Have you heard the news? Turbos are in vogue. Everyone wants them. They make ridiculous heaps of torque. They have that “free energy” thing going for them, too. With such a glowing list of positive attributes, turbos must be the ultimate power adder, right? Not so fast. Whether it’s in NMCA, NMRA, ADRL, or PSCA competition, supercharged door slammers don’t just give their turbocharged counterparts a run for their money; they often beat them outright. Nothing puts this into perspective better than the impressively long list of national championships won by supercharged cars in high-profile heads-up racing classes over the years. How on earth can superchargers be putting turbos on the trailer? To get some answers on what makes these supercharged freaks run so fast, we went straight to the source and called up Ken Jones of ProCharger. The company’s F-series blowers consistently dominate heads-up drag racing classes, so we were eager to find out why. In addition to dissecting the anatomy of some of the most advanced superchargers on the market, we discussed a host of forced-induction theory, ranging from compressor maps to intercooler design to impeller design to the relationship between pressure and flow. So here’s the scoop.
ProCharger’s F-series superchargers have dominated many heads-up drag racing classes for years, with countless national championships. These blowers feature several design elements that make them outstanding performers. The biggest advantage of these units is our patented friction reduction drive system. That’s where the “F” in the F-series blowers comes from. It’s basically a bearing within a bearing. We’ve experimented with blower designs that very closely control bearing speed, and we found that our allowing the bearings to find their own “happy spot” in a bearing-within-a-bearing arrangement worked just as well. When combined with ProCharger’s self-contained oiling system and transmission, which dramatically improves load carrying capacity, the result is an extremely efficient supercharger assembly. Supercharger impellers can spin in excess of 70,000 rpm, and are therefore very high-speed devices. Naturally, the oiling needs of a supercharger are much different from that of an engine. Blowers need much lighter weight oil for better lubrication of the bearings and gearset. Furthermore, not only does a self-contained oiling system run cooler, it also prevents cross-contamination. These days we’re more concerned with the engine contaminating the supercharger rather than the other way around. There’s always a risk of fire whenever an oil line breaks, but you don’t have to worry about that with a self-contained supercharger.
Superchargers have mechanical and thermal properties that must be taken into account when measuring compressor efficiency. According to Boyle’s Gas Law, there is minimum amount of heat that’s going to be produced anytime air is compressed. Consequently, if a compressor is capable of achieving 100 percent adiabatic efficiency, it would still heat up the intake charge. The reality is that compressors can’t operate at 100 percent efficiency because of the additional heat that’s added to the intake charge due to mechanical components like the gear assembly. Most ProChargers operate at 70-80 percent efficiency, which is similar to a turbocharger. Efficiency matters, but where and how a supercharger is mounted matters too. Positive displacement blowers mount to the top of an engine, and since heat rises, they act as heat sinks. That heat gets transferred into the intake charge. Likewise, mounting a centrifugal supercharger in front of the motor, like in a race car, instead of off to the side nets a cooling effect as well. In the lab, we test superchargers by themselves for efficiency using SAE and industrial test standards, but that only tells you part of the story. To truly measure the efficiency of a supercharger as a system, you have to also look at underhood temps, because that heat will get absorbed into the intake charge and peak air temperature is what you have to tune to in order to prevent detonation.