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Boosting 1990-2002 USDM Subarus: A Chronological Guide
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Old 02-10-2011, 10:17 PM   #41
Chr1sM87
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yeah this info really helps. Almost got all the parts for my turbo build. Nice to have something to refer to for a little guidance.
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Old 02-11-2011, 01:26 PM   #42
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I see at the beginning it says 02+ isnt good for boost. But subaru ej wiki says there is different variations of motors between ej251..252...253 and they varies in year models from 99-04. What engines was reffered to as 02+. I have a buddy that just boosted his forester and im gonna use some of his downgraded stuff for my car...i miss my wrx....i have a 2000 forester but replaced engine with a 03 impreza rs engine whichs falls in grey area...

How can i tell which engine i have as of now... Just want to make sure what i have before i starting tearing into it..

stamping obviously says just EJ25?... Any insight would be awesome as i want to boost soon. 8Psi stock wrx turbo and ill be using VC2 and a msd boost timing master unit and FMU

Last edited by GENE-O; 02-11-2011 at 01:48 PM..
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Old 02-11-2011, 09:01 PM   #43
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If your 02+ EJ25 has a MAF, it's the 253. If it doesn't, it's a 251.
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Old 02-11-2011, 09:40 PM   #44
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Quote:
Originally Posted by GENE-O View Post
I see at the beginning it says 02+ isnt good for boost. But subaru ej wiki says there is different variations of motors between ej251..252...253 and they varies in year models from 99-04. What engines was reffered to as 02+. I have a buddy that just boosted his forester and im gonna use some of his downgraded stuff for my car...i miss my wrx....i have a 2000 forester but replaced engine with a 03 impreza rs engine whichs falls in grey area...

How can i tell which engine i have as of now... Just want to make sure what i have before i starting tearing into it..

stamping obviously says just EJ25?... Any insight would be awesome as i want to boost soon. 8Psi stock wrx turbo and ill be using VC2 and a msd boost timing master unit and FMU
I would advise against boost ON THOSE PISTONS, but could be wrong. Stick below 6psi. MY is more telling than the case designations in some cases. Unfortunately you are in that grey area. Invest in an STI block. It would be $1700 well spent. The problem with lots of these builds are the corners people cut in addition to lack of any specialized knowledge. Higher compression and boost is touchy enough without being undercut at the factory on the n/a parts. Some older stuff lives with precautions, but none of them are 500hp monsters. They just cave under high boost. Factory turbo parts don't. Complications still arise when you try to boost the 02+ factory n/a electronics with a boost-capable engine underneath it. That also still fails!

Invest in turbo components if you are looking to boost. Adaptation is a really, really strange thing with these cars. BTW, most Frankenstein combinations aren't really "healthy" under boost. All the ones I hear about that live have some special head machining or no boost. IMO, they don't have that certain "ceiling" after the sweetspot. They have their ceiling before their sweetspot and go boom. I hate to be the bearer of bad news, but a little more money goes a much longer way on the right parts.

Phase II SOHC engines should be in every classic engine-bay under a stock computer! My 110k 2.5L has gone so long more because I knew what NOT to do. The more up to date parts make better combinations even under the old electronics. Keep asking questions and I'll keep trying to dust off cobwebs.

I always loved SOHC heads. They are great to swap plugs on and have great midrange and revs. SOHC phase II heads on a 1.8 would kill compression, though. But, you could run a 2.5L SOHC combo in a stock SOHC Phase 1 ECU. Screwy shit like that is what I learned. Plan your strategies well to appropriately spend your dough. It's not always about who has more power. Good choices with the build do mean life or death to these combinations. Noobs in Subarus dig so far to find what they think they need. Most never reach a point of understanding how much they really don't need.

Little things changed so often in these, I stopped keeping up with it after a while. I saw under the hood of plenty of these older boosted combinations. The electronics were "Pong-like." Combinations were more like Legos. External controllers had dial-pots as opposed to software. The newer capabilities of reflashing still rely heavily on the older principles to tune the actual motor. Oversquare engines eat plugs. Boxer engines run hotter in the rings, AFAIK. Fuel quality is an inescapable requirement. I'm sorry I don't know the engine letters . If its any comfort, electric bugs really chap my ass. I hate those.

