compression

[jamienlogan]

what is ideal psi compression for a 440 11:1
last I checked I only had 100

[GPracer2500]

It depends on: the accuracy of the static compression spec, the elevation, the gaskets used, the cam used (which I see is a HC stg 2), and other things.

However, with excellent cylinder sealing (rings and valves), at 1000ft elevation, and assuming the 11:1 spec is accurate, you should see maybe 175 to 190 psi. I'm making certain assumptions to get to those figures but it should be pretty close.

At 100psi I'd expect the engine to barely run. If your guage is only reading 100psi then make sure the guage is accurate and you're performing the test correctly.

[underpowered]

^^^^^Yupp. at 100PSI it would be very hard to start, may even have to be push started. around 100 is about the limit to run on most engines.

also, what exact procedure did you use to check compression? it should be done on a warm motor, holding the throttle wide open and cranking untill the gauge stops climbing.

[scruff_mcruff]

Originally posted by underpowered
^^^^^Yupp. at 100PSI it would be very hard to start, may even have to be push started. around 100 is about the limit to run on most engines.



my engine ran fine with 70psi of compression w the stock low comp piston. honda says the service limit is 90 psi. after i did the 11:1 piston and after break in i had 145 psi w/ the stock cam.

[GPracer2500]

The auto decompression mechanism used on the stock cam skews the numbers downward. The auto decomp keeps one of the exhaust valves open a little at cranking speed so you don't get a true measure of dynamic comp.