Cold Air Intake

[warnoldscu]

I have a stock Legacy Gt sedan and I just followed up on AEM's request for one of the new Legacy's. They want my car for a week to fit a cold air intake to the new Legacy's. I would like to do this if it's not going to be a problem, but I just wanted to know what you guys know about these. I've heard someone say that they might cause turbo lag, and I was worried that with the pipe all the way down low by the wheel-well that it might suck up water if the road were wet. Also, is this something that could mess with the warranty? Thanks for the help.

[BoxerGT2.5]

Will it mess with the warrany...probably not. Some WRX's have found to lose power due to the lenth of some ill machined intakes. Will you have to be cautious about water yes. If they are placing it outside the engine bay, but they usually use a rain sock for the filter element. I would say do it if they are willing to give you a intake for nothing. Won't hurt...if you don't like it pull it off...no harm, no foul. :)

[liquidiq]

On the WRX, the AEM made the car run a little leaner, creating more power. But it also didn't make it quite as safe, and it messed with the MAF readings. APS had a 70mm intake that would require tuning, but after working on it, they found that a 65mm intake housing wouldn't require tuning. The stock box is good for a lot of power actually, well, coming from the WRX.

[warnoldscu]

I don't know what it means to mess up the MAF readings, I'm guessing it's a computer thing... would there be a chip or computer tune or something that could fix this (if that is what MAF is)?

[BoxerGT2.5]

[quote name='warnoldscu']I don't know what it means to mess up the MAF readings, I'm guessing it's a computer thing... would there be a chip or computer tune or something that could fix this (if that is what MAF is)?[/quote] The actual length/diameter of the intake plumbing. The MAF sensor is the thin wire that sample the quantity of air and then the computer accounts for this in terms of how lean or rich you run. If you make the intake a rediculous length or diameter you will run lean beacuse the ECU will determine that not enough air is comming in hence it doesn't need as much fuel=lean. If there is one side of the spectrum you want to run on it is rich for the sake of the engine. When you design a intake they will most likely take air/fuel ratio readings based on different lengths and diameters and try and find a middle ground. I don't think you will loose anything doing it. Would be a good service for some cause they love the fact that very little gains are made from the intake alone; other than sound. After looking at the Legacy GT and comparing it to my Rx-8 in terms of intakes, it appears the Legacy intake is utilizing some form of Helmhotz resonant tuning. To answer your question..:) Yes they can reprogram A/F ratio's based on their intake....but it would never sell. Many just want a bolt on application with no tuning...espcially if the intake is the first thing someone does.

[awdG35killer]

well he lives in SoCal, the intake filter sucking up water should NOT happen. didnt happen to my se-r, and never to my friends lowered rsx-s(both AEM CAI). not many puddles around torrance/hawthorne, im there a lot. we appreciate your being the tester for aem, but if you dont know what the MAF is then it wouldnt be a good idea to be that person...only cuz if there was a problem you wouldnt know how to explaing it to us or aem. but GOOD LUCK anyways

[axis008]

AEM has (or had?) this thing that you can put midway on the pipe of the intake to allow it to allow air to be sucked up but not water. I don't remember what it was called but it seemed pretty genius.

[John M]

I can't see any potential benefit from a cold air intake. According to my logs, you get ambient temps in the stock intake as soon as the car is above 10-15 mph. Remove the resontator at the bottom of the airbox and you'll have all the cool intake you need.

[05USdmGTgUy]

The thing you speak of 1/2 way up the pipe is called a "water bypass valve" i believe. Personally , i would be more worried about a bigger intercooler/water sprayer. IMHO trying to lower the intake temp there(right before your motor injest's it) would be the most beneficial. However...I would be their test piggy if it got me a free cold air. Just cuz it looks and sounds cool. Mike...

[Guest JessterCPA]

Ya know, 05USdmGTgUY has a good point here. Does lowering the intake air really make a difference since the air is going through a turbo & intercooler anyway?

[Trent Bates]

Let me throw some "rules of thumb" out there regarding intakes. (Understand that these are very general and don't account for pipe diameters, proximity to sources of heat, etc.) It's harder to get air through 2' of pipe than it is through 1' of pipe, etc. A 90 degree bend is sort of like adding 3' of pipe. (Could that really be true?) Shiny surfaces reflect heat away better than dull surfaces. Chrome, and to a lesser extent White, reflects more heat away than Black. That's all I can remember for now. Perhaps I'll add to it later. I'm in agreement that finding ways to improve the intercooler's heat transfer abilities is where the focus should be. Also, the new plastic intake manifold is black. That's going to soak up some heat. Reducing intake temperatures by 5-10 degrees at most might not have any effect at all since it's got to run through the turbo anyway.

[Guest JessterCPA]

[quote name='Trent Bates'] Reducing intake temperatures by 5-10 degrees at most might not have any effect at all since it's got to run through the turbo anyway.[/QUOTE] My point exactly. Now ...how do we get that post-intercooler air temp down???

[05USdmGTgUy]

With the larger top mount that Perrin will release in 1-2 weeks. And/or a home-made water sprayer for inter cooler/or CO2/nitrous spray for intercooler. I will be doing the Perrin and a home made water sprayer that tee's off the windshield fluid(only at the drag strip.). Reducing the air temp. b4 the turbo will help but only minimally as the 20000rpm turbo creates ALOT of friction=heat. I will do the perrin cold air and inlet tube , but mostly for improved air flow , and bling factor. Mike....

