by David Vizard
A carb’s performance is greatly related to booster capability. There is an irony here, however; almost all booster testing is done on a flow bench while all driving is done in a car. When a carb is used for an application that puts it in a high-speed airstream, such as seen on so many drag race cars, the highly turbulent flow over the carb greatly affects the booster’s performance. This turbulent flow leads to what I call “booster buffeting.”
Tests with sensitive electronic pressure measuring gear on a 350-ci 9.5-second drag race car were revealing. As speed built, the booster signal fluctuated at a variable frequency, but on average about 6 to 10 cycles per second with amplitude spikes of as much as 60 percent of the steady-state booster signal were seen on the flow bench.
Also as speed increased, the average booster signal dropped, thus leaning out the mixture to the detriment of the vehicle’s performance. The fix resulted in more speed and is simple: install a large K&N filter.