Subaru Impreza GC8 & RS Forum & Community: - View Single Post - Boosting 1990-2002 USDM Subarus: A Chronological Guide
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Old 07-23-2010, 07:31 AM  
2.0L Turbo
Car: 2000 2.5RS BRP
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Originally Posted by joejoe69 View Post
Great write up man, I'd like to add a little from my experience as well.

The bold items are the keys to making this a successful build.

I want to stress on ignition timing control above all things when building these little shortblocks for boost. Ignition timing is originally high on these engines because they're specifically made for fuel economy, but when boost is in the mix, the result can be detrimental. In the old days of boosting these engines, pistons have melted and ringlands have cracked becuase of poor or no timing control.
True, sorta. Hot days, high boost, and bad fuel killed a few of them. All procedural mistakes, IMO. No intercooling and underfuelling is almost instant death. So is 85 octane gas.


The next thing is fuel quality and fuel support mods, relative to timing, which helps to achieve the correct AFRs and EGTs for boost.
Some think boost is indicative of timing when it's a reciprocal relationship. Timing also affects turbo behavior. I eliminate that notion with a blower. My .02.


Cooling, whether its upgrading your radiator, adding an intercooler in general or even a front mount, colder plugs, and an oil cooler. Remember, these engines weren't built for boost to begin with so try to extract as much heat out as possible in relation to how much power you make. Keep the engine lubricated internally at all times. More power requires more mechanical energy, more energy creates alot of heat. Reduce it.
Troof! That's what makes E85 work so well under boost. It can absorb heat all day long. Colder plugs transfer the heat to the head and the cooling system. Having the heat out of the combustion chamber is good but it always goes somewhere. Removing heat from the charge air and the combustion chamber makes for a happy Subaru.


Lowering static compression ratio helps give you some headroom for boost and is done by swapping heads as stated above and/or using thicker HGs.

Boost, the word we all love, is dependant on your tune and supporting mods. READ: If your tune and supporting mods CANNOT handle the extra air going in your cylinders, DO NOT, REPEAT, DO NOT turn it up and assume it will be okay because it won't!!

Lowering compression is an option but not a requirement. It's an option to relocate the throttle body, too. A Recirc valve is a requirement, IMO. There's work to do to make it to live and more work to run better. Timing is a factor in emissions, but I've always believed these motors like a lot of timing for torque. E85 works well with that skosh more timing that may have been harmful on 91.

Pump gas always seems to have these precautions to not make it angry. Ever notice that? You can't run too much charge heat, even though an octane test uses charge heat to piss off the fuel on purpose. Leaded fuel was developed against that kind of testing. You can't use too much timing and there's never much power to be had with it. Why does unleaded gas suck so much? E85's detonation resistance has saved my ass many times and performed where unleaded pump gas couldn't.

Glad to see some thinking going on. I wanted to post all this stuff before I got too senile and forgot all of it. All of these motors regardless of boost type have common issues like fuel quality, lots of timing, and higher compression.

Lastly, E85 fixes a lot but does create water in the crankcase on turbo cars. I never figured out why my n/a car didn't do that other than short emissions lines and direct vacuum.

Last edited by ImprezaRSC; 07-23-2010 at 07:34 AM..
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