU, you will have to make a custom wiring harness. Trust me, there are A LOT of wires.

 

 

I chose to do a WRX / STI swap, but I want a little more power out of the stock WRX / STI drivetrain. What can I do?

Before you start upgrading the stock WRX / STI setup, you should look into some kind of piggyback system like a CobbAP. This way, you're able to tune your car to whatever mods you have installed and get all the power out of it. After a piggyback, you can do a rotated turbo setup with something bigger then the TD04 or VF39. Bigger injectors, exhaust, MSD, boost controller, etc are all good upgrades.

 

 

I always look on my local Craigslist classifieds for a wrecked WRX / STI, but I never see one. Where can I find one at?

The best places to look are local Subaru forums, NASIOC, and car auctions.

 

 

I want to use X block with X heads for my turbo build. Can I do this?

YES! This is whats known as a "hybrid" build. Usually, you can pair any EJ series head with any EJ series engine. I would recommend using ARP head studs if you plan on running a lot of boost.

 

 

I'm going to install a WRX engine, but I want to use the STI 6 speed transmission. Is this possible?

Yes it is. Just like the heads, you can mix-match engines/transmissions. Transmission mounts may be different for each transmission however. The STI 6 speed has the DCCD that will need to be wired in though, and I'm not sure how to do it...but I do know that it has been done on our cars.

 

 

Can I use my stock Legacy clutch?

Probably. I would suggest otherwise though. It will likely shatter on launch or slip under power.

 

 

What about gas mileage after a turbo swap?

Your gas mileage will suffer some. I know our cars are not the most fuel efficient cars on the road already....but any time you add more power to a vehicle, it gets worse gas mileage. My Legacy turbo isn't THAT bad on gas. The worst part of is is that I have to run 93 octane.

 

 

What else do you suggest?

I suggest some suspension and brake work to be done with your swap. If you're anything like I am, you take advantage of the AWD system and haul *ss through the corners. Now that you have more power under the hood, you're going to be able to come into these corners a lot faster. Better suspension and better brakes are a MUST. I have WRX brakes and D2 Racing coilovers. I'm pretty happy with the suspension, however I am wanting to upgrade the brakes even more so then they already are.

 

 

What is your current turbo setup?

I have a 1995 Subaru Legacy L. It has the JDM EJ20R engine in it paired with the JDM STI v3 5 speed and a limited slip rear diff. I have a Megasquirt stand alone ecu, port/polished heads, 252 cams, upgraded fuel pump, MSD, 660 injectors, front mount intercooler, rotated TD04, full 3 inch turbo-back exhaust, etc. I'm happy with my current setup, but its only good up until about 400awhp.

 

 

There isn't much space under my hood. Are you sure all this turbo stuff will fit?

Yes it will fit

http://img.photobucket.com/albums/v287/broknindarkagain/LegacySTI/199555_10150150413543326_605068325_6516934_7951161_n.jpg

 

 

 

Mechanically, you can bolt up any EJ series engine to any EJ series transmission, and drop the two into any car that was designed with any EJ series engine.

 

The exception to this EJ series engine rule is the EJ20R (JDM twin turbo). This mechanically would bolt up, but it was never available in the united states, and therefore the way the turbos are routed makes it impossible to install and have it clear the steering rack on a left hand drive car.

 

This is true, however you can use the EJ20R on left hand drive Subarus if you convert it to a single turbo setup. This will require using any stock or aftermarket WRX exhaust. The twin turbo setup does not fit around our left hand drive steering rack and linkage. It can be made to work with heavy custom modifications though, but doesn't seem to be worth the trouble.

 

 

The following is a list of Subaru EJ Turbo Charged engines that are able to fit into the second generation Legacy / Outback / Impreza

 

2.0L Single Turbo

-

EJ20G

JDM 93-96 STI, WRX 92-96

-

EJ20K

JDM 97-99 STI

-

EJ205

JDM 99-01 WRX Wagon, 01-11 WRX, USDM 02-05 WRX

-

EJ207

JDM 98-11 STI

 

2.0L Twin Turbo must be converted to single turbo

-

EJ20H

JDM 93-98 Legacy

-

EJ20R

JDM 96-98 Legacy

-

EJ206

JDM 98-03 Legacy

-

EJ208

JDM 98-03 Legacy

 

2.2L Single Turbo

-

EJ22T

USDM 90-94 Legacy

-

EJ22G

JDM Impreza STI GC8

 

2.5L Single Turbo

-

EJ255

USDM 06-11 Impreza, 04-11 Forester, 03-11 Legacy, 04-06 Baja

-

EJ257

USDM 04-11 STI

 

 

 

- If you turbo your existing engine, it'll probably break.

 

- If you turbo your existing engine, it'll probably be slow.

 

- If you plan on doing a full swap, just buy a rolled STi. The end result will be much cleaner, much more reliable, much more durable, and much faster than any piecemeal hodgepodge you put together otherwise. If you REALLY want to have a turbo second-gen that you could actually consider marginally reliable, this is pretty much the best way to go.

 

- If you DO plan on doing a WRX swap (EJ20 from a USDM donor), set aside funds to replace the EJ20 short block. Stock EJ20 heads on a stock STi shortblock with an 18G is a simple recipe for TONS of torque and lots of fun.

 

- If you are going to do it, don't skimp. You'll regret every corner you cut when the car breaks down.

 

 

EDIT :

 

If you're needing the FSM - look here http://www.sl-i.net/FORUM/viewtopic.php?f=14&t=20753

[broknindarkagain]

I have copied this from NASIOC. Its specific to the WRX / STI, however most people who do swaps in our cars will be using a WRX / STI swap. A lot of the information crosses over to other engines as well.

 

NOTE

Any mention of "open source tuning" aka RomRaider or the likes does not apply unless you run a WRX or STI ECU. If you plan on running a stock Legacy ECU, open source tuning will NOT work.

 

 

Engine Management FAQ

 

Why do I need engine management? Consider your stock engine management for just a moment. Your stock engine control unit (ECU) is a very complex piece of circuitry that calculates hundreds of variables every second. All of these variables rely on inputs within a + or – range. When you modify your vehicle, these values change. As long as the changes are within the values the ECU expects to receive, your engine runs fine. Once the values are exceeded, the ECU is programmed to compensate to return the values to normal levels.

 

This is a layman’s explanation of how your stock ECU can actually work against you when modifying your vehicle. This also explains why modifications can feel great once they are bolted on but the butt dyno results seem to fade over time. This is due to ECU compensation.

 

What is the first step in finding what engine management I need? Finding a tuner. The Tuner FAQ will help with the general rules of finding a good tuner. Remember, it's always better to have a custom tune vs. a plug and play or "staged" map. Always defer to the tuner's advice as to what to choose as ultimately he will be the one to provide custom support. Discuss your goals and budget and your tuner should set you on the right path. If you are a "plug and play" kind of person, review the options below and decide for yourself along with input from locals in your regional forum and the car parts review forum.

 

What will engine management do for me? Generally speaking, engine management optimizes several engine functions to create more horsepower and efficiency. The stock ECU is designed to ensure your car runs fine and monitors the engine’s output parameters. Utilizing an aftermarket engine management solution takes this to the next level.

 

Often times, car manufacturers will program the stock ECU with a known amount of “play”. This amount of play allows the manufacturer an extra level of safety and/or the ability to utilize this at a later date so they can have an increase in HP in later years. An example of this is where a 2001 car has 200HP and a 2002 car has 215HP. Some manufacturers couple this with additional parts to get increased HP levels, but this should give you some idea of the concept. From a marketing and sales aspect, this ensures that the public will continually be interested in the new year models, even if the body style does not change. While this FAQ is not about the science and art of auto sales, this may give you an insight as to why the stock ECU is not 100% perfectly tuned from the factory.

