compression

[Dragkid1917]

im going to do a compression test because theres definitly sumthing rong with the valves or a piston or sumthing but anyway i need to know what Psi my compression should be at.

[fastTa]

If you suspect something is wrong with the valvetrain or the rings, a leakdown test would prove to show a better diagnosis. You don't want any higher than a 10% leakdown on a stock motor.

If you will be just doing a static compression test, a healthy LT1 can range anywhere between 170 PSI and 215 PSI. The thing to look for in doing a static compression test is not so much the peak numbers, but the variance amongst all 8 cylinders.

Don't forget to pull the PCM BAT fuse to disable fuel and spark, and keep the TB blade wide open. It's also a good idea to perform any kind of compression check with the motor fully warmed up, but with the LT1's tight quarters it is very hard.

[Dragkid1917]

what about an ls1.... same deal? and another thing thats weird is when i put my car on the stand today i put it in neutral ans it still kept the tires spinning slowley. Why does it do that? And while im on wheels... can u put 17X9 front and 18X9 rear or will it mess stuff up.

[Crazy Canuk]

Here is a good link on the subject.

http://www.newcovenant.com/speedcraf...ompression.htm

I was wondering about this myself. I had mine done when I had a missfire and a bad vibration he told me that there was only a 5psi varrience between all 8 cylinders and said it was realy good, I was like wow that is good, not knowing what he was talking about

About the diffrence in rims, no not a problem as long as your ride hight dosn't change. If you have 18" rims on the back you need a smaller side wall with the tires. Also make sure your rim offsets are right or your going to run into fit problems. Do a search on this subject a ton of info on rims and tire sizes here to read up on

[fastTa]

what about an ls1.... same deal? and another thing thats weird is when i put my car on the stand today i put it in neutral ans it still kept the tires spinning slowley. Why does it do that? And while im on wheels... can u put 17X9 front and 18X9 rear or will it mess stuff up.

I've gotten bad about just assuming every one here has an LT1.

Everything I said still applies with the exception of the expected cylinder pressure readings. LS1's typically range between 165-195 PSI.

One more thing I forgot to add....it is agreed by most that the 4th compression stroke will yield the most realistic cylinder pressure reading. Crank the motor and you will see the needle on the gauge pulse on each compression stroke.

[Dragkid1917]

ok will do. Do you know about why the tire might still turn when its in neutral thoo, ?.. im trying to do this all at once befor i put it back on the road so ill prolly have a bunch of questions

[fastTa]

ok will do. Do you know about why the tire might still turn when its in neutral thoo, ?.. im trying to do this all at once befor i put it back on the road so ill prolly have a bunch of questions.

That's completely normal. There is still a bit of bleed-by pressure being applied to the overrun clutch in neutral.

You can use 17" up front and 18" in the back. Just make sure the overall tire diameter on the 18" wheel is as close to 25.66" as possible as not to throw off your speedo calibration.