i have been searching for the correct psi for a compression check, but i cant find any deffinitive answers. i am running a gsr head, and itr pistons on an ls bottom end and i was wondering if any one could help me with the right psi to look for.

 

in all actuality, all gauges are different. no two will sho the same #'s even if ther is a set amount of psi per compression ratio. i did two different compression test on my motor. one was 195 195 193 195. the other compression tester i used said 225, 225 220 and 225.


its not so much the amount of the numbers, but more so if one is lower by a large amount above the stock specs. or if a set is lower, for instance, 195 195 70 70 either your h/g is leaking between those two cylinders, or your rings are shot or ring lands busted.


if a number is low and its because rings, you take a spray bottle and put some 30w oil in it and spray it in he cylinder thats low, if it comes up quite a bit its your rings.

 

thanks for the info but i was wondering if there is supposed to be an actual psi. because if i check it and it reads the same across all for (lets say 190) then i still dont know if i have lost compression in all four cylinders. from my searches i have found it to be about 230-235 and i was just wondering if some one knew this for a fact. especially since i have higher compression.

 

how many times did you let the engine turn over on each test? My ls vtec has 9.1 compression ratio dish pistons and it reads 180-182 psi all the way across the board on 5 strokes. I would think that the @11.1 compression ratio that you're hitting should be closer to @220

as far as the dude stated before if you add oil to the cylinders and it greatly improves the compression test you rings may be shot. Depending on how long they have been in there is there any chance that they may not have been broken in properly?

 

im not sure, the guy who built my motor let his buddy drag it after the build, but i still drove 500 to try and break it in.

 

use the oil technique and get back to us. The rings may have not seated and it may need to be pulled apart and re-honed

 

thanks, i was more worried about piston slap, than loss of comp. but i was hopping that if i was lossing comp. then it was just the rings instead of a bad hone job. my motor has only about 6000 mi on the fresh rebuild.

 

if there was piston slap you would probably hear it.

 

remember that the results will differ greatly everywhere because of height above sea level, temperature, humidity. everyones are different, your looking for steady numbers that are withen like 5 or so % of eachother.

 

alright thanks for the info, im gonna try it tonight, hopefully everything isnt too bad.

 

finally checked compression, #1 peak=180 hold=175 #2 peak=180 hold =175 #3 p=155 h=150 #4 p=180 h=175. so obviously my rings are probly bad in the #3 cylinder.

did test with eng. at norm operating temp with 5 cranks each time and did each cylinder 3 times. motor only has bout 6000 miles on fresh rebuild with new pistons and rings. is this too early for bad rings or is it a sign of a bad hone job??

 

and just incase you guys think these numbers are low this is my build

98 gsr head port & polish
ctr cams
98 itr valves w/3angle
jdm itr .25 over pistons
ls rods
ls balnaced crank
b18b block

should these numbers be this low??

 

That's way too low. Do you have the gas pedal pressed down when you do the compression test? The throttle body has to be open to get a good reading. My LsVtec with b16 head and p30os pistons has almost 240 all across.

 

no i didnt have the gas down at all. does it effect the numbers that much tho??