just installed 383 stroker with blower. car starts but backfires at idle. we checked all wires and plugs. checkes valves and compression. the only thing that we can think of now is my ECU. i had it tuned last year for the stock bottom end and blower. so now the compression on the 383 is 8.5:1 instead of 10.5:1 so could that be the problem.
everything else on the motor is the same as what it was tuned for, injectors, cam etc..

 

yeah it's most likely your compression. Is there any chance it's something with tuning?