excessive engine ping
Thread Starter
Cruising
Joined: Sep 2005
Posts: 11
Likes: 0
excessive engine ping
Any help appreciated, I have a 77, automatic trans. powered by a 383 stroker, the heads are gm performance fast burns, gm performance vortec intake with a street demon 650 carb-the car is extremely fast but when under load or take off it pings severely.i have backed the initial timing down to 6-8 degrees adv. (which is lower than the 14-16 demon recommends) with no improvement.i have tried octane booster,even cam 2.. I run the gm perf.distributor (hei) could the advance springs be too light and coming on too soon.what do you think guys?????
Le Mans Master
Joined: Jul 1999
Posts: 9,206
Likes: 17
From: Sewell NJ
The 383 from GM with Vortec type heads specifies no more than 29 degrees total mechanical advance. If you are using a distributor set at the traditional 32 - 36 degrees you have to recurve it.
Race Director
Joined: Mar 2001
Posts: 11,322
Likes: 1
From: Living in the Hartland
Do you have your vac adv hooked up? If so remove and drive it, if the pinging stops then it is your vac adv (need to limit it) if it does not stop then you need to back your timing off some, as the others have said the vortec comb chamber heads like a little less timing then old sytle heads but you need to recurve the dist to get max performance, will be weak off idle if you just back the timing off without recurving it
Burning Brakes
Joined: Aug 2002
Posts: 1,146
Likes: 10
From: Scottsboro Alabama
Originally Posted by Fevre
Do you have your vac adv hooked up? If so remove and drive it, if the pinging stops then it is your vac adv (need to limit it) if it does not stop then you need to back your timing off some, as the others have said the vortec comb chamber heads like a little less timing then old sytle heads but you need to recurve the dist to get max performance, will be weak off idle if you just back the timing off without recurving it
Recurve it and try a different vacuum advance can.
Le Mans Master
Joined: Jul 2005
Posts: 5,752
Likes: 4
From: Austin Texas
The G.M. "Fast-Burn" heads sport 62 cc.chambers. You better have a serious dish on those pistons....On my 383 with flat-tops (-5cc valve reliefs) and 70 cc chambers, I am right at 11:1 with .029 head gasket. 
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Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
Sound like your dynamic compression might be to high too. Octane boosters don't do a whole lot to the actual octane rating. Distributor recurve and if that don't work worst case you might have to change the cam to reduce dynamic compression. There are some posts on here about economically boosting the octane with some hardware store solvents but I haven't tried them yet. Preignition and detonation will kill your new motor. A cam change is a lot cheaper than rebuilding it again