Here's another observation about the stock SOHC Phase II engines. They hate boost past 02+, right? But, they apparently LOVE E85 and even nitrous. 275hp on nitrous apparently lives for quite a while. Just because you use a "50 shot" doesn't mean you got 50hp from that nitrous dose. The same shot of nitrous on a better breathing motor makes more power. Fuel makes nitrous work. The same tricks for E85 and boost usage can also apply to nitrous.

Once you learn the little ins and outs of the stock components, you find a world of opportunities beyond just a "turbo swap." Subarus don't have that typical "full spectrum" of matured power technologies in the US. It's "been done" but not for decades by a huge bunch of people.

/rant
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Last edited by ImprezaRSC; 02-11-2011 at 09:46 PM..
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Old 02-13-2011, 06:13 PM   #45
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.....
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Old 03-28-2011, 09:00 AM   #46
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Would you consider an OEM wrx intercooler to be sufficient for <8psi on a 98' DOHC, AND, is running 91 octane (or above) mandatory when running 5psi (on the same engine)? I'm trying to price out the this, and when I look at premium gas prices I cringe.
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Old 03-28-2011, 09:55 PM   #47
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That OEM cooler would do fine, but there are better options. Fitment was always an issue as I understood it concerning the OEM tmic's to USDM stuff.

91 octane is mandatory for RS' even without boost. On 8:1 compression with 5psi it's not so bad because you aren't making the heat. 10:1 compression on 5psi makes a lot more heat AND hates more heat. It's the fuel that really can't take the abuse, not the motor.
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Old 03-29-2011, 09:08 AM   #48
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Understood. Have you a recommendation or two as to better coolers that could be sought after?
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Old 03-29-2011, 12:53 PM   #49
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Originally Posted by ImprezaRSC View Post
91 octane is mandatory for RS' even without boost.
incorrect, the ECU is tuned for regular gas, put 91 in there for long enough and you will foul your cat. If you added a turbo kit to an RS you might be able to get away with 91 just because the extra pressure would allow that fuel to burn better...just think about it 87 octane is still rich on an RS, adding a turbo would lean it out some, so 91 or 93 would prob be alright if you were turbo. If you aren't running a factory ecu you can get it calibrated for 93 (if you have it in your area) and just ue that gas.

Just saying from experience thinking I was getting "the good gas" for my car, when in fact I was running super rich and getting partially burned fuel resedue inside the waffling of the cat until it smelled like boiled eggs when i would be at WOT....so now I am making my own cat pipe because they are $300 a pop...so get some form of emanage unless you want to lean out when you get a turbo and possibly cause detonation or use 91 or 93 and have probs with idle or it just runs like shit.

Last edited by Xise; 03-29-2011 at 12:55 PM..
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Old 03-29-2011, 07:03 PM   #50
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You're also in here looking for an argument, so please knock that crap off and don't pollute the thread.

Some later model cars detonate and some don't even without boost. I will admit that. Detonation is a funny bug to chase on these cars and much more prevalent on the 10:1 motors. I tend to think they could be too lean with too much advance thus failing emissions and detonating at part throttle. NOx shouldn't be what it is on these cars, because CO2 and CO are always inline when it happens. There's a giant flyer by the checkout station at Denver emissions stations about high NOx on Subarus during testing. It's that prevalent of a phenomenon that something must actually be wrong, but really "what?".

Piggybacks also have unexplored uses on these cars. It's not all about "boost and turboz". No one has used a perfectpower as a nitrous controller or E85 supplementary injector, for instance (run with that, please. Not the scissors.) These things are thirsty by the nature of their design. A bastardized NA experiment at sea level is consuming 440s on E85 with a stock ECU. With a set of race heads and 12:1 compression, we're going to see just how thirsty it is. That engine will make in excess of 300hp with multiple throttles and should well drain 565 injectors.

Subarus are also bad about carbon, oil consumption, and factory fuel mapping. I also tend to think these cars consume oil because they are THAT hungry--it gets sucked in through the emissions system vacuum strength, and fouls the cat on the way out. The engine is the thirstiest 4 banger on the market.

The piston crowns also run hot, making the fuel more vulnerable to detonation. Run it lean and it detonates. The OBD2 ECU is smart enough to tune around dirty injectors, dirty filters, bad sensors, and dirty plugs as well as fuel type. 91 is at least playing good defense. There was 93 available when I first bought this car but not anymore.

/rant. There's more to those fouling cats and o2 sensors both than you think.
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