Increasing Cylinder compression

[Anonymous]

Is there a way to increase cylinder compression? After I rebuild my engine, I performed several cylinder compression tests on the motor. What I noticed disturbed me a bit. Before the rebuild the average of the five (no.2 was 30 PSI) was 150 PSI or so. Now, after the rebuild I'm not getting anything above 130 PSI.

Before the rebuild it had the original steel head gasket and stock pistons. Now, .020" over pistons (small dish) and FelPro head gasket.

The engine runs very smooth (as long as it gets fuel, another problem) but should I really worry about the difference in cylinder compression? If I remove the cylinder head and shave .045" from it this should increase the compression, right? Does it matter?


-Chris

 

[Asa]

has it been broken in yet?
if not, wait till it has been, then do it again and see what it is

 

[Mustangaroo]

Chris,
Your compression is down because of the thicker head gasket you installed, the new head gaskets are about .025 thicker than the steel one you had on the engine before your rebuild. Most of us either deck the block or mill the head to keep the commpression up to 9:2 - 9:5 per original Ford spec's. You can still get the old metal head gaskets, someone posted a source a few weeks back, do a search and you should find it or maybe someone (MarkP?) will post the location.

 

[Anonymous]

Thanks!


-Chris

 

[ASMART]

Remeber that pressure will rise after the break in due to the rings will be sealing better. Also, another factor is the bore increase. That SHOULD actually provide a slight increase in compresion ratio because the bore size contributes much more cylinder volume than it does to combustion chamber volume. Ihave not done the calculations so take what I said about the comp ratio with a grain of salt.

Anson

 

[mugsy]

Personally that 30 PSI cylinder would worry me, big time!! Did you test for what was leaking? I mean that is way too low!! Either the valve(s) are shot or the rings are pretty much gone or there is a big ol' hole in yer piston! I would re-test and verify that reading. To be able to tell if it the rings or not, after the first re-test, squirt some motor oil thru the spark plug hole into the cylinder. And re-test again, if the pressure rises then the rings are the leakers. If the pressure remains the same then the valve(s) are not sealing, or your piston is perforated.

tanx,
Mugsy

 

[Anonymous]

I think I miss lead you guys. The 30 PSI was before the rebuild (hence a rebuilt was necessary). I'll wait and recheck the cylinder compression after I drive the car for a few weeks - let it break in.


-Chris