 

What are the least talked about benefits of engine management? Engine management solutions to one degree or another can reduce or eliminate black tailpipes, improve driveability throughout the powerband, eliminate the open/closed loop delay in 04+ Subarus, and increase MPG.

 

What Subarus NEED engine management? While every Subaru will benefit from engine management, the 04+ turbo models (except STI) "require" it. The reason for this is the EPA mandated greater restrictions on ECUs for 2004+ and allow manufacturers to exclude one model. Subaru chose the STI as the exclusion, so the restrictions are not on the STI. The restrictions have to do with the open and closed loop fueling. To put the restrictions in a nutshell without being technical, there is a delay between open and closed loop fueling that can allow your 04+ Subaru to run lean during this crossover point in how your car gets fuel. Lean is dangerous as it produces detonation which is the #1 factor is blown pistons. In stock configuration, 04+ turbo models are fine, but modifications such as exhaust work or higher really necessitate the use of engine management as those mods cause the fueling issue to rear it's head. Yes, you can run certain mods for a short time until you get engine management, but you should never kid yourself on 04+ turbo models that bolt on modifications are fine without engine management.

 

What about manual/electronic boost controllers or air fuel controllers?

A manual/electronic boost controller or air fuel controller really isn't engine management. MBCs are fine when used correctly on 02/03 WRX and 04+ STI by a judicious user. The issue gets further clouded on 04+ turbo models less STI, due to the open/closed loop delay. One can lump in the mix air/fuel controllers as well for the same reason. Usually those two devices are used by either cheap skates, n00bs, or advanced users who combine them with other forms of real engine management.

 

What types of engine management solutions are available? They fall into one of these general categories:

a. Reflashed ECU

b. Custom Tuned ECU

c. Piggyback Engine Management

d. Stand Alone Engine Management

e. Open Source Engine Management

 

Reflashed off the shelf ECU: This is your stock ECU that has had the programming modified. This form of engine management is best suited for people who:

a. Have a “set it and forget it” attitude towards engine management

b. Live in remote areas and do not have easy access to a tuner

c. Do not want to learn or are uneasy doing their own tuning

d. Want to modify their vehicle to a certain level and quit or add parts very infrequently

 

It is important to note that while reflashed ECUs are considered a static engine management option, they can be custom tuned by the end user by utilizing additional add-ons from the manufacturer or via a custom tuned reflash by an authorized tuner.

 

In addition, also consider that EcuTek tuners might have reflashes for your exact equipment set-up based on their prior custom tunes. This means that someone who has a full TBE might find the Cobb AccessPort a better plug and play solution, while someone with a full TBE, uppipe, headers, & a lightweight pulley may find an EcuTek reflash a better plug and play solution if they can find an EcuTek tuner with that exact map.

 

Recently for AccessPORT users, "custom maps" have become vogue. These come in the form of more specific maps for specific mods. Let say you have a stage 2 car with headers, TGV deletes, and a pulley. You email this information to a tuner and they will create a custom map for those mods to use. Some will send you a map and logging software, you load the map and data log, then the tuner sends you a final customized tune. While not as perfect as an in-person/on-dyno custom tune, it's a great resource for those in areas without tuners. Companies that do this are PDX Tuning, Perrin, and Clark Turner.

 

Examples of reflashed ECUs are the Cobb AccessPort and EcuTek (including Prodrive’s PPP & Vishnu’s reflash).

 

Reflashed custom tuned ECU: This is the next evolution to a reflashed ECU. This allows either the end user or a professional tuner to custom tune your vehicle to your specific modifications, wants and desires, type of gasoline used, and geographic area. This form of engine management is best suited for people who:

a. Will probably modify their vehicle frequently and require additional tuning

b. People with the ability to do their own tuning

c. People that live close to a tuner

d. People that want to get the maximum power and safety out of their car

 

Examples of Custom Tuned ECUs are Cobb Tuning’s StreetTUNER for end user tuning, Cobb Tuning’s ProTuner for professional custom tunes, EcuTek custom tune via an EcuTek tuner, and EcuTek's DeltaDash Live User Tuning, an end user tuning solution.

 

Piggyback Engine Management: This is an engine management option that works in conjunction with your stock ECU. Depending on the manufacturer, this solution works by the piggyback unit controlling some engine management functions and the stock ECU controlling others. This form of engine management is best suited for people who:

a. Will probably modify their vehicle frequently and require additional tuning

b. People with the ability to do their own tuning

c. People that live close to a tuner

d. People that want to get the maximum power and safety out of their car

 

It is important to mention that most piggyback units come with base maps. These base maps work very similar in function to a reflashed ECU whereas you can run the base map and be 100% fine, or when the day comes for someone to tune their own car or have it professionally tuned, they may do so.

 

Examples of Piggyback Engine Management are Unichip, Xede, UTEC, and others.

 

Stand Alone Engine Management: This is an engine management solution that totally replaces the stock ECU and controls 100% of the engine’s functions. This form of engine management is best suited for people who:

a. Will probably modify their vehicle frequently and require additional tuning

b. People with the ability to do their own tuning

c. People that live close to a tuner

d. People that want to get the maximum power and safety out of their car

 

This form of engine management is generally reserved for more advanced users and people going for really high levels of performance.

 

It is important to mention that most stand alone systems do come with base maps. Unlike the base maps that come on reflashed ECUs, these base maps are meant for your vehicle to run for a short period of time and are not meant to be used as a permanent solution as is the case with the other base maps as described above. Consider these base maps as merely as short term option until end user or a professional tuning.

 

Examples of stand alone engine management are MoTeC, Hydra, AEM, and others.

 

Open Source Engine Management: This can be the cheapest source of engine management available. In essence, you use a laptop, software, and a cable to reflash your stock ECU. Can be used to flash "staged maps" as a set it and forget it option or as a dynamic tuning tool either through tuners or by the end user. This form of engine management is best suited for people who:

 

Group 1:

A. Already have a good degree of tuning knowledge and understand the logic of the factory ECU (or have a strong desire to learn both).

B. Want to constantly tweak and experiment with their own tune. They actually enjoy the process.

C. May be changing/upgrading mods frequently.

 

Group 2:

A. Looking to get a custom tune from a professional but cannot afford or do not want to spend the money on license fees and/or hardware costs required of Cobb, Ecutek, etc. That is, they want their car to have a custom tune from a pro at the least cost. More and more professional shops are offering open source tunes and they can be just as capable as tunes from the commercial software.

B. Want an inexpensive (ex. XPT) or free (created by another user) OTS map. Might not go with EM otherwise because they feel it is too expensive. They are willing to learn the basics of logging with RomRaider to make sure the tune doesn't have any issues with their car.

 

Those people where Open Source Engine Management would be a BAD choice (assuming they are doing it themselves and not a professional tuner):

1. Want the easiest to use, troubleshoot, and closest thing to "set and forget" EM solution.

2. Are computer illiterate.

 

Examples of Open Source Engine Management are RomRaider, formerly known as Enginuity, EcuFlash, and others.

 

Can the dealer detect my reflashed ECU (AccessPort/EcuTek/Open Source)?

 

YES the checksum of the ECU changes.

YES the dealer can easily read the checksum.

 

NO the dealer has nothing to compare the checksum against there are many revisions of the WRX ecu they all have different checksums. If the dealer had someway of putting this checksum into a database he COULD verify that the code had been modified but at this time he doesn't.

 

The 05+ ECU and some of the 04s have the VIN in the ECU code. The current versions of reflashed ECUs only change the tables so the VIN will report when queried.

 

Bottom line: If you don't want modifications to be detected, don't modify the car.

