Lately when I'm getting into it I have been getting some pretty severe detonation. My combo is a 9.6to1 440 with FBO set up Mopar perf. dist. and a MSD 6A box with a blaster coil and timing set at 18 deg. initial and 36 deg. total that is all in by 2500 rpm. So today I checked the timing and found that it is fine from the 18 deg. intitial @ 850 rpm and advances fine up to about 1950 rpm, as soon it gets to 2000 rpm and over the timing starts jumping all over the place from about 20 deg. to the 36 deg. total. I am now wondering if my problem is the distributor or the Msd? Any idea's or sugestions?

are you using a dial back light with that MSD.

It is a Snap on digital dial back light but I was not using the dial back feature I was looking at the tape on the damper. I have been using this light for years with no issues before.

A jumping around that severe could not come from the mechanical weight of the dist but would be from the electronics in the MSD or an issue such as a loose connection with the light.

Make sure the intake manifold is sealing. It could be sucking oil and pinging like crazy. Any oil on the valley pan or intake ports?

WHen was the engine rebuilt? Was the oil pump drive replaced? That causes things to bounce around too. detonation is another matter. What cam is in it? What heads?

The heads are ported 516's with 2.14 int. 1.81 exh. valves and the cam is Mopar .474,280 dur. purple shaft. The oil pump drive was replaced about 5 years ago. I will check for oil leaks.
Thanks!!

check the timing light on another car, I had one that I was having problems(timing jumping around) with and found it was the light.