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.
Parasitic Load Vs. Backpressure
Although hot rodders are well aware of the parasitic power loss that comes with driving a supercharger off the crankshaft, the detriments of the exhaust backpressure created by a turbo system are often overlooked. Although it's difficult to put exact figures on how much power loss is associated with both a supercharger's parasitic load and a turbocharger's backpressure, the numbers could be much closer than most people think. "The theory that turbos give you free horsepower is ridiculous. Turbos don't have parasitic loss, but the exhaust backpressure they have to deal with means that superchargers make more power on pump gas," he says. "In race gas applications, superchargers and turbos run similar e.t.'s at similar boost levels, so the power loss from parasitic load and backpressure may be similar. Plumbing a turbo in the exhaust system is like putting a banana in your tailpipe. Any exhaust that isn't scavenged out of the cylinders adds heat to the combustion chambers, which lowers the detonation threshold and lowers how much boost you can safely run on pump gas. In a high-compression late-model engine like an LS3 small-block, a supercharger can run 15 to 20 percent more boost, and that more than offsets any parasitic power loss."
Air naturally heats up as it is compressed, and the more efficient the compressor, the less heat it adds to the compressed air charge. According to Ken, although standardized tests can effectively measure compressor efficiency in a lab, there are a multitude of factors that lab testing can't simulate. "We think that SAE J1723, a testing standard intended to measure compressor efficiency, is highly problematic. It only measures the efficiency of the supercharger itself, and does not account for the effects of engine compartment heat transfer, intercooling, oil temperature, and supercharger mounting location," Ken explains. "Most people don't just buy a supercharger, they buy a supercharger system. By mounting a centrifugal superchager off to the side of the engine, you effectively isolate it from engine heat. Since heat rises and positive-displacement superchargers are mounted on top of the engine, they are very susceptible to heat soak. Also, limited hood clearance often results in an undersized intercooler, and any ornamental engine shrouding a manufacturer bolts on top of the engine traps in even more heat. In the case of a turbocharger, exhaust gas temperature can exceed 1,600 degrees. That heat transfers over to the compressor side of the turbo and decreases efficiency. Likewise, a self-contained oiling system runs much cooler than a turbo running off engine oil, resulting in less heat transfer into the compressor. Pump gas is the real litmus test for compressor efficiency, and centrifugal superchargers are proven to make the most horsepower on pump gas."
Minimizing inlet air temperature is imperative to maximizing power and durability in any forced induction application. Although intercooling is arguably the most effective method of lowering IAT, the plumbing on the induction side of the compressor is very important as well. "To properly engineer a supercharger system, you have to monitor IAT from the air filter, to the compressor outlet, to the intercooler, to the discharge piping, and to the throttle -body throughout a quarter-mile run. If you have restrictions in flow path anywhere between the air filter and air inlet on the supercharger, it increases parasitic power consumption," Ken explains. "In the case of a turbo, it will actually increase backpressure. If locating the air filter away from heat requires making a long inlet tube with tons of bends, you're better off bolting a rear-facing filter directly on the blower. Heat off the headers will rise into the filter at idle, which is obviously very bad, but last I checked you're not racing at idle. As a car moves down track, by the time it reaches 20 mph IAT will be within 3 to 5 degrees of ambient temperature. Sure you can pulley the blower down to overcome the restriction on the inlet side, but all that does is increase parasitic power loss and generate more heat. If you try to hot lap a forced induction motor at the track, the shortcomings of the induction system become very obvious. With a properly designed intercooler, recovery time from heat in the induction system is very quick."