 

What are some specific types of engine management While this FAQ does not go into specifics for every type of engine management, this thread covers many types. This link offers several comparisons of different system features as well. There are some not covered in these threads though and may be considered as well.

 

Generally speaking, what engine management option will give me the most power? Custom tuned engine management solutions will always give you more power. Every off the shelf engine management solution has a built in safety factor. This depends on the manufacturer. This is because their “Stage 1” or “VF-30” map has to safely make power for someone living in Phoenix’s heat and 91 octane, to Denver’s high altitude, to Boston’s cold and 93 octane. The gasoline and geographic variances can leave horsepower on the table.

 

More specifically, what engine management option will give me the most power? This is one question without a correct answer. Let’s say that you research a very comprehensive stand alone engine management system such as a MoTeC unit and decide that it’s the “best” for your car. At the end of the day, it’s about what the tuner is most comfortable with. Some tuners may be able to extract better results from a “lesser” system simply because they understand the interface better.

 

For someone interested in tuning their own vehicle, they should match their tuning skills with an engine management solution that they are able to understand and use correctly. For someone interested in professional tuning, they should consult with their tuner for their recommendations. Both of these actions will ensure a good tune with a minimum amount of rework, guessing, and trial and error. While most tuners are capable of learning new or more advanced engine management systems, consider the benefits of an “older/worse system” your tuner is familiar with vs. your tuner learning a “newer/better system” at $200/hour plus possible dyno time.

 

I have a reflashed ECU and am not seeing their advertised HP, why? First off, have you met their criteria EXACTLY? The #1 cause of low HP with reflashed ECU owners is their lack of meeting the manufacturer’s requirements. If they require a full turbo back exhaust and you only have a downpipe and a cat back exhaust, 100% of the blame is on the end user. As well, if they require a full exhaust and you have a full exhaust, uppipe, headers, and a bigger top mount intercooler, this can cause problems as well.

 

Also realize that HP figures vary. You cannot compare (for example) a manufacturer’s Mustang Dyno HP figures to your local DynoJet HP figures. Even comparing identical dynos to each other is futile as dyno software set-up, altitude, temperature, humidity, and other factors do not ensure an equal result.

 

In addition, realize that a reflashed ECU still utilizes many of the stock ECU’s learning functions. This means that in a perfect world, you will see the advertised HP from your reflashed ECU. This may also mean that on the day of dyno testing, your octane, the temperature, humidity, and many other factors are considered by the reflashed ECU when determining total power output. If the advertised numbers aren't there on dyno day, it doesn’t necessarily mean there is a problem, but rather, your ECU is protecting your engine from low octane, high temperature, high humidity, or other factors.

 

How much is a custom tune by a professional? Expect to pay $100-$150 per hour for the dyno time. Your tuner’s fee depends on their level of experience and pricing. Tuners generally charge $100-200 per hour for their time. The amount of total tuning time depends on the tuner and the amount of time you wish for them to tune your vehicle. Most tuners can get your vehicle within 90-95% of its maximum power within 1-2 hours.

 

[broknindarkagain]

I cam across an interesting article. It explains so of the reasons WHY you need Engine Management when you start modifying a car.

LINK

 

Engine Basics: Detonation and Pre-Ignition

 

by Allen W. Cline

 

 

Introduction

All high output engines are prone to destructive tendencies as a result of over boost, misfueling, mis-tuning and inadequate cooling. The engine community pushes ever nearer to the limits of power output. As they often learn cylinder chamber combustion processes can quickly gravitate to engine failure. This article defines two types of engine failures, detonation and pre-ignition, that are as insidious in nature to users as they are hard to recognize and detect. This discussion is intended only as a primer about these combustion processes since whole books have been devoted to the subject.

 

First, let us review normal combustion. It is the burning of a fuel and air mixture charge in the combustion chamber. It should burn in a steady, even fashion across the chamber, originating at the spark plug and progressing across the chamber in a three dimensional fashion. Similar to a pebble in a glass smooth pond with the ripples spreading out, the flame front should progress in an orderly fashion. The burn moves all the way across the chamber and, quenches (cools) against the walls and the piston crown. The burn should be complete with no remaining fuel-air mixture. Note that the mixture does not "explode" but burns in an orderly fashion.

 

There is another factor that engineers look for to quantify combustion. It is called "location of peak pressure (LPP)." It is measured by an in-cylinder pressure transducer. Ideally, the LPP should occur at 14 degrees after top dead center. Depending on the chamber design and the burn rate, if one would initiate the spark at its optimum timing (20 degrees BTDC, for example) the burn would progress through the chamber and reach LPP, or peak pressure at 14 degrees after top dead center. LPP is a mechanical factor just as an engine is a mechanical device. The piston can only go up and down so fast. If you peak the pressure too soon or too late in the cycle, you won't have optimum work. Therefore, LPP is always 14 degrees ATDC for any engine.

I introduce LPP now to illustrate the idea that there is a characteristic pressure buildup (compression and combustion) and decay (piston downward movement and exhaust valve opening) during the combustion process that can be considered "normal" if it is smooth, controlled and its peak occurs at 14 degrees ATDC.

 

Our enlarged definition of normal combustion now says that the charge/bum is initiated with the spark plug, a nice even burn moves across the chamber, combustion is completed and peak pressure occurs at at 14 ATDC.

 

Confusion and a lot of questions exist as to detonation and pre-ignition. Sometimes you hear mistaken terms like "pre-detonation". Detonation is one phenomenon that is abnormal combustion. Pre-ignition is another phenomenon that is abnormal combustion. The two, as we will talk about, are somewhat related but are two distinctly different phenomenon and can induce distinctly different failure modes.

 

Key Definitions

Detonation

Detonation is the spontaneous combustion of the end-gas (remaining fuel/air mixture) in the chamber. It always occurs after normal combustion is initiated by the spark plug. The initial combustion at the spark plug is followed by a normal combustion burn. For some reason, likely heat and pressure, the end gas in the chamber spontaneously combusts. The key point here is that detonation occurs after you have initiated the normal combustion with the spark plug.

Pre-ignition

Pre-ignition is defined as the ignition of the mixture prior to the spark plug firing. Anytime something causes the mixture in the chamber to ignite prior to the spark plug event it is classified as pre-ignition. The two are completely different and abnormal phenomenon.

 

Detonation

Unburned end gas, under increasing pressure and heat (from the normal progressive burning process and hot combustion chamber metals) spontaneously combusts, ignited solely by the intense heat and pressure. The remaining fuel in the end gas simply lacks sufficient octane rating to withstand this combination of heat and pressure.

 

Detonation causes a very high, very sharp pressure spike in the combustion chamber but it is of a very short duration. If you look at a pressure trace of the combustion chamber process, you would see the normal burn as a normal pressure rise, then all of a sudden you would see a very sharp spike when the detonation occurred. That spike always occurs after the spark plug fires. The sharp spike in pressure creates a force in the combustion chamber. It causes the structure of the engine to ring, or resonate, much as if it were hit by a hammer. Resonance, which is characteristic of combustion detonation, occurs at about 6400 Hertz. So the pinging you hear is actually the structure of the engine reacting to the pressure spikes. This noise of detonation is commonly called spark knock. This noise changes only slightly between iron and aluminum. This noise or vibration is what a knock sensor picks up. The knock sensors are tuned to 6400 hertz and they will pick up that spark knock. Incidentally, the knocking or pinging sound is not the result of "two flame fronts meeting" as is often stated. Although this clash does generate a spike the noise you sense comes from the vibration of the engine structure reacting to the pressure spike.

