The ultimate forged piston longevity thread

[MyMomsOutbackXT]

Okay so there is many articles and forums out there stating that forged pistons decrease engine longevity due to the piston slap you get on startup. But how much of a difference it makes is really largely up for debate, so I figured, with a collection of car enthusiasts where installing forged pistons is basically a right of passage as big as the subie community, it would be a waste not to pool all this data.

 

 

So my question is, how far did your engine run/has your engine run with forged pistons? At how much HP? Which brand were they? Which size? and how hard do you drive your car? The Poll provides nice general info but I'd love to get some more detailed responses. Let's get to the bottom of this!

[BrandonspecB]

Honestly, the best answer isn't going to come from anybody here or any forum. Get in contact with both IAG and Outfront Motorsports and ask them. I'd have to guess together they build hundreds of forged EJs every year.

 

They'll have a pool of data and experience big enough to give you what I would call true information.

[MyMomsOutbackXT]

Honestly, the best answer isn't going to come from anybody here or any forum. Get in contact with both IAG and Outfront Motorsports and ask them. I'd have to guess together they build hundreds of forged EJs every year.

 

They'll have a pool of data and experience big enough to give you what I would call true information.

 

Good thinkin. I sent them an email. Only reasons I didn't send one earlier is because I'm expecting the answer to be "Depends on how the car is driven/maintained. Can't give an estimate" and that's that.

 

The reason I came to the forum is I was hoping for a large pool of info, so that me and any others with the same question can find people with a similar build/maintenance habits/diving habits and extrapolate an estimate from that.

[boxkita]

I have a v2 outfront closed deck block with forged pistons, clearanced to 35 over. I put 29k miles on the engine at the track and street. Piston slap is a thing until warm, however, Its not for me. I idle until engine is low-end of warm, then ease on out until actually at operating temp. From then on, I tend to be in 3000-5000 rpm range. I changed the oil when it got dark, probably averaged every 1000 miles. I used chevron 15-40 turbo diesel non synthetic oil. I got a blackstone analysis every 5000 miles to check. On track, I ran slicks. On the street, I ran Michelin SuperSports. Replaced street tires every 7500 miles.

 

If you previously drove a honda or some other vehicle that allowed you to start and go, your forged engine build isn't going to be a fun experience. Expect longer warm up time and more regular oil changes also a better gas choice.

 

For the average owner, forged is not needed. If 90% of your driving is just driving stop go normal stuff, forged is a waste of money. One of the supporting mods is a custom tune and a good cooling system.

[boxkita]

Good thinkin. I sent them an email. Only reasons I didn't send one earlier is because I'm expecting the answer to be "Depends on how the car is driven/maintained. Can't give an estimate" and that's that.

 

The reason I came to the forum is I was hoping for a large pool of info, so that me and any others with the same question can find people with a similar build/maintenance habits/diving habits and extrapolate an estimate from that.

 

with a moniker of "mymomsoutbackxt", I'm guessing you're not the target audience of forged pistons. If you are, get the closed deck upgrade with your forged pistons.

[MyMomsOutbackXT]

with a moniker of "mymomsoutbackxt", I'm guessing you're not the target audience of forged pistons. If you are, get the closed deck upgrade with your forged pistons.

 

Haha nah my username is just a joke since an OBXT is kinda a mom car. I'm shooting for 400whp, and the car isn't my DD. (Yes I have read the "are you sure you want 400whp" threads). Don't quite trust the type RA pistons from the shortblock I bought. But also don't wanna throw in forged slugs for the block to only last 20k miles.

[MyMomsOutbackXT]

I have a v2 outfront closed deck block with forged pistons, clearanced to 35 over. I put 29k miles on the engine at the track and street. Piston slap is a thing until warm, however, Its not for me. I idle until engine is low-end of warm, then ease on out until actually at operating temp. From then on, I tend to be in 3000-5000 rpm range. I changed the oil when it got dark, probably averaged every 1000 miles. I used chevron 15-40 turbo diesel non synthetic oil. I got a blackstone analysis every 5000 miles to check. On track, I ran slicks. On the street, I ran Michelin SuperSports. Replaced street tires every 7500 miles.

