Pumped
"You must increase the fuel pressure 1 pound for each pound of boost," Endress explains. "And fuel pressure must go up as rpm goes up." It's also important to remember that a supercharged car's fuel system sees the same boost levels as its engine-which is why fuel pumps and regulators used in blown applications must be boost referenced. "It means you're referencing either the regulator or the diaphragm in the pump to the level of boost," Endress explains. "If you've got an extra pound of pressure, you put an extra pound of pressure on the diaphragm." In our case, we went with a diaphragm-less fuel pump, choosing one of Race Pumps' piston-style units for blow-through combos, and teamed it with one of its regulators. In our case, 10 pounds of boost meant we needed 10 extra psi of fuel pressure; we started with 4.4 psi in normally aspirated form, then the levels jumped to 14.4 at peak power with our new setup, which was right on the money.
Summing Up
So what did our efforts get us? We had planned on two pulley changes, figuring that a 3.12-inch pulley would put us at around 8 pounds of boost and a 2.95-incher would move us to 9 or 10. In fact, the first pulley change yielded 9.9 pounds of boost at max horsepower, so we stopped there. At this boost level, the 383 in Ganzel's Camaro made an additional 38 rwhp on Vortech's Mustang chassis dyno, along with 30 lb-ft of torque. Figuring in a 15-percent loss factor through this ride's manual trans, we ended up just shy of 500 ponies. It's a good jump in power, and most importantly, it was done without damaging any vital components, which is the best way we can think of to end a dyno session.
Knowing we needed to step up our fuel pressure as we stepped up boost levels, we installed a fuel pump from Race Pumps. According to RP's Howard Stewart, this pump cranks out 150 psi unregulated. "There's normally a pressure drop across the regulator," he tells us. "This has so much more inlet pressure, it's a nonissue. | 
Speaking of regulators, we sourced Race Pumps for this item as well. When boost referenced, fuel pressure increases at a 1:1 ratio with boost. It's also easily adjusted; reading fuel pressure on the dyno (note the sensor), we were able to quickly get our fuel system dialed in. | 
The hardest part of swapping centrifugal blower pulleys is loosening the three belt-tensioner bolts, which isn't really hard at all. Speaking of belts, a pulley change may or not require a shorter belt. Our change, from 3.33 to 3.12 inches, didn't necessitate a belt change; if we'd made it to the 2.95-inch pulley, a shorter belt would have been in order. |