 

One thing to understand is that detonation is not necessarily destructive. Many engines run under light levels of detonation, even moderate levels. Some engines can sustain very long periods of heavy detonation without incurring any damage. If you've driven a car that has a lot of spark advance on the freeway, you'll hear it pinging. It can run that way for thousands and thousands of miles. Detonation is not necessarily destructive. It's not an optimum situation but it is not a guaranteed instant failure. The higher the specific output (HP/in3) of the engine, the greater the sensitivity to detonation. An engine that is making 0.5 HP/in3 or less can sustain moderate levels of detonation without any damage; but an engine that is making 1.5 HP/in3, if it detonates, it will probably be damaged fairly quickly, here I mean within minutes.

 

Detonation causes three types of failure:

1. Mechanical damage (broken ring lands)

2. Abrasion (pitting of the piston crown)

3. Overheating (scuffed piston skirts due to excess heat input or high coolant temperatures)

 

The high impact nature of the spike can cause fractures; it can break the spark plug electrodes, the porcelain around the plug, cause a clean fracture of the ring land and can actually cause fracture of valves-intake or exhaust. The piston ring land, either top or second depending on the piston design, is susceptible to fracture type failures. If I were to look at a piston with a second broken ring land, my immediate suspicion would be detonation.

 

Another thing detonation can cause is a sandblasted appearance to the top of the piston. The piston near the perimeter will typically have that kind of look if detonation occurs. It is a swiss-cheesy look on a microscopic basis. The detonation, the mechanical pounding, actually mechanically erodes or fatigues material out of the piston. You can typically expect to see that sanded look in the part of the chamber most distant from the spark plug, because if you think about it, you would ignite the flame front at the plug, it would travel across the chamber before it got to the farthest reaches of the chamber where the end gas spontaneously combusted. That's where you will see the effects of the detonation; you might see it at the hottest part of the chamber in some engines, possibly by the exhaust valves. In that case the end gas was heated to detonation by the residual heat in the valve.

 

 

In a four valve engine with a pent roof chamber with a spark plug in the center, the chamber is fairly uniform in distance around the spark plug. But one may still may see detonation by the exhaust valves because that area is usually the hottest part of the chamber. Where the end gas is going to be hottest is where the damage, if any, will occur.

 

Because this pressure spike is very severe and of very short duration, it can actually shock the boundary layer of gas that surrounds the piston. Combustion temperatures exceed 1800 degrees. If you subjected an aluminum piston to that temperature, it would just melt. The reason it doesn't melt is because of thermal inertia and because there is a boundary layer of a few molecules thick next to the piston top. This thin layer isolates the flame and causes it to be quenched as the flame approaches this relatively cold material. That combination of actions normally protects the piston and chamber from absorbing that much heat. However, under extreme conditions the shock wave from the detonation spike can cause that boundary layer to breakdown which then lets a lot of heat transfer into those surfaces.

 

Engines that are detonating will tend to overheat, because the boundary layer of gas gets interrupted against the cylinder head and heat gets transferred from the combustion chamber into the cylinder head and into the coolant. So it starts to overheat. The more it overheats, the hotter the engine, the hotter the end gas, the more it wants to detonate, the more it wants to overheat. It's a snowball effect. That's why an overheating engine wants to detonate and that's why engine detonation tends to cause overheating.

 

Many times you will see a piston that is scuffed at the "four corners". If you look at the bottom side of a piston you see the piston pin boss. If you look across each pin boss, it's solid aluminum with no flexibility. It expands directly into the cylinder wall. However, the skirt of a piston is relatively flexible. If it gets hot, it can deflect. The crown of the piston is actually slightly smaller in diameter on purpose so it doesn't contact the cylinder walls. So if the piston soaks up a lot of heat, because of detonation for instance, the piston expands and drives the piston structure into the cylinder wall causing it to scuff in four places directly across each boss. It's another dead give-a-way sign of detonation. Many times detonation damage is just limited to this.

 

Some engines, such as liquid cooled 2-stroke engines found in snowmobiles, watercraft and motorcycles, have a very common detonation failure mode. What typically happens is that when detonation occurs the piston expands excessively, scuffs in the bore along those four spots and wipes material into the ring grooves. The rings seize so that they can't conform to the cylinder walls. Engine compression is lost and the engine either stops running, or you start getting blow-by past the rings. That torches out an area. Then the engine quits.

 

In the shop someone looks at the melted result and says, "pre-ignition damage". No, it's detonation damage. Detonation caused the piston to scuff and this snowballed into loss of compression and hot gas escaping by the rings that caused the melting. Once again, detonation is a source of confusion and it is very difficult, sometimes, to pin down what happened, but in terms of damage caused by detonation, this is another typical sign.

 

While some of these examples may seem rather tedious I mention them because a "scuffed piston" is often blamed on other factors and detonation as the problem is overlooked. A scuffed piston may be an indicator of a much more serious problem which may manifest itself the next time with more serious results.

 

In the same vein, an engine running at full throttle may be happy due to a rich WOT air/fuel ratio. Throttling back to part throttle the mixture may be leaner and detonation may now occur. Bingo, the piston overheats and scuffs, the engine fails but the postmortem doesn't consider detonation because the failure didn't happen at WOT.

 

I want to reinforce the fact that the detonation pressure spike is very brief and that it occurs after the spark plug normally fires. In most cases that will be well after ATDC, when the piston is moving down. You have high pressure in the chamber anyway with the burn. The pressure is pushing the piston like it's supposed to, and superimposed on that you get a brief spike that rings the engine.

 

Causes

Detonation is influenced by chamber design (shape, size, geometry, plug location), compression ratio, engine timing, mixture temperature, cylinder pressure and fuel octane rating. Too much spark advance ignites the burn too soon so that it increases the pressure too greatly and the end gas spontaneously combusts. Backing off the spark timing will stop the detonation. The octane rating of the fuel is really nothing magic. Octane is the ability to resist detonation. It is determined empirically in a special running test engine where you run the fuel, determine the compression ratio that it detonates at and compare that to a standard fuel, That's the octane rating of the fuel. A fuel can have a variety of additives or have higher octane quality. For instance, alcohol as fuel has a much better octane rating just because it cools the mixture significantly due to the extra amount of liquid being used. If the fuel you got was of a lower octane rating than that demanded by the engine's compression ratio and spark advance detonation could result and cause the types of failures previously discussed.

 

Production engines are optimized for the type or grade of fuel that the marketplace desires or offers. Engine designers use the term called MBT (Minimum spark for Best Torque) for efficiency and maximum power; it is desirable to operate at MBT at all times. For example, let's pick a specific engine operating point, 4000 RPM, WOT, 98 kPa MAP. At that operating point with the engine on the dynamometer and using non-knocking fuel, we adjust the spark advance. There is going to be a point where the power is the greatest. Less spark than that, the power falls off, more spark advance than that, you don't get any additional power.

 

Now our engine was initially designed for premium fuel and was calibrated for 20 degrees of spark advance. Suppose we put regular fuel in the engine and it spark knocks at 20 degrees? We back off the timing down to 10 degrees to get the detonation to stop. It doesn't detonate any more, but with 10 degrees of spark retard, the engine is not optimized anymore. The engine now suffers about a 5-6 percent loss in torque output. That's an unacceptable situation. To optimize for regular fuel engine designers will lower the compression ratio to allow an increase in the spark advance to MBT. The result, typically, is only a 1-2 percent torque loss by lowering the compression. This is a better trade-off. Engine test data determines how much compression an engine can have and run at the optimum spark advance.

 

For emphasis, the design compression ratio is adjusted to maximize efficiency/power on the available fuel. Many times in the aftermarket the opposite occurs. A compression ratio is "picked" and the end user tries to find good enough fuel and/or retards the spark to live with the situation...or suffers engine damage due to detonation.