[Drift Monkey]

I'll agree with the "pointless" argument. You're better off buying (or making) a water spray kit.

[Max Capacity]

Cooler air is more dense, carries more O2. You want to get the air at the Throttle Body as cool as possible. Granted for most of us we could tell the difference. But there is a reason for having an intercooler. Then adding something to keep it cool, water or CO2. Nitrous Oxide is also used.

[awdG35killer]

CO2 is better tho rught? i remember the VW guys using that, but it froze and cracked the piping around the SMIC...i hope we dont have that problem with our piping/hjoses

[rob]

[quote name='JessterCPA']Ya know, 05USdmGTgUY has a good point here. Does lowering the intake air really make a difference since the air is going through a turbo & intercooler anyway?[/QUOTE]Sure it does. Temperature rise out of the turbo is measured as increase over inlet temperature. Same with the intercooler, it's temperature drop from the IC inlet. If you start 15deg higher at the turbo inlet, it is translated to 15 deg higher going into the engine. [EDIT] You'll actually see a little more than the 15 drop after the IC because the IC does not have to work as hard to bring the turbo outlet temp back down to ambient (the air cooling the IC). So you will see 15 deg + 15 * (IC effeciency) drop. Hope that makes sense. -Rob

[Trent Bates]

BUT, Spending the money on getting cooler air prior to the turbo could instead be used to cool the air at the IC stage.

[John M]

Yes; 10 degrees colder in means 10 degrees colder out, and it's basically "free" horsepower. But, as I've already said in this thread, no aftermarket intake is doing to get you any "colder" air than the stock one does.

[05USdmGTgUy]

but, am i correct in stating that CAI's and inlet tubes will allow more +smoother air flow, which = more power. (and bling factor?) Mike...

[apexjapan]

Let me report on my own experiences, I think this will help. First, you cannot make a better "Cold" air intake than the stock one. Subaru did a fantastic job with the stock intake system, and it is perfectly designed to get air from the front of the car. If you get a CAI, you are giving up both colder air from the front and ram air effect from the front. However, ram air or pod air intake systems do have some benefits, along with some drawbacks. I used the AVO power air intake system for a while in testing, and the benefit was more power - especially with the avo piggyback to tune the a/f changes. The JDM 2.0 litre falls flat on it's face at 6800rpm, and with the power air fitted it would zoom to 7500rpm redline. Boost went up a good point. It was a bit noisy though. The drawback was a bit more lag. This would be more noticeable on the JDM 2.0-litre than the USDM 2.5 turbo, because the JDM makes peak torque at 2400rpm. It is designed to come in *real* early. It may not be noticeable on the 2.5, or may even improve. A carbon air box helped it a bit, but still, nothing beats the stock box for immediate response. However, if you are looking for mid to high rpm power increases, you will likely need to make some sort of induction changes from mild to wild, the stock system is designed to a very tight tolerance for the stock power setup. [b]But a higher flow panel filter would do more for people with stock setups than an induction kit would.[/b] Don't look at induction kits unless you are getting exhaust upgrades, and it would be really good if you were getting some sort of ECU tune as well, whether reflash or piggyback. Cheers, Paul Hansen [url]www.avoturboworld.com[/url] [url]www.apexjapan.com[/url]

[05USdmGTgUy]

You are the man Paul! Always have the knowledge and responses we need. Thanx Mike...

[awdG35killer]

so the cai would only benefit if i had a turboback and ecu?

[c_hunter]

Paul makes some excellent points. In fact, it's important to note that a dirty or highly restrictive air filter is going to negate the effect of almost any (or several) intake mods. So keep that in mind. As for the argument that cooler air going in equals cooler air coming out, well sort of. You also need to undertand the magnitude of the temperature rise across the turbo. A few degrees warmer or cooler in the intake is peanuts compared to the huge temperature rise across the turbo (and the consequent drop across the intercooler). Don't bother knocking yourself out for a few degrees reduction in the intake, it will be negligible compared to the temp changes across the turbo and intercooler. The biggest cooling effect will be from making the intercooler bigger and/or more effective. That's were temperature reduction really matters on a turbo motor. Also keep in mind that Subaru uses a resonator design in their intake (the "snorkus"). This tunes the standing wave pattern in the intake to increase pressure going into the system. In reality, what it does is create enough pressure rise to offset some of the friction and turning losses in the intake, so that the net system has very low overall losses. A lot of people remove the snorkus thinking it is a cleaner flow path, but that is not really beneficial to the stock intake. Craig

[apexjapan]

[quote name='awdG35killer']so the cai would only benefit if i had a turboback and ecu?[/QUOTE] Well, some sort of exhaust upgrades and an ECU. A CAI with an otherwise stock system would likely give you some hp at upper rpm's by leaning out the system, yet would also as likely take away some hp at lower rpms. Plus if the system changes are enough out of whack, the standard ECU may start compensating, putting you back to zero on gains and leaving the losses in place. This happened to me when I installed a Zerosports smooth intake pipe - early gains were great, and then in the end it made less power than stock. I swapped the standard piping in and gained enough back for my butt dyno to feel it. In comparison, high-flow panel air filters will likely give you a few hp gains only, but across the board. Plus they are much cheaper, much more reliable (other than the oiled filter vs. MAF issue), and far less likely to ever cause a problem with your dealer. Once you do have some ECU tuning in, though, a CAI would give some real hp gains, especially with enough flow out the exhaust end of your system. Cheers, Paul Hansen [url]www.avoturboworld.com[/url] [url]www.apexjapan.com[/url]