compression test results seem high?

[sdstang]

So I did a little research on my piston and heads and something is very much a miss. My heads are D1AE-CB so they should be 74-77cc.

With these pistons I should be at 9to1, no where near 12to1.

How much do you need to shave off these heads to get down to say 50cc.

 

[[email protected]]

Just to put your mind at rest, our original 71 M code had 190-195# all around. Quench heads, had been rebuilt with use of supposedly 9.5 flat top pistons. Sold engine to a friend to put in his 70 cougar. He broke the engine down machine shop checked it out , 10 10 crank 30 over bores still with cross hatch. heads redone with hardened seats. In short nothing wrong, ran great and checked out great. Compression test was run at sea level +/- (Sacramento CA)

Relax and enjoy !!!

 

[Danand]

The camshaft is likely advanced too far. If the cam is stock, or is of near stock duration, having it installed advanced a few degrees will get you numbers up where you're at. I would expect that your initial ignition timing would have to be retarded quite a bit to keep your engine out of detonation at lower RPMs?

 

[sdstang]

The camshaft is likely advanced too far. If the cam is stock, or is of near stock duration, having it installed advanced a few degrees will get you numbers up where you're at. I would expect that your initial ignition timing would have to be retarded quite a bit to keep your engine out of detonation at lower RPMs?

Should I try to correct this? I have the engine out of the car and will be taking off the timing cover to change the gasket. The have 8k on the motor the way it is.

Jim

 

[Jeff73Mach1]

Not unless you are going to pull the heads as well. The issue I would be worried about in changing cam timing is valve to piston clearance. If you change cam timing on an unknown cam in an engine that you didn't build, how will you verify piston to valve clearance? You have to pull the heads!

You originally posted the engine ran well with no problems-leave it alone.

 

[mach71351c]

When I drove the car I felt that it ran very well. Don't touch it.

 

[sdstang]

Ok I'll leave it as it is.