 

Another thing you can do is increase the burn rate of the combustion chamber. That is why with modem engines you hear about fast burn chambers or quick burn chambers. The goal is the faster you can make the chamber burn, the more tolerant to detonation it is. It is a very simple phenomenon, the faster it burns, the quicker the burn is completed, the less time the end gas has to detonate. If it can't sit there and soak up heat and have the pressure act upon it, it can't detonate.

 

If, however, you have a chamber design that burns very slowly, like a mid-60s engine, you need to advance the spark and fire at 38 degrees BTDC. Because the optimum 14 degrees after top dead center (LPP) hasn't changed the chamber has far more opportunity to detonate as it is being acted upon by heat and pressure. If we have a fast burn chamber, with 15 degrees of spark advance, we've reduced our window for detonation to occur considerably. It's a mechanical phenomenon. That's one of the goals of having a fast burn chamber because it is resistant to detonation.

 

There are other advantages too, because the faster the chamber burns, the less spark advance you need. The less time pistons have to act against the pressure build up, the air pump becomes more efficient. Pumping losses are minimized. In other words, as the piston moves towards top dead center compression of the fuel/air mixture increases. If you light the fire at 38 degrees before top dead center, the piston acts against that pressure for 38 degrees. If you light the spark 20 degrees before top dead center, it's only acting against it for 20. The engine becomes more mechanically efficient.

 

There are a lot of reasons for fast burn chambers but one nice thing about them is that they become more resistant to detonation. A real world example is the Northstar engine from 1999 to 2000. The 1999 engine was a 10.3:1 compression ratio. It was a premium fuel engine. For the 2000 model year, we revised the combustion chamber, achieved faster burn. We designed it to operate on regular fuel and we only had to lower the compression ratio .3 to only 10:1 to make it work. Normally, on a given engine (if you didn't change the combustion chamber design) to go from premium to regular fuel, it will typically drop one point in compression ratio: With our example, you would expect a Northstar engine at 10.3:1 compression ratio, dropped down to 9.3:1 in order to work on regular. Because of the faster burn chamber, we only had to drop to 10:1. The 10:1 compression ratio still has very high compression with attendant high mechanical efficiency and yet we can operate it at optimum spark advance on regular fuel. That is one example of spark advance in terms of technology. A lot of that was achieved through computational fluid dynamics analysis of the combustion chamber to improve the swirl and tumble and the mixture motion in the chamber to enhance the burn rate.

 

Camber Design

One of the characteristic chambers that people are familiar with is the Chrysler Hemi. The engine had a chamber that was like a half of a baseball. Hemispherical in nature and in nomenclature, too. The two valves were on either side of the chamber with the spark plug at the very top. The charge burned downward across the chamber. That approach worked fairly well in passenger car engines but racing versions of the Hemi had problems. Because the chamber was so big and the bores were so large, the chamber volume also was large; it was difficult to get the compression ratio high. Racers put a dome on the piston to increase the compression ratio. If you were to take that solution to the extreme and had a 13:1 or 14:1 compression ratio in the engine pistons had a very tall dome. The piston dome almost mimicked the shape of the head's combustion chamber with the piston at top dead center. One could call the remaining volume "the skin of the orange." When ignited the charge burned very slowly, like the ripples in a pond,, covering the distance to the block cylinder wall. Thus, those engines, as a result of the chamber design, required a tremendous amount of spark advance, about 40-45 degrees. With that much spark advance detonation was a serious possibility if not fed high octane fuel. Hemis tended to be very sensitive to tuning. As often happened, one would keep advancing the spark, get more power and all of a sudden the engine would detonate, Because they were high output engines, turning at high RPM, things would happen suddenly.

 

Hemi racing engines would typically knock the ring land off, get blow by, torch the piston and fall apart. No one then understood why. We now know that the Hemi design is at the worst end of the spectrum for a combustion chamber. A nice compact chamber is best; that's why the four valve pent roof style chambers are so popular. The flatter the chamber, the smaller the closed volume of the chamber, the less dome you need in the piston. We can get inherently high compression ratios with a flat top piston with a very nice bum pattern right in the combustion chamber, with very short distances, with very good mixture motion - a very efficient chamber.

 

Look at a Northstar or most of the 4 valve type engines - all with flat top pistons, very compact combustion chambers, very narrow valve angles and there is no need for a dome that impedes the burn to raise the compression ratio to 10:1.

 

 

Detonation Indicators

The best indication of detonation is the pinging sound that cars, particularly old models, make at low speeds and under load. It is very difficult to hear the sound in well insulated luxury interiors of today's cars. An unmuffled engine running straight pipes or a propeller turning can easily mask the characteristic ping. The point is that you honestly don't know that detonation is going on. In some cases, the engine may smoke but not as a rule. Broken piston ring lands are the most typical result of detonation but are usually not spotted. If the engine has detonated visual signs like broken spark plug porcelains or broken ground electrodes are dead giveaways and call for further examination or engine disassembly.

 

It is also very difficult to sense detonation while an engine is running in a remote and insulated dyno test cell. One technique seems almost elementary but, believe it or not, it is employed in some of the highest priced dyno cells in the world. We refer to it as the "Tin Ear". You might think of it as a simple stethoscope applied to the engine block. We run a ordinary rubber hose from the dyno operator area next to the engine. To amplify the engine sounds we just stick the end of the hose through the bottom of a Styrofoam cup and listen in! It is common for ride test engineers to use this method on development cars particularly if there is a suspicion out on the road borderline detonation is occurring. Try it on your engine; you will be amazed at how well you can hear the different engine noises.

 

The other technique is a little more subtle but usable if attention is paid to EGT (Exhaust Gas Temperature). Detonation will actually cause EGTs to drop. This behavior has fooled a lot of people because they will watch the EGT and think that it is in a low enough range to be safe, the only reason it is low is because the engine is detonating.

 

The only way you know what is actually happening is to be very familiar with your specific engine EGT readings as calibrations and probe locations vary. If, for example, you normally run 1500 degrees at a given MAP setting and you suddenly see 1125 after picking up a fresh load of fuel you should be alert to possible or incipient detonation. Any drop from normal EGT should be reason for concern. Using the "Tin Ear" during the early test stage and watching the EGT very carefully, other than just plain listening with your ear without any augmentation, is the only way to identify detonation. The good thing is, most engines will live with a fairly high level of detonation for some period of time. It is not an instantaneous type failure.

 

The definition of pre-ignition is the ignition of the fuel/air charge prior to the spark plug firing. Pre-ignition caused by some other ignition source such as an overheated spark plug tip, carbon deposits in the combustion chamber and, rarely, a burned exhaust valve; all act as a glow plug to ignite the charge.

 

Keep in mind the following sequence when analyzing pre-ignition. The charge enters the combustion chamber as the piston reaches BDC for intake; the piston next reverses direction and starts to compress the charge. Since the spark voltage requirements to light the charge increase in proportion with the amount of charge compression; almost anything can ignite the proper fuel/air mixture at BDC!! BDC or before is the easiest time to light that mixture. It becomes progressively more difficult as the pressure starts to build.

 

The definition of pre-ignition is the ignition of the fuel/air charge prior to the spark plug firing. Pre-ignition caused by some other ignition source such as an overheated spark plug tip, carbon deposits in the combustion chamber and, rarely, a burned exhaust valve; all act as a glow plug to ignite the charge.

continued on next post

[broknindarkagain]

Keep in mind the following sequence when analyzing pre-ignition. The charge enters the combustion chamber as the piston reaches BDC for intake; the piston next reverses direction and starts to compress the charge. Since the spark voltage requirements to light the charge increase in proportion with the amount of charge compression; almost anything can ignite the proper fuel/air mixture at BDC!! BDC or before is the easiest time to light that mixture. It becomes progressively more difficult as the pressure starts to build.

