Compression Check Insanity
Thread Starter
Teching In
Joined: Mar 2006
Posts: 7
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Compression Check Insanity Thought I would throw a compression check on my 408 for some "after break-in" (2500mi) baseline numbers before I move to spray....
Here's what I got. All done with motor warm, all plugs pulled, 4 cycles, throttle open, fuel off.
1 - 232
2 - 218
3 - 220
4 - 206
5 - 210
6 - 210
7 - 230
8 - 209
Static is 11.34:1
So after I did this I rechecked 4 and 6 with a little oil... only 1-2 psi change. The motor runs awesome, only used maybe 1qt oil since day one (through 2 changes) doesn't smoke at all, etc.... Just the variance in #s got me puzzled. Hrmmmm..... Should this really even concern me much?
-JH
Here's what I got. All done with motor warm, all plugs pulled, 4 cycles, throttle open, fuel off.
1 - 232
2 - 218
3 - 220
4 - 206
5 - 210
6 - 210
7 - 230
8 - 209
Static is 11.34:1
So after I did this I rechecked 4 and 6 with a little oil... only 1-2 psi change. The motor runs awesome, only used maybe 1qt oil since day one (through 2 changes) doesn't smoke at all, etc.... Just the variance in #s got me puzzled. Hrmmmm..... Should this really even concern me much?
-JH
The spec. will vary from engine to engine...Some manufacturers say no more than 25% variance between cylinders..other manufacturers say no more than 10 PSI variance between all the cylinders. If it was my car, the next step i would do is a leakdown test, if it passes the leakdown with no problem..i would not worry about it anymore. If there is a problem, you should be able to pin-point where its leaking from with the leakdown test.
Thread Starter
Teching In
Joined: Mar 2006
Posts: 7
Likes: 0
Alright finally got to a leakdown.....
All 8 cyl. were between 4-7% warm and the higher leakdown numbers of the cyls didn't correlate to the lower compression psi cyls much.
So what would cause the diff. in compression psi?
BTW... doing a leakdown test is a bitch with a hot car and 11:1 compression. hehe....
So I am going to assume this motor is GTG with the spray....
All 8 cyl. were between 4-7% warm and the higher leakdown numbers of the cyls didn't correlate to the lower compression psi cyls much.
So what would cause the diff. in compression psi?
BTW... doing a leakdown test is a bitch with a hot car and 11:1 compression. hehe....
So I am going to assume this motor is GTG with the spray....
