heads compression

[steve berry]

my Bridgeport is at 120 per hole if I take 20 thou off the heads I should be at what compression I don't wont to go over 145 or 150 thanks guys steve

[TODD_TN]

Steve,

I'm about to do the same thing to a 2.5 I'm building. A well known engine builder here in the south
tells me it will take about .050 - .060 to get around 140-145 psi. ** BUT ** He did stress to sneak
up on it.

I'm gonna take about .020 at a time til I get an average between 140 and 145 psi.

Hope this helps.

[90 5.0]

I want to say 32cc's on the 2.4 is the correct size for 145-50. No idea how much that is but should be less than a 2.5 needs cut due to smaller combustion chambers??

[bobthebuilder]

Try a set of 2.0 heads on the BP. They are 34cc from factory..

[Schramer]

Have no clue what is needed on 2.4ltr heads but it is APPROXIMATELY 13 thousandths deck per cc on say, a set of 260 heads......doubt this will help but I try as best I can lol!

[Keaten]

Just put a set of 2.0 heads (34cc) with 1.2 mm head gaskets on my BP, it was 120 psi ...now its 135psi per hole...hope this info helps

[bobthebuilder]

Keaten , your running compression will be 145 to 150 if cranking speed comp is 135.. the compression running is what it really is where cranking sort of tells condition or health of the cyls.. I cut many sets of heads here in my shop and I can measure the CC's while it is still on the mill. I sometimes just cut some to 35cc but some folks want the max for pump gas which is about 32cc. The older 2 piece hemi chamber heads for a 2.0L is plenty for a 2.4L engine and that way you have stock heads to go back to if you ever want to. The 2 piece heads seemed to run slightly better than the newer one piece ones..

[Keaten]

Ok thanks, i will also add that i tryed a 1.6 mm head gasket from serria and the cranking compression was 125 psi.. Can someone explain how to do a running compression test.

[W2F a V-King]

Unless it's different than a 4 stroke...you literally remove the spark plug on one cylinder, screw in the compression gauge, start the motor and read the running compression. Ground the plug wire removed while doing this. I don't go over idle speed. Hit the purge a few times to get a good average.

That's about it..repeat in each hole as needed! :thumbsup:

I have not tried it on my outboards, but will next time I run one on the hose...jus fer grins...:D

James