What is a good comp reading? - Team Camaro Tech
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post #1 of 4 (permalink) Old Jun 25th, 03, 05:31 AM Thread Starter
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For a stock 307 CID V8? I have 120-130 psi on all eight cylinders, wet w/oil squirted into the cylinders. 1974 Motors Manual reads 9:1 comp ratio.

I suspect a retarded cam, not necessarily from the institution...........LOL. Timing chain slack is 1/8 inch at the pointer.

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post #2 of 4 (permalink) Old Jun 25th, 03, 06:16 PM
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That's not too bad. Were the throttle blades held open during the test? I would have expected you to get more like 140 - 160 with a stock cam so sounds like the motor may have some wear. The important thing is that the cylinders are within 10% of each other - which they are according to your values.

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post #3 of 4 (permalink) Old Jun 26th, 03, 01:13 AM Thread Starter
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Thanks for the reply, dnult. Yes, the throttle plates were open during testing. I did the mark the harmonic balancer 30* BTDC using the pointer and a pencil. I removed the drvr valve cover and checked the intake valve opening point. Books read 26*, 28*, and 29* BTDC. I got 0* before the pushrod started to move. With this info, and low vacuum, I suspect late valve timing.

I believe the above problem is related to three dead cylinders during idle to 3K rpm and low(?) vacuum, i.e., 17-18". Apply more throttle, above 3K, and those 3 cylinders come into play. Another carb did not help. Good spark is available. Engine has been rebuilt before my time, how well, I don't know. It doesn't smoke or burn oil, plugs are clean.

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post #4 of 4 (permalink) Old Jun 26th, 03, 11:22 AM
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Sounds like the chain may have slipped or something doesn't it. Keep in mind that the opening figures are in cam degrees, so 30* at the cam is 60* on the crank. Perhaps you've already accounted for this - I don't know the spec.

-dnult

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