I have a 383 with 9 1/2 compression, alum heads, moderate cam. Nothing special. 440 HP. It ran great for 2 years. Engine is 5 years old. 3 years ago, the transmission was replaced and after that the pinging started. It was HORRIBLE at anything over 3000 RPM!! I replaced the plugs with the same (Autolite AR3933). It got much better. It started pinging at 4 grand after that. I tried hotter plugs, colder plugs, different brands, different gaps, different wires, etc. It has not been right since. I have changed the plugs, wires, distributor cap, rotor, coil, etc. The AF ratio is great according to a dyno tune. Even the shop couldn't figure out why is was pinging. The timing is only at 11 degrees initial. When new, it was at 14. The timing curve seems correct. All in is only 32 degress or so. I use 93 octane from different stations to be sure it isn't bad gas. It lately has started to "break up" and run like crap at less than 4000 RPM. Is it possible that the MSD distributor is bad or damaged from the tranny swap? It has a Holley 770 Avenger. Is the carb notorious for issues? Was there a wire pinched when the tranny was replaced? I have tried everything I can think of. I am likely going to ship it to an expert soemwhere. I will NOT go back to the builder of the engine because I had a HORRIBLE experience here in VA. I have a video of its terrible performance. I will post a YouTube link soon. Any ideas???

d,
Was there anything really different between the old transmission and the new one that might be causing the problem ? Different converter which might be putting more load on the engine ? Etc.

Does the distributor have a vacuum advance on it ? If not, you should replace it with one that does. I know the discussion has been endless but personally I do not think you can get the proper ignition curve for a STREET DRIVEN engine without having vacuum advance on the distributor. Your total of 32 degrees might be way too much under certain rpm/load conditions. That is where the vacuum advance comes into play. If you got a "tighter" converter with the trans swap, it could be loading the engine down at that rpm.

I would not personally feel real comfortable with someone that has a chassis dyno, and yet cannot figure out why an engine is detonating Where are you in Va ?

Of course nobody ever cracked a cap lowering a engine to change a transmission??

Thanks. I am in Chesapeake/Virginia Beach. The tranny swap and converter were the same. I just had a rebuild. The stall is around 3 grand. As for the timing, it used to run perfectly with 14 initial and 36 total using the same MSD distributor that has a mechanical advance. I thought about changing the springs to heavier ones but the curve seems good and gradual. I have backed off the timing and it still pings.

John, I even changed the dist cap. No luck.

See the video:

I would be tracing down all the vacuum lines from the engine. If they cracked the vacuum modulator or didn't hook it back up, your transmission may still shift OK but now there is a vacuum leak.

Would I have a vacuum line on an HEI MSD that would cause pinging if it is damaged?

cracked cap to check first- is there a rise in coolant temp since trans change if so that will point you in direction of cause

The line would be for vacuum advance. If it were leaking it would just pull in less advance so you'd have less timing at part throttle but no change at wide open when VA drops out. However, it would still be a vacuum leak as far as the engine were concerned.

Thanks. I will check the vacuum lines. That's not going to stop the pinging, is it?

And the cap was changed, Darrell. Everything has been changed. Wish I could figure it out.

Yes, a vacuum leak can cause pinging.

Even with an HEI MSD?? It's a mechanical advance (springs internally).

Could it be from you last load of gas in the tank ?
Try some octane booster.

Thanks. I even tried a full tank of 100 octane. It helped a lot, but it still pings.

You're getting hung up on the distributor part. If a vacuum line going to the distributor is leaking, that's a vacuum leak.

Also, which MSD HEI do you have? If it has a vacuum can on it, remove the vacuum line and plug the port on the carb that the vacuum line is coming from and take it for a spin to see what that does.

I have the MSD 8360. The vacuum port is plugged on it because I use mechanical advance. The carb is hooked up to intake vacuum and the brake power booster.