 

If you previously drove a honda or some other vehicle that allowed you to start and go, your forged engine build isn't going to be a fun experience. Expect longer warm up time and more regular oil changes also a better gas choice.

 

For the average owner, forged is not needed. If 90% of your driving is just driving stop go normal stuff, forged is a waste of money. One of the supporting mods is a custom tune and a good cooling system.

 

I do of course plan on allowing my car to properly warm up, using Motul 5w-40, and doing oil changes every 2-3k. Wouldn't be pushing 400whp all the time, but would want to be able to do it every now and again without fearing the block will blow up after every pull.

[awfulwaffle]

The more experience I get with this platform, the more apparent it becomes that even at moderate power levels, it's crucial to get a quality tune and keep an eye on things after the fact if you go deep into upgrades. These aren't hands off cars, forged or OEM internals. I know it probably seems obvious, but even a good forged piston will come apart at 300 whp if you treat it poorly or miss a sign of some issue resulting from a mod.

 

This is the #3 piston out of a friend's FXT I have sitting at the shop. Motor is an IAG Stage 2 Tuff shortblock, car was built by an IAG authorized installer. Cryotuned, so quality tune. Drove beautifully for the first 30k, then one day bam, no boost, blowing oil smoke after a pull. Still need to dig in and do some forensics, but it seems it detonated pretty good and initial suspect is a failed injector (big sidefeeds). Owner had noticed a misfire intermittently at idle, but that was chalked up to older coilpacks and left alone. Maybe we'll find that it was signs of a failing injector that got overlooked.

 

Long winded way of saying, at the power levels you mentioned it's more important to get a quality tune, good parts, and to keep an eye on things down the road once the car's running. I have data up full-time via BtSSM for this reason in my personal car, address issues immediately. Have caught a catastrophic failure in progress twice now.

Edited March 21, 2021 by awfulwaffle

[BrandonspecB]

"Depends on how the car is driven/maintained. Can't give an estimate"

 

I would think this is the right answer. It applies to any engine, even a factory assembled RA short block.

 

My friends say Subarus are shitty cars because they're the only ones that require a new short block as part of regular maintenance. They're right though. Go look on ksl.com at used WRXs and it's hard to find one that hasn't had the engine replaced.

 

I tell them though that it isn't the EJs fault. I made 450 whp on a stock, unopened 110k mile EJ. It did eventually break. It wasn't the rings or pistons that failed. It started pushing coolant under power. Head bolts failed.

 

There's is a certain type of person attracted to turbo Subarus and they don't drive their cars easy nor leave them stock. Combine that with the emissions/economy centric factory tune and you have piles and piles of broken pistons.

 

The only way to find the info you want is to build an EJ with forged pistons and drive it like grandma to see how long it lasts. All other instances are going to be diluted with high horsepower, high rpm, and racing. Those contribute far more to engine wear than the material they're made from.

 

I've had a few forged pistons engines, but they always break before the pistons wear out. These engines weren't in my daily, so they don't accumulate a lot of mileage. The longest I made it was 40k and the pistons and cylinder walls looked amazing. I was honestly shocked. 500+ whp 7500-8000 RPM it's entire life. That engine actually was daily driven for a few years and went to the track often. If it wasn't dailied it probably would have had only 10k miles on it before it popped. That really was my fault though. I pushed that engine further than it was built for.

 

I think you should look into some 4032 forged pistons. When OE manufacturers use forged pistons that is the alloy they use. They have more silicon than the usual 2618 piston you see and expand/contract less. You can get away with tighter clearances and still have more durability than stock. In fact, a 2618 is really only needed for lots of power and heat. A car that is daily driven 95% of the time probably doesn't need one.

