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Thought I'd take a shot at picking the brains of more experienced racers to see if anyone may have some suggestions.

I recently was able to get some dyno time with my car. The engine was breaking up slightly above 5k. I only made two pulls and decided to replace the 30 yr old MSD 6c with a Digital 7. Car ran much better. Set the dyno to 6500 and made a pull. Car broke up badly at 6300 so I lifted and ended my dyno session. Decided it was time to replace the 35yr old Mallory wires and Mopar tach drive distributor. That will be a job for another day. Now to the noise. The car ran and sounded fine when I pulled it off the dyno. Today I fired it to move it out of the garage and there is a deep knock that sounds like it's coming from the rear of the block when the engine is idling. The knock goes away above 1200rpm. There's 90lb of oil pressure, pulled both valve covers and cycled the engine and all the valve train and lifters appear to be working, intact and no broken springs. Did a compression test on all 8 and there are no issues there. Engine spec:
Stock block 446
No fill
Venolia 12.8:1 pistons
BME aluminum rods
stock forged crank
External oiling - single line
SFI flex plate
069j convertor
relatively stock 727

Engine has 200 passes with no issues.
Runs very strong and sounds fine over 1200rpm

The knock sounds terrible, just like real bad detonation. I checked the timing when it's knocking and it's right on 37 degrees.

Any words of wisdom would be greatly appreciated.
Has anyone had a wrist pin clip break and if so what did it sound like? Maybe a cracked flex plate? Broken trans pump (car moves fine though)

Thanks,
Mike
 

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See if the torque converter bolts are loose, or if the flexplate is cracked.
Yep, very common with the BB Mopars. Loose converter bolts can sound like a rod knock.
 

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I had a similar noise that took me years to find. It was a valve tap that would go away above about 1200 rpm. What I found was that on one of the vales the pushrod ball would become disjointed from the rocker socket when the valve closed. After tearing the motor down a half dozen times looking for it I finnaly said the hell with it, I'll run it till it blows. About 1000 passes later I was sitting at my work bench messing with a pushrod and rocker and inadvertaintly, duplicated the noise. I quickly pulled all the pushrods and rockers and grabed a magnifiing glass. Sure enough about half way through the set I found one that had a slaght wear ring around the ball where the rod was tapping on the side of the socket. The problem was caused because the iron heads had been ported and redone a few times without hardened seats installed. One valve ended up being slightly higher in the head which threw off the geometry for the standard length pushrod on that one valve. A slightly longer pushrod solved the problem and it's still running.


But converter bolts are a common problem as already stated. :p
 
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