Constantly pushing the envelope of supercharger design is a combination of several different elements. In 2011, we introduced four new race superchargers, which is unheard of in this industry. In addition to our staff of more than a dozen mechanical engineers and many high-skilled machinists, our in-house manufacturing capability is a big part of what enables us to bring superior products to the market. Five-axis CNC machines, Zeiss coordinate measuring machines, computer modeling software, and engine dynos are just some of the tools that we rely on. Using our CNC equipment, we machine impellers out of 7075-T6 billet aluminum instead of casting them. This allows us to quickly build prototypes without having to spend lots of time and money creating a casting. When produced in bulk, CNC-machining impellers out of billet is more expensive, but it enables us to adapt and modify designs more quickly based on feedback from racers or our own R&D testing. Furthermore, billet impellers are less likely to crack than a casting and are easier to balance. This is very important because an unbalanced impeller will significantly reduce supercharger life. Additionally, ProCharger’s industrial division, Inovair, has benefitted our automotive division greatly. Inovair supplies centrifugal compressors that are used for aircraft deicing for clients such as the U.S. Air Force, FedEx, and UPS. Inovair also supplies centrifugal compressors and blowers for use in pneumatic conveying and other continuous duty applications. Since these machines run 24/7, it gives us a tremendous amount of feedback, which is used to further improve our products.
A centrifugal supercharger and the compressor side of a turbocharger are very similar, but there are pros and cons of each. There are parasitic horsepower losses associated with a supercharger, since it is driven off of the crankshaft. On the other hand, the exhaust side of a turbo transfers heat into the intake charge, which isn’t an issue with a supercharger. Some people think that since turbos are exhaust driven, that it’s free energy, but that’s not entirely accurate. Turbos create backpressure that, when combined with the heat added to the intake charge from the hot side, increases the potential for detonation. Interestingly, if you have two identical motors, but put a turbo on one and a centrifugal supercharger on the other, you might only run 8 psi of boost with the turbo versus 11 psi with blower on 91-octane pump gas. Consequently, blowers will beat turbos on the street on pump gas in net power gain. However, it’s a different story at the track in motors that run on racing fuel or methanol. Since those fuels eliminate the detonation issue with turbos, they make big power. Even so, supercharged cars run more consistently because it’s much easier to manage the boost in them compared to a turbo car. Ultimately, turbo cars qualify well on race day, but supercharged cars win championships.
All superchargers have an optimum operating range in which they are the most efficient. The key issue is understanding what flow and pressure range you are designing the supercharger for. You want to be at the peak island on the compressor map. In industrial applications, you’re targeting a specific pressure and flow range, say 600 cfm at 12 psi, but things are much more complex in a car because pressure and flow are constantly changing with engine rpm. Centrifugals have two key advantages over positive-displacement blowers in this regard. First off, centrifugals produce more power and less heat than any positive-displacement blower. Secondly, centrifugals have a broader operating range. A positive-displacement blower will work well near its peak operating range, but above or below peak operating range, its average efficiency will be much lower. That means there’s less capacity to upgrade the blower by spinning it faster because it has a narrower operating range than a centrifugal blower. Across an engine’s rpm band, a centrifugal supercharger will achieve an average efficiency that’s closer to its peak efficiency. That’s what makes it so easy to pulley a centrifugal blower for more boost as your engine combination grows.