 

A glowing spot somewhere in the chamber is the most likely point for pre-ignition to occur. It is very conceivable that if you have something glowing, like a spark plug tip or a carbon ember, it could ignite the charge while the piston is very early in the compression stoke. The result is understandable; for the entire compression stroke, or a great portion of it, the engine is trying to compress a hot mass of expanded gas. That obviously puts tremendous load on the engine and adds tremendous heat into its parts. Substantial damage occurs very quickly. You can't hear it because there is no rapid pressure rise. This all occurs well before the spark plug fires.

 

Remember, the spark plug ignites the mixture and a sharp pressure spike occurs after that, when the detonation occurs. That's what you hear. With pre-ignition, the ignition of the charge happens far ahead of the spark plug firing, in my example, very, very far ahead of it when the compression stroke just starts. There is no very rapid pressure spike like with detonation. Instead, it is a tremendous amount of pressure which is present for a very long dwell time, i.e., the entire compression stroke. That's what puts such large loads on the parts. There is no sharp pressure spike to resonate the block and the head to cause any noise. So you never hear it, the engine just blows up! That's why pre-ignition is so insidious. It is hardly detectable before it occurs. When it occurs you only know about it after the fact. It causes a catastrophic failure very quickly because the heat and pressures are so intense.

 

An engine can live with detonation occurring for considerable periods of time, relatively speaking. There are no engines that will live for any period of time when pre-ignition occurs. When people see broken ring lands they mistakenly blame it on pre-ignition and overlook the hammering from detonation that caused the problem. A hole in the middle of the piston, particularly a melted hole in the middle of a piston, is due to the extreme heat and pressure of pre-ignition.

 

Other signs of pre-ignition are melted spark plugs showing splattered, melted, fused looking porcelain. Many times a "pre-ignited plug" will melt away the ground electrode. What's left will look all spattered and fuzzy looking. The center electrode will be melted and gone and its porcelain will be spattered and melted. This is a typical sign of incipient pre-ignition.

 

The plug may be getting hot, melting and "getting ready" to act as a pre-ignition source. The plug can actually melt without pre-ignition occurring. However, the melted plug can cause pre-ignition the next time around.

 

The typical pre-ignition indicator, of course, would be the hole in the piston. This occurs because in trying to compress the already burned mixture the parts soak up a tremendous amount of heat very quickly. The only ones that survive are the ones that have a high thermal inertia, like the cylinder head or cylinder wall. The piston, being aluminum, has a low thermal inertia (aluminum soaks up the heat very rapidly). The crown of the piston is relatively thin, it gets very hot, it can't reject the heat, it has tremendous pressure loads against it and the result is a hole in the middle of the piston where it is weakest.

 

I want to emphasis that when most people think of pre-ignition, they generally accept the fact that the charge was ignited before the spark plug fires. However, I believe they limit their thinking to 5-10 degrees before the spark plug fires. You have to really accept that the most likely point for pre-ignition to occur is 180 degrees BTDC, some 160 degrees before the spark plug would have fired because that's the point (if there is a glowing ember in the chamber) when it's most likely to be ignited. We are talking some 160-180 degrees of bum being compressed that would normally be relatively cool. A piston will only take a few revolutions of that distress before it fails. As for detonation, it can get hammered on for seconds, minutes, or hours depending on the output of the engine and the load, before any damage occurs. Pre-ignition damage is almost instantaneous.

 

When the piston crown temperature rises rapidly it never has time to get to the skirt and expand and cause it to scuff. It just melts the center right out of the piston. That's the biggest difference between detonation and pre-ignition when looking at piston failures. Without a high pressure spike to resonate the chamber and block, you would never hear pre-ignition. The only sign of pre-ignition is white smoke pouring out the tailpipe and the engine quits running.

 

The engine will not run more than a few seconds with pre-ignition. The only way to control pre-ignition is just keep any pre-ignition sources at bay. Spark plugs should be carefully matched to the recommended heat range. Racers use cold spark plugs and relatively rich mixtures. Spark plug heat range is also affected by coolant temperatures. A marginal heat range plug can induce pre-ignition because of an overheated head (high coolant temperature or inadequate flow). Also, a loose plug can't reject sufficient heat through its seat. A marginal heat range plug running lean (suddenly?) can cause pre-ignition.

 

Passenger car engine designers face a dilemma. Spark plugs must cold start at -40 degrees F. (which calls for hot plugs that resist fouling) yet be capable of extended WOT operation (which calls for cold plugs and maximum heat transfer to the cylinder head).

 

Here is how spark plug effectiveness or "pre-ignition" testing is done at WOT. Plug tip/gap temperature is measured with a blocking diode and a small battery supplying current through a milliamp meter to the spark plug terminal. The secondary voltage cannot come backwards up the wire because the large blocking diode prevents it.

 

As the spark plug tip heats up, it tends to ionize the gap and small levels of current will flow from the battery as indicated by the milliamp gauge. The engine is run under load and the gauges are closely watched. Through experience techni-cians learn what to expect from the gauges. Typically, very light activity, just a few milliamps of current, is observed across the spark plug gap. In instances where the spark plug tip/gap gets hot enough to act as an ignition source the milliamp current flow suddenly jumps off scale. When that happens, instant power reduction is necessary to avoid major engine damage.

 

Back in the 80s, running engines that made half a horsepower per cubic inch, we could artificially and safely induce pre-ignition by using too hot of a plug and leaning out the mixture. We could determine how close we were by watching the gauges and had plenty of time (seconds) to power down, before any damage occurred.

 

With the Northstar making over 1 HP per cubic inch, at 6000 RPM, if the needles move from nominal, you just failed the engine. It's that quick! When you disassemble the engine, you'll find definite evidence of damage. It might be just melted spark plugs. But pre-ignition happens that quick in high output engines. There is very little time to react.

 

If cold starts and plug fouling are not a major worry run very cold spark plugs. A typical case of very cold plug application is a NASCAR type engine. Because the prime pre-ignition source is eliminated engine tuners can lean out the mixture (some) for maximum fuel economy and add a lot of spark advance for power and even risk some levels of detonation. Those plugs are terrible for cold starting and emissions and they would foul up while you were idling around town but for running at full throttle at 8000 RPM, they function fine. They eliminate a variable that could induce pre-ignition.

 

Engine developers run very cold spark plugs to avoid the risk of getting into pre-ignition during engine mapping of air/fuel and spark advance, Production engine calibration requires that we have much hotter spark plugs for cold startability and fouling resistance. To avoid pre-ignition we then compensate by making sure the fuel/air calibration is rich enough to keep the spark plugs cool at high loads and at high temperatures, so that they don't induce pre-ignition.

 

Consider the Northstar engine. If you do a full throttle 0-60 blast, the engine will likely run up to 6000 RPM at a 11.5:1 or 12:1 air fuel ratio. But under sustained load, at about 20 seconds, that air fuel ratio is richened up by the PCM to about 10:1. That is done to keep the spark plugs cool, as well as the piston crowns cool. That richness is necessary if you are running under continuous WOT load. A slight penalty in horsepower and fuel economy is the result. To get the maximum acceleration out of the engine, you can actually lean it out, but under full load, it has to go back to rich. Higher specific output engines are much more sensitive to pre-ignition damage because they are turning more RPM, they are generating a lot more heat and they are burning more fuel. Plugs have a tendency to get hot at that high specific output and reaction time to damage is minimal.