[shralp]

If you have that power on tap you’ll use it every chance you get, let’s be realistic here . You’re right IAG or Outfronts reply would undoubtedly be just what you expected. That’s the proper answer though. Your really not going to get any useable data from this survey because it’s not just about those using forged and those not. If someone dropped in forged pistons but did the install improperly then they will fail early. If they abuse the motor or have less than ideal OCI’s it will fail. There are just too many variables in this picture to get an accurate data set. Not what you want to hear but it’s kinda the reality. If you really want 400 to the wheels and have it be somewhat reliable, I’d suggest sourcing a local Suby builder that really knows what they are doing work with them or source a properly built short block a la IAG, Outfront, or Rallispec. They will be a much better wealth of knowledge to help you select something that can handle the power and give you longevity you seek. Just know that it’s going to take a cohesive package beyond forged pistons to get you there. ...and it’s gonna cost if you want it to last. Edited March 21, 2021 by shralp

[shralp]

I second what BrandonspecB said and will throw my hat in the ring for 4032. I’m currently running Rallispec’s Cosworth 4032 pistons in their “street value” short block (they may have changed the name over the years). It’s in my ‘05 track car and while it’s street legal I don’t drive it much on the streets. I do however drive that absolute piss out of it on track as much as possible each season. It’s been fine thus far and I think I’m on season 6 with it

[boxkita]

for your stated intentions, Id skip the forged pistons. not a daily and occasional pulls isn't goi to put much stress on components.

 

"People race them all the time"....not really. the factory race teams rebuild the engine every 400 miles or so. They change the oil after every race. They use custom built blocks at 750k each, you can get the wilall billet for 15k which is about the same.

 

"my buddy has 400hp..." In the Subaru world, any description of a car that includes those words is automatically bogus. Just walk away.

 

"I'll do regular oci". really means you'll be doing regular rebuild/ynansb. Going forged and high hp means you'll be treating every component like its on its deathbed. You can flog the whole but you'll be replacing components on a regular basis. The race wagon has 11k actual miles and has had several ynansb incidents. Regular oci means you should be checking oil color and consistency on a regular basis and changing it frequently. On a typical track day, I changed it before and after. The after smelled horrible. Keeping the oil fresh and in condition is a key component to the engine survival.

 

"I did my engine build in my basement and used an ots map". that engine is hanging in the noose and the lever is in motion. You could be one of the lucky savant builders who gets a great build with your pile of components. Like powerball, the odds are against you. A professional build by a competent high power builder using their component list tuned by their recommended tuner list is going to get you the best possible outcome. The more you mess with that formula the more risk of failure you have.

 

"my build was only 4k..." Idk what everyone else spent, and I'm not the highest; but it was 'gulp' money for the build and more dollars for the tunes. If you don't have a tuner onboard before you start, you're going to be frustrated. The builder and tuner having experience with each other or at least each other's system will help considerably on achieving your goals. If you don't have goals ( you didn't list them so going with none), your build/tune is going to be expensive/not much long term fun. ymmv.

 

400hp subaru engine is the entry point for big dollar builds. No used parts here. No pcpartpicker here. You can build, literally, your experience an engine at a time until you get what you want or pay experts to build you a good solution. Your still going to have a race engine so maintenance will be on you unless you live next to the shop that built it and they are diligent in their maintenance ( if any person associated with the shop smokes/inhales/alters, you probably want to find a place where their primary pleasure comes from kickass subaru builds).

 

Lastly...asking for a poll to get a history for other folks? what other folks? building a forged engine isn't a "how many likes can I get to buy x component"...well it could be a predecessor to "watch me blow up my 2 hours old forged engine on the dyno" yt. In general, especially on this forum, ppl looking for forged engines, tend to be solving a problem after an engine failure that didn't come from poor maintenance or bolt-on part selection failure. The engineering and agonizing over the choices is part of the forged experience. As suggested by several others, you want forged? Look up the big 3 and pick the package you want. Contact a tuner (several frequent this forum) and tell them you are looking at x shortblock package and ask how the tuning goes and if there's a local builder they work/worked with in your area. Depending on where you live, you might be better off to haul your car to a reputable shop and hand them a blank check. I'm not ashamed to say I did that. I'm pissed that their dopehead maintenance mechanic missed the mechanics rag in the radiator that led to the hg failing after 1000 miles. ymmv.

 

At this point in the lifecycle of the EJ, making 400hp is a well-known formula. Making it last is also well-known. Getting off the beaten path leads to money pits.

