Quote:
Originally Posted by Halon
ut there running greater than stock compression on e85, and what percentage of those turn to shrapnyl with the main cause being slightly higher CR?
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This happened and still does happen a lot when guys put 2G piston or similar compression pistons into a 1G and then try to run the kind of timing a stock 1G ECU does with 7.8:1 compression and maps meant for 12psi of boost.
Just because an RSX or S2000 or Audi or Evo motor can run it's higher compression with boost doesn't mean it is quite as easy with some old tech/shitty headed DSM or Supra. It's definitely possible and doable, but don't expect to be able to run as much boost as a lower compression car can on the same gas. Read that last line again, and then also realize that just because someone else on the interwebz has done it doesn't mean your setup will or that you can duplicate what someone else who is an expert at it and has tried all kinds of exotic setup has done. Yes, you can and will run less ignition timing on a boosted higher compression motor to avoid detonation, but you often get to the point where you have to pull so much timing that the gains are not there with more boost, or where you actually make more power at less boost with more timing.
Most people, not all though, run less boost on high compression setups. You will make more power with less boost though with higher compression. If your gas is not limiting you then it is definitely beneficial to run more compression. Higher compression is most useful for guys trying to set record with a limited turbo. Say you want to make the Evo 8 stock turbo HP record and you know that you can't run enough boost or add enough timing to max out the octane on E85 or E98 or whatever, then it can help quite a bit to bump that compression up to 10:1 or whatever and run the same maxed out boost as before but make more power. It is also a power gainer for guys who are limited to a specific size compressor inducer size or restrictor in drag classes or rally racing, any time the turbo is maxes or limited in some way. Guys who want better throttle response out of boost like for street driving or autox also often run higher compression. Higher compression does not spool a turbo faster though.
If you have a turbo/setup that is very efficient and can run high boost AND you are octane limited by your fuel, then you often can make more power with less compression, just because of being able to run a lot more boost while still maintaining a decent amount of timing advance. There are so many variables though that go into each setup that it can be hard to predict how each car will respond. Little things like exhaust housing size can start to become a major factor in knock resistance when you start try to push a fuel or run high boost levels. Usually every month I get a car or two for tuning with a setup that just doesn't work. We can't run the boost they want because something is making it too prone to knock and if we pull out enough timing to make it not knock, then it either makes the car misfire from too little timing or just doesn't make any power. That's life, engines are not like computers, they don't do the exact same thing with exactly the same parts.
In the NA-T thread, I have personally done something that they THINK won't work. I have gone from the 1.3mm stock TT headgasket in an NA 2JZ to a thicker Cometic HG because we were not able to make the power the customer wanted due to excessive knock. The car had an AEM EMS on it, so we were able to fully control timing. With the decently thicker HG were were able to run more boost, run more timing and make more power. It was also a road race car, and you need usually need to run a decent amount of timing with a rich A/F and keep your boost under control on a road race car. If you try to pull even a moderate amount of timing, like you can on a street or drag car, then you run this risk of melting the turbo. This is a 3mm HG
http://www.inlinepro.com/s1/p-52-inl...adgaskets.aspx
that is commonly used in the S2000 motor to drop the compression down ALOT for boost applications. Its massively thick, weighs a surprising amount and it works perfectly.
Anywho, 9.5:1 should be fine, just don't expect to run 40psi with it on E70.
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