Re: high or low comp pistons
 

Yes, it's all about the octane and timing.

With pump gas you'll want go with a lower compression, with race gas or e85 you can use a higher compression.

If you try to use low octane with high compression and high boost you'll have to pull a ton of timing, that will cause high EGT's and it will be inefficent at making power.

Re: high or low comp pistons
 

Good points brought up... One more thing, as far as I know a lower CR would make it feel more sluggish when not in boost - which would bug the hell out of me in a street car. Just something to think about... I probably wouldnt go below 9:1 in my car

Re: high or low comp pistons
 

I wouldn't go lower than 9 to1 it wouldn't have power off boost. :8

Re: high or low comp pistons
 

my friend has 7.1 in his dsm and it hits 36 psi no problem not laggy

Re: high or low comp pistons
 

i'm running 9:1 cr pistons with a .074 cometic gasket which is probably bringing it down to 8.8-.8.9:1. it's not SO bad n/a once it gets going, but you can definitely feel it struggling down low if you dont rev it out to at least 3500+ in first and second.

Re: high or low comp pistons
 

I'm running 8.5-8.6ish:1 and Now that I'm driving it I realized it was a mistake, Its pretty doggy out of boost have to rev it up to about 4k out of boost to keep up with traffic.

Re: high or low comp pistons
 

yeah but once you start running 30psi you wont care about that anymore.

Re: high or low comp pistons
 

Low comp Cast piston's is the way to go until sumones proves me otherwsie!

Re: high or low comp pistons
 

yup, its about volume of gasses much less than comp ratio.

you dont loose that much torque my dropping compression ratio, and you still poke out the same sized flames to spool it... theres more to it than that, but its not the big deal ppl make of it...

as for the altitude...

you will need more turbo to produce 15psi, but 15psi is still 15psi. and the pistons wont know any different when in boost.

when out of boost, yes, it might be a bit sluggish if you go on the low side, as it will be effectively lower than what they are again...

i'd still go low though. there are plenty of torquey 7:1 motors around...

Re: high or low comp pistons
 

im running 9.0 Cp and lag owns me dont build boost till 35k full boost by 4500-5000