Kevin Williamson
Mobile, AL
Answer: Bog is a vague term that may mean different things to different people. Here, I interpret what you call bog to mean the engine flattens out and doesn’t want to rev or pull at rpm in gear. Yes, your combo would run better with a Performer RPM intake and 3.55 or 3.70 gears, but the existing hardware should not be causing the car to flatten out at 4,000-5,000 rpm. Almost certainly, you have a fuel-delivery or tuning problem. A marginal fuel-delivery system can be crutched in the lower gears because low gears provide a torque multiplication assist. In the higher gears, the engine must accelerate the weight of the car on its own, which can put a marginal fuel-supply system over the edge.
So check out that fuel pump. Plumb in a pressure gauge and monitor the fuel pressure. Anything below 3.5 psi on the top end is unacceptable-it indicates the pump or fuel-supply system is not keeping up with the engine’s fuel requirements or the fuel filter is clogged or restrictive. A high-flow inline fuel filter is preferred over the restrictive sintered-iron fuel-bowl inlet filters. The fuel line should be at least 3/8 inch or larger; try to keep bends to a minimum.
If fuel pressure is OK, check the pump output volume. A high-perf fuel pump should fill up a 1-gallon bucket in well under a minute. Finally, check the pump’s vacuum draw. As read on a vacuum gauge T’d into the fuel line back by the tank sending unit, there should be no less than 13 inches of vacuum. Low vacuum here means the sock, strainer, or screen inside the fuel tank is clogged or has collapsed.