Z24 compression

[LTM]

I just repaired my 1983 Z24 that has a block\head casting of (10W). Does anyone know what the normal compression is? I looked in the FSM and couldn't find any specs. on compression. I replaced the head with a W04 head and wanted to know how much difference I should expect if any.

[Madkaw]

6 hours ago, LTM said:

I just repaired my 1983 Z24 that has a block\head casting of (10W). Does anyone know what the normal compression is? I looked in the FSM and couldn't find any specs. on compression. I replaced the head with a W04 head and wanted to know how much difference I should expect if any.

150ish

[datzenmike]

The compression ratio is 8.25. But this is the entire swept volume of the cylinder compressed into the cylinder head volume. This would never happen at cranking speeds because the intake valve doesn't close until the piston is 52 degrees past BDC and well up the cylinder. The PSI pressure is not listed but I would expect that brand new it would be 170-180-ish.

 

 A mileage option head would give you about 9.5 compression.

[LTM]

I checked compression on a cold engine and got 140psi in each cylinder. Does that seem to low? This is with the W04 head.

[datzenmike]

Not if it was 120 with the 10W head. It will be a bit higher when warmed up.

 

On a new engine I would expect over 200 PSI with over 9 to one compression. Again it's hard to say. A longer duration cam will show less at cranking speed than a stock cam.

[Stinky]

That is fine.

 

[datzenmike]

It's ok to run low compression if...

 

1/ it's not burning oil (excessively)

2/ the variance between cylinders isn't over 10%

 

It will run smoothly but will lack power and efficiency. It would be called a tired engine.