Hey guys, my zz383 is timed at 12 deg btdc @ approx. 1000 rpms and 32 deg btdc @ approx. 3000 rpms. However, when I drive the car at normal operating temp of 180 deg, I hear the dreaded marble sound (faintly) that sounds like overheating. My fans are constantly running by design and I have a high flow thermostat set for 170 deg. I have read conflicting reports of where timing should be at ( 29 - 36 deg ). Can anyone offer some ideas.

Try bringing the base timing back to 8 or 10 degrees and i it should go away. Leave the btdc for now but u may have to retard that 2* but try adjusting your base timing. Is this carb or FI? 180 is a really good temp for a 383, at 220 i would start to get worried. I personally run a 165 thermostat.

Are you running a vacuum advance? If so, how much advance is it adding? Is the pinging at light, part, or WOT? I am running a ZZ4 based
engine with the LT4 hotcam. Right now I have it at 15 degrees & 36 total all in by 3200 Runs great on 93 fuel. If your cam has a lot of overlap, you can usually get away with a little more advance. What distributer are you running?

sorry about the delay in answering back but I was out of town. the dist is a proform hei and has vacuum advance of 20 degrees. My rpm gauge is out of wack so it's hard to get base rpm. Also my temp sending unit is screwed into intake manifold, is that an accurate location to get temp from ? The pinging is at cruising speed and if I go wot I don't hear it.

forgot to mention, I am running a carb setup with a mallory 4309. Anyone know the ideal psi to run, mine is at about 4 psi.

Lowered timing to 10 deg base and problem doesn't seem as severe. Don't get why GMPP says to set timing to 32 deg @ 3000 on this crate engine ? Am I missing something obvious ?

I think 20 degrees advance on avcuum might be too much for your setup. Under WOT the vacuum advance doesn't have any effect, so that might explain your symptoms. AS you probably allready know, the vacuum advance is just to give the engine better street manners & improve miliage under light loads. If most of your timing is coming in early, plus 20 degrees vacuum, that sure might be a formula for detonation under light load & light throttle. I would set the timing back to the higher settings, then leave your vac advance disconnected, & drive it around. If you have no pinging at that point, I would consider getting an adjustible vac advance.

Doesn't hurt to try. I'll post the results when I do it.