 

A carburetor set up for a drag racer would never work on a NASCAR or stock car engine because it would overheat and cause pre-ignition. But on the drag strip for 8 or 10 seconds, pre-ignition never has time to occur, so dragsters can get away with it. Differences in tuning for those two different types of engine applications are dramatic. That's why a drag race engine would make a poor choice for an aircraft engine.

 

Muddy Water

There is a situation called detonation induced pre-ignition. I don't want to sound like double speak here but it does happen. Imagine an engine under heavy load starting to detonate. Detonation continues for a long period of time. The plug heats up because the pressure spikes break down the protective boundary layer of gas surrounding the electrodes. The plug temperature suddenly starts to elevate unnaturally, to the point when it becomes a glow plug and induces pre-ignition. When the engine fails, I categorize that result as "detonation induced pre-ignition." There would not have been any danger of pre-ignition if the detonation had not occurred. Damage attributed to both detonation and pre-ignition would be evident.

 

Typically, that is what we see in passenger car engines. The engines will typically live for long periods of time under detonation. In fact, we actually run a lot of piston tests where we run the engine at the torque peak, induce moderate levels of detonation deliberately. Based on our resulting production design, the piston should pass those tests without any problem; the pistons should be robust enough to survive. If, however, under circumstances due to overheating or poor fuel, the spark plug tip overheats and induces pre-ignition, it's obviously not going to survive. If we see a failure, it probably is a detonation induced pre-ignition situation.

 

I would urge any experimenter to be cautious using automotive based engines in other applications. In general, engines producing .5 HP/in3 (typical air-cooled aircraft engines) can be forgiving (as leaning to peak EGT, etc.). But at 1.0 HP/in3 (very typical of many high performance automotive conversions) the window for calibration induced engine damage is much less forgiving. Start out rich, retarded and with cold plugs and watch the EGTs!

 

Hopefully this discussion will serve as a thought starter. I welcome any communication on this subject. Every application is unique so beware of blanket statements as many variables affect these processes. AWC

[amorgan93]

ill give you credit for this one it needs to be a sticky.. i think ive asked about 3/4 of those questions

[Zues Marine]

use the 'report post' option to contact a mod about stickying..

[broknindarkagain]

didn't think about the "report post" button. I PMed an admin. Thanks for the tip

[Baddog]

I wish I could swap 5 turbos onto my EJ2235

[broknindarkagain]

I wish I could swap 5 turbos onto my EJ2235

 

Wow I've never heard of that engine. How many Subarus did you use to build that one???

[Baddog]

Wow I've never heard of that engine. How many Subarus did you use to build that one???

 

Something like 4? I bought like 3-4 broken Subarus and wanted to Superglue the engine together. But come to find out.....It doesn't work?

 

[broknindarkagain]

Something like 4? I bought like 3-4 broken Subarus and wanted to Superglue the engine together. But come to find out.....It doesn't work?

 

You should have just used an electric super charger on your stock engine n00b.

 

duct tape works better

[subikid90]

Something like 4? I bought like 3-4 broken Subarus and wanted to Superglue the engine together. But come to find out.....It doesn't work?

 

 

I heard mighty putty +10000000 times better than super glue. Billy Mays promises an extra 500whp

[Baddog]

I heard mighty putty +10000000 times better than super glue. Billy Mays promises an extra 500whp

 

[BAC5.2]

So if my transmission isn't strong enough, what should I do?

The easiest thing to do is to find a wrecked donor car. Or you can find a transmission / rear diff combo online. I'm currently running a JDM STI v3 5 speed with a stage 1 clutch. Its good up until about 400awhp.

 

This isn't really true.

 

For the most part, all pre-1999 manual transmissions are the same. The higher the final drive, the more resiliant it will be (strain will be transferred to the more robust ring and pinion, and away from the gears themselves). The slight differences in tooth width are marginal at best, and vary from year to year. If you find a JDM transmission with a 4.44 final drive, that's a pretty good bet for durability but don't expect much from the car in terms of speed. A high final drive like that means a LOT of shifting, and a low top speed.

 

Your best bet, for a given swap, is to source the drivetrain from a 2005-2009 LegacyGT. If you really intend to make some power, source the drivetrain from an 05-09 Outback XT and run the smaller tires suitable to your model year (something in the 225/45/17 or 225/50/16 range). The Outback has a higher final drive, and coupled with the smaller than Outback sized tires, will be a pretty durable drivetrain. You'll be giving up a lot in terms of MPH, but it won't break easily and that matters more if budget is a concern.

 

I would keep power below 300whp if you plan on doing any kind of aggressive driving. That's all that stock 5-speed drivetrains can safely and reliably handle. You'll find lots of people making more than that, but the risks of failure above 300whp increase exponentially.

 

What about my exhaust? I've installed a turbo engine and I can't make the exhaust fit around the subframe. It looks like I have to cut part of it out!

Our stock subframes were not designed to accomadate for the turbo exhaust. The work around for this is to either use an 04 STI or any 02-07 WRX subframe. DO NOT cut your stock subframe. It will not be as strong as it needs to be if you do this.

 

You can use a first generation Legacy Turbo subframe, and that will bolt right in. If you use the WRX subframe, you'll need WRX axles and control arms, or you'll need to put big washers on either side of your stock control arms to make up the gap. The WRX has wider bushings in the control arms.

 

The best budget way to do the swap is to use a Legacy Turbo crossmember. Everything bolts into place then, and you can use takeoff parts from a WRX. Headers, turbo, downpipe and catbacks can be had for dirt cheap secondhand, and they'll all fit.

 

So can you just give me a quick list of the parts I need to do a turbo swap?

This depends on what route you go. If you do a WRX / STI swap, you will need the following

 

• Engine
  
  
• Transmission
  
  
• ECU
  
  
• Wiring
  
  
• Rear Diff
  
  
• Turbo
  
  
• Exhaust
  
  
• Subframe
  
  
• Custom Driveshaft
  
  

 

If you do some kind of JDM swap, you will need all the same stuff listed, except you will not be able to run a stock ECU. With a JDM swap, your best bet is a stand alone ecu system like AEM or Megasquirt. Piggyback systems are an option, but are more trouble then its worth.

 

You don't need half of that stuff.

 

If you really just want to turbo the car, you need the subframe, headers, uppipe, turbo, turboback exhaust, and some kind of aftermarket tuning device. There are literally dozens of options for this aspect of the build, and engine management is the ultimate hiccup in the swap. The mechanical stuff is like playing with legos. The electrical work is a bit more involved and not for the feint of heart.

 

If you want to do a full swap, your best bet is to find a rolled WRX or STi and swap EVERYTHING. This is more difficult if you have a multilink rear suspension, but not terribly so. The heartache and headache saved by having a donor vehicle is immense. If you have a pre-multilink Legacy, you can find almost any year WRX or STi and swap just about everything over. The hardest part becomes wiring the chassis harness up.

 

I chose to do a WRX / STI swap, but I want a little more power out of the stock WRX / STI drivetrain. What can I do?

Before you start upgrading the stock WRX / STI setup, you should look into some kind of piggyback system like a CobbAP. This way, you're able to tune your car to whatever mods you have installed and get all the power out of it. After a piggyback, you can do a rotated turbo setup with something bigger then the TD04 or VF39. Bigger injectors, exhaust, MSD, boost controller, etc are all good upgrades.

 

If you want more power, just browse the powertrain forums. Engine management is necessary, and then just pick and choose your upgrades. Rotated turbos are unnecessary, as are boost controllers. It is outrageously easy to make 300whp out of a stock 2.5L turbo motor. It's all bolt on, and fairly well reliable. You absolutely, positively, do not need much more than 300-350whp in a street driven daily driver. More than that, and you had better have a second car.

 

What is your current turbo setup?

