[PONTIAC DUDE]

Originally Posted by mechanic17

P-Dude, I should have said the engine WAS pinging at idle as long as the computer had control of the timing (TBI systems will do that to raise an "unacceptable" idle). Now that I'm on a carb and non-comp HEI, it pings only when it is revved up in park (no load). And, under accelerating load, of course.

The cam is installed correctly--this was rechecked. However, I did not degree this one (in other words, either the chain, cam itself, or a tolerance stack could be contributing to an error.) Another, I suppose, argument for "non-tuners" to go easy on SCR. Engine tolerance for low octane fuel will vary because of these sorts of "built-in" problems. Naturally, the proper degree procedure would have picked up this problem, if it indeed exists.

My personal, current theory is that 9.5 SCR is combining with overefficient valve timing at lower rpms (3k and below) to create too much cylinder pressure. IF that turns out to be the case, (and assuming the factory claim of 9.5 is accurate for this engine) then 9.5 may not be a "safe" number after all, or at least not an "idiot-proof" one. And if it isn't, then we need to work out one that is for people who will insist on being conservative because they don't like to experiment with their cars, time, parts, and money.

Had to do the over 100 post. LOL.

I also subscribe more to the ............ if over 185 cranking compression you might be more susceptible to knocking conditions. But not a general rule either.