compression test results

[Mike 99GSX]

I did a test on my 2g last night. I got 178, 170, 186, 180. I know the target is 178. When they say no more than 14 PSI difference does that mean + or - from 178 or the difference between the highest and lowest cylinder in which I would be out of spec slightly? (170-186 16PSI difference)

 

[HPF_MK3T]

well, when they say no more than 14% difference, they mean between the highest and lowest cylinder. So if 180 is your highest, 154 is the lowest you want to see and they also should list a minimum rating, so if you have a minimum if 140, and your highest is 160, that means 14% would be 137 or so and that would be in the "engine needs work" category.

Thanks,

Joe Schesso
Horsepowerfreaks, Inc
www.horsepowerfreaks.com

 

[Mike 99GSX]

well, when they say no more than 14% difference, they mean between the highest and lowest cylinder.

It says 14 PSI not 14%. Like the post says, my highest is 186 so then I guess my 170 is slightly out of spec. I'm probably worrying about nothing.

 

[TrustGs-R]

Originally posted by Mike 99GSX
I did a test on my 2g last night. I got 178, 170, 186, 180. I know the target is 178. When they say no more than 14 PSI difference does that mean + or - from 178 or the difference between the highest and lowest cylinder in which I would be out of spec slightly? (170-186 16PSI difference)

Your assumption is correct. You look at your highest and lowest cylinder pressures and don't want a variance of >14psi (according to the service manual)....I would say since you have that variance showing in your cyl's.... recheck the highest and lowest cylinders. 186 is pretty high of a compression for stock and 170 isn't normally bad at all.

Hopefully after you recheck the cyl's you'll find something more along the lines of 180 across the board.

 

[Mike 99GSX]

I checked each cylinder 3 times and got the same thing so I think the numbers are accurate. Should I not worry about it?

 

[TrustGs-R]

well..
honestly I wouldn't worry about it if it were my car.

your lowest cyl is still pretty close to where it should be. One cyl is just oddly high.

On all the motors I've ever rebuilt/worked on...My rule of thumb has always been watch for a variance of 10% difference from the highest cyl. (as long as the highest cyl is not too far off from the stock compression you should have). In your case that's 18.6 psi of variance to play with.

In other words with a high cyl of 186...I wouldn't start tripping about it until I had a low cyl of 167.4 (hehe)

 

[HPF_MK3T]

One possible cause for high compression could be carbon deposits in the combustion chamber or on the piston.