What is your Opinion on the "right" compression?

[-435-]

Hey Tuners,

Im not really "new" here just forgot the password to my other account and dont have the email to it anymore -_-

But anyway I have acquired a used 6 bolt motor. I know nothing of the history to this motor so I'm going to rebuild it completely. I'm thinking once I get a shell etc, etc together I will be wanting to sit at about 400-450 AWHP. Turbo will be HX35 or another of similar size. Boost will be running around 25-30 PSI. So my question is what would be a good compression ratio for my goals in you're (The Tuners) eyes.

 

[My1GLaser]

9:1 FTW!

No issues when I was running pump gas on an 18g at 26-28 psi. 18* timing, and probably about 400 whp. It took some work to get coolant temps & IAT low enough to push my set up. Now I'm running an HX-35 on E-85 at 35 psi and 22* timing and I love it.

Pay attention to the details on the build, polish the CC, no sharp edges, proper quench, etc.

 

[JusMX141]

Compression doesn't matter as long as you're willing to run a lot of boost.

Sure high compression will extract the most power from the airflow that the turbo is generating, but it also requires a much higher-quality fuel than low-compression does. So ask yourself if you're willing to run race fuel or E85 as compared to pump gas to get to your horsepower goal, then you'll have your answer as to what compression you're looking to run.

 

[bastarddsm]

If your gonna run E85 all the time 9:1+, if you will run pump gas your best off to be 8.5:1 or less.

 

[-435-]

Unfortuntly the clostest E85 Station to me is in Nevada, so chances are I'll be running 93 octane fuel. So what Im gathering is the lower the quality the fuel is the lower the compression should be in a sense and visversa for high quality fuel?

 

[Bud92gsx]

Pump gas and meth injection may be in your future.

 

[-435-]

Pump gas and meth injection may be in your future.

Now thats a compromise I can live with! Im actually runing a Meth kit on my power stroke but using winter windsheild fluid with a rust inhibitor. Would that be ok to run through a gas engine?

 

[bastarddsm]

With only pump gas in your future, I'd go for somthing like 8:1, and a good intercooler.

 

[Bud92gsx]

Meth is like 8 bux a liter at menards.Mix 50/50..Or buy cases of heat.

 

[-435-]

Thanks for the answers and suggestions! Now I just have to decide whether or not I want to run meth then that will lead me to what compression I'll be running. Again thanks everyone.

 

[JusMX141]

Unfortuntly the clostest E85 Station to me is in Nevada, so chances are I'll be running 93 octane fuel. So what Im gathering is the lower the quality the fuel is the lower the compression should be in a sense and visversa for high quality fuel?

Correct.

Low-octane fuel burns fast and hot, high-octane fuel burns slow and cool. The lower the fuel quality and higher the compression, the more-prone the car will be to experiencing incurable knock when attempting to run lots of boost.

 

[-435-]

Correct.

Low-octane fuel burns fast and hot, high-octane fuel burns slow and cool. The lower the fuel quality and higher the compression, the more-prone the car will be to experiencing incurable knock when attempting to run lots of boost.

Ok, that makes sense. What excatly is knock? I know its something to avoid, but coming from the diesel world its nothing I really have ever had to worry about so Ive never learnt.

 

[StarFawkes]

Detonation.

http://auto.howstuffworks.com/engine-knock.htm