engine busting up

Hey guys been a long time.

Need a little help with some engine trouble.

buddy has a 440 in a 67 Cuda.

the 440 is supposed to be a stock steel crank with ly rods and KB 10.5-1 flat tops. the head are supposed to be Indy Cast with 1.81 and 2.14 valves. the cam is the comp hyd 480 lift not sure of duration or lobe sep. The intake is a torker 2 with a 750 Hollye DP, not sure of the jet and squirter sizes. The Fire comes from a Stock Mopar electronic ingnition. the worst part is the fuel pump and fuel lines. it has a 4 psi elec fuel pump through stock 5/16 fuel lines. The tranny is a TCI Street Fighter with a 2500 stall and 3.55 gears. exhaust are shumacher TRI Ys into 2 1/4 pipes choked down I know.

the problem, car the car fires good and runs hard up to about 3500 then it bust up and when you let off it will back fire. Also going up hill under normal conditions you can hear a I think Mild valve knock. Like maybe it has bad gas. Here is the other thing some time it runs fine all the way up to 6200 and pulls like it should.


hope this is enough info for you guys.

Any help would be Great. He just bought the car and is trying to get it to pull right.


Thanks Chad