Best Blower For Your Mustang - Choose Your Weapon - Tech

Now that we've extolled the virtues of the boost/power formula, we can tell you why motors usually don't reach the stated power outputs. The first problem is that the formula doesn't take into account parasitic losses associated with driving the supercharger. In the case of a high-horsepower application, the supercharger may consume 50-100 hp or more, and this power is subtracted directly from the output of the supercharged combination. If the boost pressure of 10 psi was to supply a mass flow gain able to support a 0.68 percent increase, you would still have to subtract the parasitic losses associated with driving the blower. Due to the increase in heat associated with the increase in compression (to 10 psi), the number of oxygen molecules per volume is less than it would be at atmospheric pressure. Therefore, the increase in pressure of 0.68 percent (to 10 psi) will not likely yield a commensurate gain in power, though intercooling can improve the air density (number of molecules per volume). Despite these seemingly insurmountable odds, we often reach the power suggested by the power/boost formula on both 5.0 and mod motors alike by combining a healthy and powerful normally aspirated combination with an efficient supercharger.

While it's hard to beat the turbos for maximum power per pound of boost, superchargers offer a number of things not available from turbo kits, namely ease of installation and emissions certification. The problem with most turbo kits (the rear-mounted STS systems are obviously the exception) is that they require removal or repositioning of the catalytic converters. This is obviously a big no-no when dealing with emissions certification. By contrast, supercharger kits don't require alterations of the exhaust system, though additional power is usually available by upgrading the headers and after-cat exhaust. Since the superchargers bolt to the top of the motor, they have little or no effect on the emissions output, assuming the tune is spot on. We're still waiting for emissions-legal turbo kits, but the market is chock full of blower kits for the 5.0 and mod-motor families. The fact that no exhaust modifications are necessary for a supercharger kit also means that installing a supercharger is usually easier than a comparable turbo kit.

Type Cast
When it comes to blower kits, there are basically three different designs from which to choose-the ever-popular Roots-style blower, its distant cousin the twin-screw, and the one that started this whole boost craze, the centrifugal.

All three have their strengths and weaknesses, including the much-maligned factory Roots-style blowers. Companies such as Whipple and Kenne Bell have made a business out of replacing the less-efficient Roots-style blower, but the design does have its strengths. Being a positive-displacement supercharger, the Roots-style blower offers immediate boost response. There's nothing better than sticking your foot into the throttle of a Lightning, Cobra, or GT500, and watching the boost gauge flicker with excitement. Roots-style blowers are employed as OEM equipment on Fords because they offer an exceptional combination of cost, performance, and durability. Obviously, the design must meet the performance and longevity specifications for the application, but so too must these design goals be met at the lowest-possible price point. If the power goal of your performance motor is just 390 hp, why install a more expensive blower capable of 500, 600, or even 700 hp? For all but the most powerful factory force-fed Fords, the Roots-style blower makes an excellent choice.