New engine issues

PRH said

If that info is correct, it’s only 9:1 if the heads are 73 cc’s.

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Yes, I agree with the numbers.... Here is one that looks pretty much 'at the top', but is actually down .016". So without measurements, or a piston PN and any info on the block being decked, we don't really know.



I can' think of any 318 flat top piston that has a near zero deck height without valve reliefs; all the one with no reliefs are stock replacement types at stock CH. Perhaps the OP is just repeating the old Mopar advertising spec when the 9:1 is related??

The 120 psi cranking pressure says low SCR and/or late intake closing. The stock 318 readings would be closer to 130 psi.

PRH said

My feeling is........ with cams that have extremely slow closing ramps, some compression starts to build before the valve is actually “seated”.
The valve is closing, the piston is ascending....... and if the piston is displacing more area than can squeeze through the small opening the almost seated valve has provided, some pressure will start to build.
So, if you tested two cams with the same exact actual closing points, but had radically different closing ramps(one really slow vs one that just slams the valve down), they would show different readings on the compression tester.
Although the calculation would say the cranking pressure would be the same.

It’s the same reason that a 292* cam could have 20* of vacuum.
The number of overlap degrees might be large, but the area under the overlap curve is still rather small because the valves aren’t open very far.

This 292/292-112 cam has the same overlap as the MP 484 cam, which is 284/284-108. Both have 68*.

Think that 484 cam would idle at 20” in this 318?

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Yes I agree with that thinking; I tend to adjust the numbers of advertised duration down a bit with some cams in an attempt to compensate for this. Not sure my 'adjustments' are exactly right LOL but it is in recognition of this factor. Yet, no, I would not expect the MP484 to idle at 20".....

These specs in the Erson catalog are the TQ20H cam.

(Edit to add: All questions answered above before reading the prior 2 posts.)