prelittlelude

Ok so i was running some thoughts through my head, and I am not sure if this has been covered but maybe someone can shed some light. I’ve been thinking a lot about what compression ratio to run when i build my motor.

OK i know not all my numbers might be right or the calculations but bare with me you will get the idea
So say I did 8.5:1 and ran 11 psi of boost,

11 + 14.5(atmospheric pressure roughly) * 8.5 = cylinder pressure of 216.75

Now if i up the compression ratio to say 10 and try to get the same cylinder pressure

216.75( cylinder pressure) / 10 = 21.675 - 14.5 = 7.175 psi

so what my calculations say is that at 8.5:1 at 11 psi i get a cylinder pressure of 216.75 and if i up my compression ratio to 10 and try to reach the same cylinder pressure i would only have to run 7.2 psi

SO i guess what my question: Just because the calculations say that i will have equal cylinder pressure by adjusting the boost after i change the compression ratio, does this mean i will make more or less or the same power?


EDIT: i know some of my cylinder pressure numbers might be off because im not sure how to take in to account for the dome of the head, but you get the idea of my question

prelittlelude

up,, come on neone have any input?

symba

knowledge is limited but I will tell you this...At 8.5 you will run like $hit off boost which if this is a daily driver-will suck..at 10:1 you will still have good off boost power and loads of torque. Tuning will be more so of an issue at 10:1. not much room for error. But there is someone running an h23 at 10.2:1 and making somehwere around 250-300 hp and like 2225-250 ft-lbs of torque. I'll try and find some info.

ok, his member name is DLB1994 and here are some figures
94 accord built h23 dynoed 337whp 313wtq at only 12psi

I have asked him myself and he has no problems with detonation. he's got great tuning. there are others who run in the upper 9 to over 10 compression but this one was at the top of my head. there are some good threads in the archives regarding high and low compression with turbo

prelittlelude

thanks for the info, but i think my underlying question is , that if i have equivalent cylinder pressure but use different compression ratios and boost numbers to reach that cylinder pressure what does that do to horsepower, ie high compression low boost, or high boost low compression. to me it seems that i should make almost the same amount of power but it should shift the power curve and peak onset.