Although traditional belt-drive systems can work great in supercharged applications up to 2,000 hp, as engine output quickly eclipsed that mark, racers demanded an improved means of spinning up their superchargers. The aftermarket responded with gear drive systems that allow driving a supercharger directly off the crank through a series of gears instead of a belt. "At extremely high power levels, gear drives are more reliable. Having a backfire at the track can throw off a belt, but that's not an issue with a gear drive," says Ken. Likewise, gear drives eliminate side loads off of the crank snout, and reduce parasitic power loss as well. Mounting the supercharger directly in front of the engine also allows fabricating a ram air system that feeds cool ambient air into the supercharger inlet. Through necessity, ProCharger has developed its own gear drive system called the RaceDrive. "While developing the F-4 supercharger, we overshot our power goals and developed a supercharger unit capable of 3,500 hp. This exceeded the limitations of the gear case, which led to the development of the RaceDrive. The gears in the RaceDrive are very easy to swap out if you want to change the blower speed, and it had additional drives for a fuel pump or a vacuum pump. It also offers great ground clearance for superchargers with large volutes."
Low-End Torque And Top-End Power
Despite the all-out power and efficiency that centrifugal superchargers offer, the long-standing knock against them is that they don't build boost until high rpm. Since centrifugal superchargers rely on fixed internal step-up ratios and engine rpm to determine boost, it has long been accepted that it's impossible for centrifugals to produce lots of boost at low rpm, but ProCharger has transcended the impossible with its ingenious new i-1 supercharger unit. "The i-1 supercharger utilizes a continuously variable transmission coupled to a standard gear case. The CVT multiplies the supercharger's internal 8:1 step-up ratio by as much as 2:1 at low rpm, and as little as .5:1 at high rpm," Ken explains. "The result is an incredibly flat boost curve that offers the high-rpm horsepower that centrifugal superchargers are known for as well as immediate boost at low rpm. The CVT employs a remarkably durable dry hybrid drive system, and the CVT's ratio is controlled by a sophisticated electric motor. With the i-1 supercharger, now you don't have to worry about the shape of the boost curve anymore, which allows us to design the supercharger for peak efficiency. On a 2010 Camaro SS, the i-1 supercharger system produces 425 lb-ft of rear-wheel torque at just 2,400 rpm on a Mustang chassis dyno. The peak figures check in at 568 hp and 538 lb-ft of torque at the rear wheels on just 7.5 psi of boost. The shape of boost curve isn't as important on a race car, but in street applications it's very important to maximize the area under the curve."
Granted that integrating a CVT into a supercharger is earth shattering in its own right; that only tells half the story of the i-1. Since the CVT ratio is controlled by an electric motor, hot rodders can also dial in the exact amount of boost they want at the touch of a button. The i-1 supercharger system includes an in-car touchscreen that can load programs for three boost modes into the i-1's electronic brain: Touring (low boost), Sport (medium boost), and Competition (high boost). "Touring mode locks the supercharger at 1 psi, so it gives you peace of mind when you hand the keys over to your wife, or if you have to drive in bad weather. Changing between modes also changes the amount of blower whine, so it's fun to surprise people at stop lights," says Ken. "The i-1 also has a Custom mode that allows users to program a custom boost curve in 250-rpm increments. You can also change the rate of boost gain, and dial in throttle response by customizing the amount of boost that's produced at part throttle. You can even have custom boost curves for drag racing and road racing. In addition to performance and customizability, we have some customers that are reporting a 2- to 3-mpg improvement in gas mileage on the freeway."
Some people think that all intercoolers are created equal, and these days, there are lots of cheap knock-off intercoolers on eBay. As the saying goes, you often get what you pay for, and high-quality intercoolers offer several advantages that an untrained eye might not notice. "First and foremost, ProCharger is proud to design and manufacture all of our products in America, including our intercoolers. The performance of an intercooler comes down to its design, testing, and manufacturing quality," Ken explains. "You can't easily see what's going on inside an intercooler, but the use of turbulators inside the cores, the ratio of crossflow air to charge air, and the location and design of the end tanks all play a very important role in intercooler performance. The leak rate of cheap intercoolers is fairly high, and many users will never know how severely they're leaking. Furthermore, parts like intercoolers can't be designed in a vacuum. They have to be designed within the context of how they're going to fit in a car. In some of our supercharger kits, upgrading from one of our Stage 2 intercoolers to one of our race level intercoolers can increase quarter-mile trap speed by four mph. Improvements like that aren't simply the product of increasing the core size. The entire intercooler system must be refined from top to bottom.