Has anyone done a compression test on boosted lt1?

[Jose93z28]

Has anyone done a compression test on a boosted lt1? I was wondering what psi I should have per cylinder with 9:5 to 1 compression I would like to know because I know stock should be around 200 psi per cylinder let me knw if any of you guys with lower compression has done one thanks.

[RamAir95TA]

Has anyone done a compression test on a boosted lt1? I was wondering what psi I should have per cylinder with 9:5 to 1 compression I would like to know because I know stock should be around 200 psi per cylinder let me knw if any of you guys with lower compression has done one thanks.

There is no right or wrong answer. Of course a lower compression motor will have less compression than a stock engine. Just as long as your results are within 10% of each other.

[Jose93z28]

Thanks I checked them and 1,3,5 have 125 psi 7 has 120 2, has 110 it's the lowest of all 4,6,8 all have 125 I didn't have leakdown as far as I could tell, I don't knw if these numbers are average or normal for a low compression motor and mine it's a stroker as well, I'm in the process of changing the spark plugs so I decided to check compression while all the plugs were out since I've never done one.

[BIG CAT]

Thanks I checked them and 1,3,5 have 125 psi 7 has 120 2, has 110 it's the lowest of all 4,6,8 all have 125 I didn't have leakdown as far as I could tell, I don't knw if these numbers are average or normal for a low compression motor and mine it's a stroker as well, I'm in the process of changing the spark plugs so I decided to check compression while all the plugs were out since I've never done one.

that sounds a bit low. i would do a leak down test for a more solid answer.

[Jose93z28]

that sounds a bit low. i would do a leak down test for a more solid answer.
Yeah that's why I was wondering if anyone else has check compression psi on a low compression lt1 if I had something similar to compare it to it would give me a better idea of where it should be.

[gregrob]

Arent you up here in Denver? That affects it as well....

As does your cam specs

[zraffz]

Pardon my ignorance for any forced induction motor, but how much pressure will a supercharger force into a cylinder when the motor is only cranking over? I can't imagine it being any significant amount.

[Jose93z28]

Arent you up here in Denver? That affects it as well....

As does your cam specs
Yes I am and I just asked my friend with the white ls1 z28 on spray and he did a compression test on his and he has about 145 per cylinder so I see how you say altitude affects it because I know stock ls1's are suposed to be higher.

[BIG CAT]

Pardon my ignorance for any forced induction motor, but how much pressure will a supercharger force into a cylinder when the motor is only cranking over? I can't imagine it being any significant amount.

No psi will be added. They need a lot more rpm than you will ever see cranking it.

[zraffz]

No psi will be added. They need a lot more rpm than you will ever see cranking it.

Thought so. If it's only making 9.5:1, the motor was obviously taken apart.

Ultimately, the main factor in his cylinder pressure is how his rings were gapped. It'd be hard to say you should make XXX PSI. One guy might make 180 PSI at sea level and you might make 160 PSI at sea level based on how much pressure is bleeding down.


I guess what I am trying to say, is as long as each cylinder is within a few PSI of eachother on your motor, it's probably in good condition.

[BIG CAT]

Thought so. If it's only making 9.5:1, the motor was obviously taken apart.

Ultimately, the main factor in his cylinder pressure is how his rings were gapped. It'd be hard to say you should make XXX PSI. One guy might make 180 PSI at sea level and you might make 160 PSI at sea level based on how much pressure is bleeding down.


I guess what I am trying to say, is as long as each cylinder is within a few PSI of eachother on your motor, it's probably in good condition.

the cam also plays a big role in cranking psi.

[zraffz]

the cam also plays a big role in cranking psi.

Complete forgot to rant about that... but that isn't my spot to preach anyway.