340 build advice needed

moper said

Compression depends on which cam. Make sure you degree the MP cam. I would prefer it to be under 10:1 and run a milder camshaft but that's me. I ran a similar 9.?:1 340 with the '71 intake and carb, a Comp HE268 cam, and headers. Was a GREAT street package in an E body. Would be even better in a car with more gear and 500lbs less.

Click to expand...

I got curious...... With the 268 cam and an SCR of 9.7, your engine's DCR would have been at or a hair above the same DCR at the OP's with a 284 cam.... assuming the OP's purple cam is truly a 284 duration at around .005"... and assuming 9.? = 9.7 LOL.

The OP can easily drop 0.20 to 0.3 points off of both SCR and DCR just by putting the standard Felpro 8553PT head gaskets. That'll add some margin against detonation.

And good a well cooled engine and engine compartment is going to be a part of the picture, either way.

For total perspective, I DID have quench in the 10.3 engine (which the OP will not have) and was cautious (and limited) on ignition timing. The cam was 254 intake duration and a 114 LSA (for fuel mileage) and was installed with around a 60-62* ABDC intake closing so DCR was up there in the 8.3 range. It was run from sea level to 6k feet. But, in 7-8 years and 95k miles, I only got one bad batch of gas, and never touched the ignition timing once I got it set (stock point distributor). And this engine was used with a stock converter and I even towed with it.... both of which will tend to promote the occurrence of detonation.

The high stall converter and high rear gear that the OP has will help him to stay away from detonation regardless of his CR.