I just did a compression test on my 383 and its only at about 130-135 on all cylinders. This doesnt seeem right at all with my compression ratio. Maybe my starter is not fast enough? What rpm should I be cranking the engine over to get an accurate reading? I figured my engine should have atleast 180 pounds or so.
Well, thats what I thought. I figured mine should be atleast 180, so 130 doesnt seem right at all. I can only think of a few things that are causing this.
1) The gauge is bad (though unlikely its a new MAC)
2) I installed my cam off by a tooth or two and retarded the cam timing
3) My timing chain is toast and the stretch has retarded the cam timing a bunch. How much would it have to be off to make a 60 psi difference in cranking pressure?
I will be checking again with the carb wide open and a different gauge asap.
The timing chain would have to be pretty far off. When I installed my cam, I wanted to see how the cranking compression changes as I advance and retard the cam. What I found was that moving the cam 4* either way changed the compression by 10-15PSI. Not a whole lot.
If that were the case, you'd have to be off by 20* or so.
Lead Mechanical Engineer
Art Morrison Ent. Inc.
I finally did another compression test with a brand new gauge, I also changed my method. I wired the carb to full throttle, pulled the plugs and hooked up a battery charger. It spun much better than last time and I got 198-200psi on all cylinders, that sounds better than 130. I was amazed there wasnt more than 2psi difference between all cylinders, which is great.