 

For an occasional pull build, I'd do a regular 300hp build and skip the forged experience. Spend the savings on gas and tires and brake pads. With a large area tq tune, you can have "get arrested" fun in any gear.

 

the engine rebuild section has alot of builds in it. usually they link to the startup and occasional followup checkin posts. worth reading.

[boxkita]

Wouldn't be pushing 400whp all the time

 

only if your tuner set it up so 400 was at redline.

 

If your tuner put 400 at 4000 to 5000, you'll be dropping out of 5th gear all the time and running in 3rd gear. Unless you were smart and put in the 6mt to begin with. At which point you'd be in 3rd or 4th depending on which set of gears you upgraded to. 400hp will destroy the 5mt's 5th gear in no time. The 6mt's gears aren't glass but 400hp can be hard on gears if you don't shift properly. ZF in colorado is pretty much the goto shop for transmission builds in conus.

 

Given you have the same locale as brandonspecb, id suggest a pm to find out who did their builds. Contact the shop and ask for a "lessons learned from brandonspecb" build. The build will probably be 10-25k by the time you are done because 400hp requires replacement of just about every component of a 16yo car. 10k if you get lucky. 25k if you try to help.

Edited March 21, 2021 by boxkita

[BrandonspecB]

Lots of good info here.

 

To OP: I had to sort of make a shift in how I see an engine when I started trying to squeeze them for all their worth. I had to start seeing the engine as a wear item. I see the Outback isn't your daily. That's the first step. Having a dedicated daily takes away a lot of the stress of building a power dense engine.

 

400 whp EJ is ~500 crank hp. 125 hp per cylinder. In a tiny aluminum engine. EJ short blocks are little. They move all over the place when you torque the mains and heads down. This is probably their biggest weakness for big power.

 

Is there even a stock 500 hp 4 cylinder from any major automaker? I googled it and couldn't find one. That says a lot.

 

I'm not trying to talk you out of this. Just trying to make sure you have realistic expectations. 400 in an Outback would be fun. I know how fun it is to put the hurt on an M4 as he tries to come around on a freeway on ramp. Not today buddy. Not just a little hurt either. Lots and lots of it. So much I think he thought his car was broken. I think some people don't believe their eyes when they see a Legacy accelerate like that. And then doing it in an Outback...damn. Just make sure you whoop ass on Beemers responsibly.

 

So about what boxkita said...I've had my engines built at Metric Motors in Centerville. They've been doing Subaru engines for a long time. If a dealership around here is having a Subaru engine or heads rebuilt Metric is probably doing it. If I remember right, when Cobb was located here they had Metric build their engines. They've got EJ torque plates all over. But they're really busy right now. They're main engine builder got seriously hurt in a dirt bike accident last year and is just starting to get back working. He's friends with my friends and is well known in the drift community around here. You can call and talk to Chris about a build. He's the owner and is very knowledgeable. They can build an engine to whatever spec you want. You'll probably be waiting at least 2 months from the day you drop your stuff off.

 

Tuners around here...I honestly can't say. I don't do social media so I'm not in any of the local Subaru circles. When people ask me to tune a Subaru I send them to Simple Performance. I met their tuner when I had my car dynoed at Ziptie Dynowerks. Ziptie is shut down and now he works at Simple. Haven't heard anything bad about them, but I'm not the best to ask.

 

Some advice. Pick a tuner and ask them what setup they know will work for 400 whp. Injectors, fuel pump, turbo, intercooler, intake, etc. Tuners don't like trying to work around shitty mechanical parts choices. Ask them what works and buy it. I would also recommend installing an oil pressure and fuel pressure sensor that can be data logged. You won't need your TGV inputs or your rear o2. So that's 3 inputs for your wideband, oil pressure and fuel pressure. Trust me on this. Making sure fuel pressure does what it's supposed to is so very important. I'll post up some graphs of a lean out that broke an engine and then some graphs of fuel pressure when I got a new engine and started figuring out what happened. Look up the how to on this forum about rewiring your fuel pump control module. This is so important.

[shralp]

I'll just leave this here

[xt2005bonbon]

Is there even a stock 500 hp 4 cylinder from any major automaker? I googled it and couldn't find one. That says a lot.

