ok i have my haynes manual for my ls but now i have an ls/vtec i put in over the weekend thats built for turbo. It has a 81.5mm bore with je 9:1 compression pistons. I havent had a chance to put a guage on it yet and check the comrpession, it pulls really hard and doesnt smoke a bit, but i just wanted to check it to be sure. so what should my compression be for an ls/vtec with a gsr head 81.5mm bore and 9:1 compression?

 

its somewhere around 9.5 :1

 

i know what the actual compression is, its 9:1, what i need to know is when i do a compression test what psi should i get, i think for the ls its around 170 or 180 but im not sure what it should be with this build

 

9.2:1 in a 75mm d-series yields about 190-195psi, id expect 200+ from yours

 

im going by what the haynes manual says, plus i believe the larger the bore is the lower it will be because there is more area for the air to disipate, so i know it would be lower because i have a larger bore and lower compression ratio, im just not sure how much lower

 

you have to remember that tossing a b16 head on a b18a/b block alone will raise compression. i think a stock bottom ls/vtec is rated about 9.7:1

you have slightly lower compression pistons, so hotsex's 9.5:1 is about right. I'm still gonna say 210 ish.

---- it, just go do a compression test. this guesswork BS is gay.

 

well its a gsr head with gsr pistons so its a flat 9:1 compression ratio with a larger bore, im gonna test it when i go back to charleston in a few weeks, that will give me time to run the motor and check it to make sure it doesnt burn oil, it doesnt look or smell to burn oil so far, i just want to test it for namesake

 

And don't worry so much about actual PSI numbers, worry more about variance between the cylinders. Valve timing, acutal compression ratio, stroke, and other variables will change actual pressure numbers. And when you check it, remember to hold the throttle wide open, or your numbers will be lower than actual.

 

yea man, anything over like 180 and within good spec between cylinders is fine.

 

Well if its a GSR head..Its not an LS-Vtec :P And it has GSR pistons...Wouldnt that make it a Stock GSR....Just see what the stock reading should be....