I have a 1995 Subaru Legacy L. It has the JDM EJ20R engine in it paired with the JDM STI v3 5 speed and a limited slip rear diff. I have a Megasquirt stand alone ecu, port/polished heads, 252 cams, upgraded fuel pump, MSD, 660 injectors, front mount intercooler, rotated TD04, full 3 inch turbo-back exhaust, etc. I'm happy with my current setup, but its only good up until about 400awhp.

 

No TD04 is good for 400whp. Period. A TD04 is only good for, MAYBE, 215whp at best. If you want 400whp, you'll need much bigger than 660cc injectors, and you'll need something in the neighborhood of an FP Green or similar ~52-55lb/min turbo. Even then, on an EJ20, you'll be hard pressed to hit 400whp on pump gas. The USDM EJ20 bottom end is only good for ~330whp stock, before you start breaking things.

 

It should be noted, when considering a swap, the following:

 

1) If you turbo your existing engine, it'll probably break.

2) If you turbo your existing engine, it'll probably be slow.

3) If you don't do a complete swap from a turbo'd car, you'll have something unreliable to drive every day without tinkering CONSTANTLY. Expect to have your life dominated by your car.

4) If you do an EJ20 swap, you are wasting your time. With very few exceptions (like a twin scroll EJ207 or some other ultra-high-revving 2.0L with a twin scroll) the EJ20 is a waste of time. The USDM EJ20 sucks, and with the A/C ON, you'll get beaten off the line by a 2.5RS.

5) If you plan on doing a full swap, just buy a rolled STi. The end result will be much cleaner, much more reliable, much more durable, and much faster than any piecemeal hodgepodge you put together otherwise. If you REALLY want to have a turbo second-gen that you could actually consider marginally reliable, this is pretty much the best way to go.

6) If you DO plan on doing a WRX swap (EJ20 from a USDM donor), set aside funds to replace the EJ20 short block. Stock EJ20 heads on a stock STi shortblock with an 18G is a simple recipe for TONS of torque and lots of fun.

7) If you are going to do it, don't skimp. You'll regret every corner you cut when the car breaks down.

[broknindarkagain]

http://www.kk.org/thetechnium/house_of_frankenstein_revive.jpg

[broknindarkagain]

You can use a first generation Legacy Turbo subframe, and that will bolt right in. If you use the WRX subframe, you'll need WRX axles and control arms, or you'll need to put big washers on either side of your stock control arms to make up the gap. The WRX has wider bushings in the control arms.

 

I have the WRX subframe on my BD Legacy with no issues at all on stock Legacy control arms.

 

 

No TD04 is good for 400whp. Period. A TD04 is only good for, MAYBE, 215whp at best. If you want 400whp, you'll need much bigger than 660cc injectors, and you'll need something in the neighborhood of an FP Green or similar ~52-55lb/min turbo. Even then, on an EJ20, you'll be hard pressed to hit 400whp on pump gas. The USDM EJ20 bottom end is only good for ~330whp stock, before you start breaking things.

 

Nobody ever said that the TD04 will put out 400awhp. I should have been a little more clear on what I was saying. I'm talking about my block / heads. And the TD04 will give you more then 215awhp, I know this because I'm currently running a TD04 at over 215awhp (Dynojet tuned / tested). I was hitting numbers a little over 250 but tuned it back down to 230awhp.

 

And while you sit here and pick apart everything I posted, let me remind you the EJ20R is NOT the USDM WRX engine.

[Baddog]

I am not sure how if you turbo you're existing engine it will be slow?

 

I can see how it wouldn't be as fast or capable as a Turbo Motor.

[BAC5.2]

I know on the first generation cars, and on all model year Imprezas before 2002 the control arms were narrower than the WRX units. You needed washers to make up the space, or swap to WRX control arms. If the BD's have wider bushings, then that's a non issue.

 

You said your setup was good for 400awhp. That isn't true. On a USDM WRX, a TD04 is only good and reliable for around 215whp. More than that, and you are really pushing the efficiency range of the turbo and entering unsafe IAT and turbine RPM zones. You are begging for trouble if you push that turbo. If your motor revs beyond 6500, then it'll definitely make more horsepower. I'm telling people what they can expect for the swaps they'll be attempting.

 

I thought this was supposed to be a Turbo FAQ for the second gen? Not an "EJ20R swap FAQ". Some of the things you posted might only apply to the EJ20R, but most definitely do NOT carry over to the USDM EJ20. I was merely pointing them out.

[BAC5.2]

I am not sure how if you turbo you're existing engine it will be slow?

 

I can see how it wouldn't be as fast or capable as a Turbo Motor.

 

You can only run a few psi in a stock N/A motor. At 5psi, you are pushing the limits of the bottom end, and barely making stock WRX power. On an EJ22, you'll still be making less than a stock WRX. And both will be much less reliable than a stock WRX.

 

Slow is a relative term. It won't be as slow as it was stock, but it will most assuredly be slower than it would be if you did a proper motor swap. The cost benefit of turboing your N/A car is definitely negative. The power you'll gain doesn't even remotely balance out the reliability you'll sacrifice.

[Baddog]

You can only run a few psi in a stock N/A motor. At 5psi, you are pushing the limits of the bottom end, and barely making stock WRX power. On an EJ22, you'll still be making less than a stock WRX. And both will be much less reliable than a stock WRX.

 

Slow is a relative term. It won't be as slow as it was stock, but it will most assuredly be slower than it would be if you did a proper motor swap. The cost benefit of turboing your N/A car is definitely negative. The power you'll gain doesn't even remotely balance out the reliability you'll sacrifice.

 

I have heard good things about boosting the EJ22 on low boost with a good tune. But that is all hear say to me. I have read little problems on it. I have thought about doing it.

 

But I am going to stay away considering the engine isn't in as good of condition as it could be.

[broknindarkagain]

You keep talking about reliablity.

 

Its well know that once you start heavily modifying a car, it will NEVER be as reliable as it was when it was stock. On the other hand though, a car that has been built properly can be fairly reliable. Mine is a daily driver and has never had any major issues. Sure, there have been things that needed to be tinkered with here and there, but when I wake up in the morning and sit in the driver seat, I know my car will start and get me to where I need to go. Maybe I'll even have some fun driving it along the way.

[BAC5.2]

Low boost on a good tune is going to make MUCH less power than a stock WRX swap. If you consider low-boost to be ~3-5psi, then the TD04 is well outside it's efficiency range.

 

Remember. The first gen Legacy Turbo made 160hp and 180ft-lbs at 8psi. The lower compression of the EJ22T vs. the higher compression of the EJ22E would produce similar results at ~5psi on the EJ22E. You'd maybe get 175bhp and 190ft-lbs on your low-boost good-tune setup.

 

Is it REALLY worth the hassle for so little a gain? Definitely not, considering the ease at which a WRX swap can be done. You can buy a rolled WRX for as little as $3500. Plus, you'll get better suspension, better brakes, better ECU, and a better drivetrain. The USDM EJ20 is a bad swap, but it's a heck of a lot better than turboing an EJ22E, IMO.

[broknindarkagain]

BAC5.2, I will edit the original post to include some of the information you have posted...but it won't be tonight. I have to get to bed shortly, so I'll do it tomorrow.

[Baddog]

I have WRX suspension. WRX brakes. So it would be just for the engine. And even then. With all the broken 2.0's I see out there. I would pass on that motor.

 

I guess I will pass on any turbo swap until I find an EJ255/7.

[BAC5.2]

Keep an eye out for rolled STi's. There are some deals to be had, and that's a proper swap. You can usually make a bunch of money back by parting out the bits you don't use.

 

Cheap, Fast, Reliable. You can't have all 3.