 

 

Looks like 416 BHP is the max at the moment from AMG.

 

--> https://www.caranddriver.com/news/a27813840/mercedes-amg-m139-four-cylinder-engine-specs/

[boxkita]

I'll just leave this here

 

motoiq builds an sti. >25k build. wpc treatment would be close to $1000 alone.

[boxkita]

Looks like 416 BHP is the max at the moment from AMG.

 

--> https://www.caranddriver.com/news/a27813840/mercedes-amg-m139-four-cylinder-engine-specs/

 

I just started working at a Mercedes dealership as a tech. The first car of the day was one of these engines. I might have geeked out a bit. No oil leaks, no drips, no burning smell; my brain might have melted a bit.

[BrandonspecB]

Here's what broken engine data looks like. I was using Accesstuner to tune. This engine had 40k miles. Cylinder two cracked and bent a rod. Piston came out just fine surprisingly.

 

I had made some changes to my meth injection nozzles hoping to lean out the meth injection just a hair. Trying to figure out meth nozzle sizes can be a pain because different manufacturers rate them at different pressures. I miscalculated and got the wrong ones. What I found is that my meth injection system was covering up a lean out from the primary fuel system and once I put smaller nozzles in the problem revealed itself.

 

34 psi of boost. As soon as the turbo came on I felt the engine shudder. You can see from the feedback knock the ECU was pulling timing, but couldn't do it fast enough. Damage was done from the massive lean out. A fuel pressure or lean out protection would have saved this engine. Knock sensors can't save an engine from massive detonation.

 

Once I got a new engine together I wired in a fuel pressure sensor to one of the TGV inputs I wasn't using. At lower boost levels there wasn't a problem, but once I started turning the boost up it was clear fuel pressure couldn't keep up. Huge lean out at high RPM in the second graph from fuel pressure dropping.

 

The factory FPCM and wiring weren't allowing enough voltage to the pump. I bought an older STI FPCM and rewired it from the battery with 12g wire and problem solved.

[MyMomsOutbackXT]

Not sure if any of those that replied have subbed, but I'll hope you all have because I'd like some feedback.

 

I'm thinking of maybe just shooting for 350whp instead. If I do this, would I be fine on the regular 'ol Type RA pistons? They're already out of the block, and I already have the forged pistons at my house. But I don't want to put in forged pistons that aren't gonna last if I'd be fine on the stock pistons.

 

If I do use the Type RA pistons I'll open up the ring gap of course since they're already out of the car.

 

If I swap in forged pistons and still keep it at 350 whp, would the block last just as long despite expansion issues seen with forged pistons?

 

Basically the car will be a weekend car, but I'd like to drive it nice and hard on the days I do take it out. Canyon runs, flexing on friends while we cruise, etc. Don't wanna feel like I have to baby it while driving. That being said, maintenance wise, it will be babied. Always fresh oil, won't stand for any kind of leak or CEL without fixing it before the next drive, etc.

Edited March 26, 2021 by MyMomsOutbackXT
Wrote 500whp instead of 350 lmao oops

[boxkita]

In my experience, which to be fair, includes more cars sitting on flat tires than being flogged; a well-built subaru engine should last 30k of serious thrashing. Assuming the maintenance is rigid, thorough and preventive.

 

My first engine blew because head gasket failed. 2nd because oil starvation. 3rd because stoner mechanic messed up. 4th because newbie mechanic forgot head gaskets. 5th is still on engine stand until I can clean the grinding grit out of it without tear down. 6th has been waiting on a oil change for nearly two years (boxkita died and his wagon has been sitting ever since).

 

Of all of those failures, forged pistons would have prevented zero. Do I believe forged pistons kept the track car engine alive for 30k, yes, but there's everything else that went with it. Forged pistons are race car. If you are going to do race car, then don't half-ass it. I bought the best available at the time. Idk if I'd do it this time (billet forged, coated, wpc'ed, cryo'ed, etc); seems overkill now. Then again I'm not barely 40 making stupid money and just starting my lifelong dream of becoming Michael Schumacher.

