Could you safely raise the compression on an Evo to get more power off the turbo, or would detenation be too much of problem for a ratio of 9.5:1?

 

I my opinion that would be too high of compression on pump gas. Your tune would have to be right on & you wouldn't be able to run as much boost.

It would really depend on your set-up & what you are looking to do with the car, before I could recommend what compression to run, but I would not go higher than 9.1.1 at the highest.

If you want more off boost power get a stroker kit. Easier to tune and more torque....

Just my $0.2

 

The off-boost gains that you'd get wouldn't be enough to justify the smaller tuning window that you'd be limiting yourself to. You could probably still run stock boost on 93 octane but you're limiting your ability to run much higher than stock boost levels or take advantage of some of the rom tunes without the use of 100+ octane or form of alchohol injection. I personally wouldn't do it. A better option would be to increase the displacement of the engine. More off boost grunt without comprimising on boost performance. Just my 10 cents...

 

You won't be able to run increased compression without dropping boost levels, which means you'll be making less power.

The only reason to raise compression is to give better off-boost response in normal driving, and I doubt you'd find the tradeoff would be worth it.

 

It also depends on turbo as well because if you use other than stock turbo like gt30 and raise compression to 9:5 probably be a pretty good combination. different efficiency range. hondas do it all the time low boost 10:1 compression sc61 etc. My old car had a
60-1, 9psi wastegate spring, 1.8 liter motor 10:1 compression and put out 343hp on 9psi

 

Yeah, it's popular in the honda world. My old turbo si had 9.7:1 compression pistons and made 365whp on straight 93 pump with 10 psi. It does make the car harder to tune though, and will increase your chances of detonation. Like Ted B said, the off boost power would be a little better, but I doubt it would be anything significant.