True or false? Turbochargers are the ultimate power adder. Which side of the fence you sit on is often determined by sheer bias, and there's nothing wrong with that. Like the hot girlfriend that knows she's hot, the outrageous potential of turbo systems comes with a lot of maintenance and a whole lot more money. Superchargers, on the other hand, have always offered a less exotic yet extremely effective alternative. While there was a time when turbos dominated heads-up drag racing classes, the tables are starting to turn. The consistency superchargers offer has resulted in a steady stream of national championships, and in 2013 alone, cars equipped with ProChargers took home five of them. When it comes to pure speed, big centrifugal blowers are now pushing Outlaw 10.5 cars right past the turbo boys, with deep 6-second e.t.'s at more than 230 mph. Feats like this were simply unheard of just a couple of years ago, which reflect how quickly times are changing. To find out how superchargers have become so much more potent in such little time, we interrogated Ken Jones of ProCharger. At the risk of oversimplification, there are a multitude of factors to consider, including compressor efficiency, heat soak, maintenance costs, boost curves, engine load, backpressure, parasitic power loss, inlet air temperature, and timing sensitivity. To get the non-simplified version of how all these factors come together in the great supercharger vs. turbocharger debate, you'll have to keep reading.
Consistent 6-Second Passes
The new crop of supercharged heads-up drag cars running 6-second e.t.'s are giving the turbo cars a run of their money. According to Ken, sheer performance aside, big centrifugal supercharger offer several key advantages over a turbo combo in terms of consistency. "This year, cars running ProChargers won five national championships, which is much harder to accomplish than in years past because there are fewer sanctioning bodies. That consistency has a lot to do with winning championships, and this is where supercharged combinations really shine," Ken opines. Turbo motors require engine load to build boost, and wastegates managed by a boost controller to slowly ramp in the boost off the line to maximize traction. That means the shape of the boost curve can vary from run to run as track conditions change. This requires constant tuning changes through the boost controller, and all these factors can make it difficult to launch consistently in a small-tire drag car. "If a driver has to pedal a car with a turbo motor, the situation becomes even more interesting since the engine might fall off of boost. In contrast, a supercharger has a linear boost curve that's determined by engine rpm and pulley diameter. Having a predictable boost curve makes it much easier to launch a car consistently from pass to pass, and launching consistently is even more important in eighth-mile racing since you don't have the back half of the track to make up for a poor launch. We have a customer named Doug Sikora that runs a 136mm F-3R ProCharger on his 500ci Outlaw 10.5 car. Not only does his car run 6.17 at 230 mph, it runs as consistently as a bracket car. It used to be that turbo cars qualified well and blower cars ran them down in eliminations due to their consistency. Now we run up there with turbo cars in qualifying as well."
Maintenance And Safety
While it's easy to focus on e.t. and trap speed, lowering maintenance also lowers maintenance costs, which greatly improves your chances of showing up at the track in the first place. Ken says that this is another area where supercharged engine combinations really shine. "Running a supercharger is far more cost effective than a twin-turbo setup. With a supercharger, you don't have to build custom headers, and buy a pair of turbos, two wastegates, and a boost controller," he explains. "If you step up to a geardrive, there's virtually zero maintenance required with a supercharger. Since you don't have to load the engine to build boost, a supercharged car doesn't sit on the transbrake nearly as long, so it puts less stress on the transmission. For a driver, pedaling a turbo car can cause the engine to fall off the boost, which isn't an issue with a supercharger. From a safety perspective, with the self-contained oiling system of a supercharger, you don't have to worry about fires from ruptured oil lines during a crash, or puking oil all over the track. Without question, turbos have helped raise the performance bar, but the consistency and lower maintenance of a supercharger are also very appealing."
Greater Efficiency And Boost
Although ProCharged-vehicles have consistently won championships, they seem to have really hit their stride as of late by making some noise in super competitive classes like Outlaw 10.5. "Up to 2,500 hp, superchargers have been competitive with turbochargers for a long time. It's in the 2,500- to 3,100hp range that we've gotten much more competitive in recent years, which is primarily due to the efficiency of our 136mm supercharger," Ken explains. All F-series blowers have a bearing-within-a-bearing design on the output shaft. As the inner bearing finds its friction spot, the outer bearing begins spinning faster. "This improves durability and reduces parasitic load. Unlike a turbocharger, the heat transfer from the exhaust side of the system to the compressor side doesn't compromise a supercharger's efficiency. This heat, combined with the backpressure associated with a turbo, means that turbo motors have a lower detonation threshold. As such, while turbos have a slight power advantage over a supercharger on race gas, supercharged engines make more power on pump gas because they can run more boost before detonation sets in.