 

Your goals seem all over the place. canyon carving, dyno pulls, flexing, weekend toy? I'd pick canyon carver and build that. Everything else would work too. You'd spend really good money on great suspension parts and tuning, good money on a decent engine (yer not gonna live long with an 8000rpm 350hp engine on mulholland drive), probably crazy money on jdm interior parts & ice.

 

A stock lgt running new oem specb suspension bits, well setup coilovers (ohlins?), lgt brakes with autocross pads, a 6mt with specb gears, and a really good tune would be an awesome car. Learning to drive it at the limits would require a serious investment in quality summer tires. If could keep the oil where it belongs and the heads/top of pistons cool, the engine would probably last a long time.

 

I still think you're going at it expensively. Make a 4 item goals list (how many miles will last, how big is your budget, how rigorous will you maintenance be, what's most important thing you to use it for). Then find a tuner who think that list sounds like the most fun they'll ever do. Then work on a parts list. That's what I did.

 

Forged pistons? I used 2xxx because racecar. I hate waiting for it to warm up...literally sounds like a diesel on its last legs. Warmed up? its pretty quiet. Video in my link is not my fastest laps but its not slow either. That's all the noise there is.

[norutah]

In my experience, which to be fair, includes more cars sitting on flat tires than being flogged; a well-built subaru engine should last 30k of serious thrashing. Assuming the maintenance is rigid, thorough and preventive.

 

My first engine blew because head gasket failed. 2nd because oil starvation. 3rd because stoner mechanic messed up. 4th because newbie mechanic forgot head gaskets. 5th is still on engine stand until I can clean the grinding grit out of it without tear down. 6th has been waiting on a oil change for nearly two years (boxkita died and his wagon has been sitting ever since).

 

Of all of those failures, forged pistons would have prevented zero. Do I believe forged pistons kept the track car engine alive for 30k, yes, but there's everything else that went with it. Forged pistons are race car. If you are going to do race car, then don't half-ass it. I bought the best available at the time. Idk if I'd do it this time (billet forged, coated, wpc'ed, cryo'ed, etc); seems overkill now. Then again I'm not barely 40 making stupid money and just starting my lifelong dream of becoming Michael Schumacher.

 

Your goals seem all over the place. canyon carving, dyno pulls, flexing, weekend toy? I'd pick canyon carver and build that. Everything else would work too. You'd spend really good money on great suspension parts and tuning, good money on a decent engine (yer not gonna live long with an 8000rpm 350hp engine on mulholland drive), probably crazy money on jdm interior parts & ice.

 

A stock lgt running new oem specb suspension bits, well setup coilovers (ohlins?), lgt brakes with autocross pads, a 6mt with specb gears, and a really good tune would be an awesome car. Learning to drive it at the limits would require a serious investment in quality summer tires. If could keep the oil where it belongs and the heads/top of pistons cool, the engine would probably last a long time.

 

I still think you're going at it expensively. Make a 4 item goals list (how many miles will last, how big is your budget, how rigorous will you maintenance be, what's most important thing you to use it for). Then find a tuner who think that list sounds like the most fun they'll ever do. Then work on a parts list. That's what I did.

 

Forged pistons? I used 2xxx because racecar. I hate waiting for it to warm up...literally sounds like a diesel on its last legs. Warmed up? its pretty quiet. Video in my link is not my fastest laps but its not slow either. That's all the noise there is.

310/300 at 4300' and ambient temps of 88°.

NPR pistons, nitrited STI crank, full killer b oil, 12mm pump w/ cosworth mods, GSC valves, ARP studs, all GS pre and post turbo/hot and cold side-all gasket matched and ceramic coated, fluidampr pulley, DW 740 side feeds and pump. VF52 and turbolab maps. This is a simple no BS set up that didn't break the bank. I know my 5mt limitations so power goals were modest. I put a lot of time and $ into suspension and this thing is a blast in the canyon. The future likely holds PPG synchro gear set and slightly increased power levels--wherever the car is happy. The baseline pre-dyno map caused us to abort first run as it was heading in the 330 range. Joe said it was very happy there and I kinda think that's where he wanted to take it but again... Stock 5mt and because driven like a teenager

 

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