We have a Mopar B block 400. We had a reputable engine builder build a 400 hp powerpant. Milled, balanced. Pistons .024 below deck. 906 heads milled and cc'd at 82, Competition Cam XE262H.Intake 218, Exhaust 224 at .050, ;lift .462 and .470, hydraulic lifters. We have a 383 forged crank, headers. 650 Holley. Put this in a 1970 roadrunner automatic. It performs like dad's 383 2 bbl family sedan. When you wing the throttle, it backfires once in intake. Here's the real puzzler. The backfire disappears and runs best with no pinging at 50 degrees initial advance timing. You have to go to 70 degrees initial timing before there is any resistance during cranking. Can anyone suggest what the problem is before we pull the engine.

 

I would start by checking the dampner timing marks Slipped ? Wrong timing cover ? Did they use the 383 dampner ? for the 383 crank ???

 

Don't guess, get a piston stop and find true TDC then time it with a light.

And Welcome

 

It has the correct dampner, and timing cover. We did find true top dead center and timed it with a timing light. We have tried everything we could think of. We also took the valve covers off and made sure everything was kosher. Everything looks right, but we are missing something.

 

Either the cam is in wrong, the timing marks are wrong, or the advance in the distributor is effed up. All this is easy to check

Timing marks.........use a piston stop. You say you checked. HOW?

Cam..........you don't need to tear it down to get an "idea" of whether it's right or wrong. Get the cam timing card, "rig" an indicator on the no 1 valve, and put a degree wheel on the balancer. You can do all this in the car, pull the belts and probably the fan. If you don't know how, Google "how to degree a cam" Probably the easiest is to use the intake lobe, as the intake opens not long BTC, so this is easy to "see" even without a degree wheel.

Distributor.........Does it have a locked advance, stuck, rusted? Some racers USE a locked distributor and simply time it for max power advance, but it should NOT be up around 50!!!!!

Last, might be a "wrench" like a stuck or bent valve. Run compression check and leakdown check.

 

My guess is you're referencing the wrong plug wire with your timing light. #1 cyl is all the way in the front, driver's side.

 

This reminds me............There has been troubles with MSD ignitions and "dial back" (delay) timing lights, so for what that is worth..................