You’ve got questions, we’ve got answers. We work with the Summit Racing tech department to help you tackle your auto-related conundrums. In this week’s Mailbag, we’re troubleshooting a backfiring problem on a 427 big block Chevy.


Q: I have a 1974 Olds Omega with a 427 cubic-inch big block Chevy. The engine has an Erson cam (292-degree duration, .514-inch lift), an Edelbrock Performer intake, a Carter 750 cfm carburetor, MSD 6A ignition and Blaster 2 coil, Holley electric fuel pump set at 7 psi, headers, and a Flowmaster exhaust.

At about 4,000 rpm, the engine backfires through the carburetor. I have been told the compression (11:1) is too high. I tried some VP “red” race fuel, and that seemed to help. I tried adjusting the timing and the carburetor, but that made things worse. I even pulled the timing chain to make sure it was okay. I have tried everything I know to try, and I still have the backfire. Any suggestions?

(Image/Jim Smart)

A: Are you running the valve springs recommended for that Erson camshaft? If not, we think the valve springs you have aren’t suited for the cam, and should be replaced with the manufacturer-recommended springs. Also, we suggest you continue to run the VP race gas. With 11:1 compression, you’re going to need it all of the time to prevent detonation.