Q: I have a Trans Am powered by a 406 small block Chevy. The engine has 9.67:1 compression, GM cast iron cylinder heads with Crane roller rockers, an Edelbrock Performer cam (214 degrees duration at .050, .442 inches of lift), a Holley 600 cfm carburetor on an Edelbrock Performer RPM intake, and Hooker Competition headers. The ignition is a GM HEI with Mr. Gasket advance springs and weights installed.
The engine runs strong (even with 2.73 gears), but has a slight hesitation at all rpms. The carburetor was completely cleaned and has a Holley Trick Kit. I changed the squirters and accelerator pump cams, but that did not help. What is causing my car to hesitate? Is the problem with the distributor advance or perhaps fuel pressure? I’m thinking about replacing the distributor with a Summit blueprinted HEI distributor, and replacing the stock fuel pump with a Holley mechanical pump. Would these changes help cure the hesitation?R.H.
A: Your hesitation is likely related to the mechanical advance setting in the distributor and a lean condition due to the restriction posed by the relatively small cfm carburetor. The Summit distributor is a good idea, and you should also consider upgrading the carburetor to a Holley 750 cfm vacuum secondary.
We’d recommend that you stick with the stock fuel pump because it is compatible with the stock fuel tank venting system. If the pump is bad, use an ACDelco replacement pump and add a fuel pressure regulator to monitor pressure to the carburetor. Finally, we’d suggest changing the rear axle gear ratio to a 3.42 or 3.73 to help with torque multiplication.