Opinions on Compression Ratio

[ndedomin]

I plan on upgrading my engine internals in the near future to lead the way for a turbo upgrade and other power upgrades which I want my engine to be ready to handle without breaking anything, but I am confused about one thing.....the compression ratio of the pistons. I know a lower ratio can help prevent knock and a higher ratio is technically more "efficient", but what do you all think is the better route to go on these cars? 9.5:1 or 8.8:1??

I'm curious to hear what you all think before I go out and make the big investment on the Arias Pistons and Pauter Rods, etc.

 

[FrequentFlyer]

The problem with going lower is that off-boost performance will suffer a bit. Depending on which turbo you go with and how much lag it has, this may not be what you want. I would stay at 9.5:1 and use meth and a good tune to eliminate any knock. Being direct injected, I think that with the fueling mods on the horizon for this car (CDFP's), a standback and meth, you won't have a problem with 9.5:1. Coming from the S2000 community, I've seen guys put turbos and superchargers on a car with 11.0:1 compression ratio without problems, granted lower boost levels. Huge power gains from throwing a blower on a car with 11.0:1 motor that flows well (100whp over stock at just a 7psi T04E/T3).

 

[ndedomin]

Thanks for the advice. That's the direction I was leaning, so I think I'll stick with your thoughts and my gut feeling and go with the 9.5:1 when I do this. I'm also going to make sure I have my engine management, a better fuel pump and meth set up as you suggested. The next thing I am ordering is actually going to be the CP-E Standback and PnP harness. A fuel pump would be in the works soon after that. Thanks again for your response!

 

[FrequentFlyer]

And if I may add, it really depends on your ultimate power goal. If you're just looking to put on a G3071R and can live with 350-ish whp, again, I don't think9.5:1 will be an issue. If you're going to put a 76R on it and run 25psi, you may want to go lower, but again, bigger turbo, later spool, crappier response out of boost with lower CR. It's give and take. If you're building an all out 1/4 mile car and want low ET's and high traps = big turbo. Daily driver and reliability = 71R IMO.

 

[ndedomin]

yeah, the 3071R is the turbo I am eventually going to install....I'd rather have the quicker spool. I'm looking to get to 350whp as my final goal in terms of power, so that should be more than enough for that. My car is not intended to be a 1/4 mile car. Instead, its more of an auto-x and track (i.e. VIR) car, so quick power out of the turns is important to me. It is also my daily driver. I think the 3071R with the proper attachments, internals, and tune, should be more than enough for what I plan on doing.....and as I said, I prefer the quicker spool.

 

[redspeed]

You will make MORE HP from going low C/R with higher boost. More boost= more HP. Not the same with high C/R. You will seriously limit the amount of boost you can run w/out flooding the engine with meth. The MS3 has plenty of torque so no worries there.

Just my .02