Richard Holdener
June 1, 2008
Photos By: Greg Jarem

Though it may be difficult to believe, superchargers actually predated the fuel-injected 5.0 Mustang. To us at MM&FF, it wasn't until 1986-when Ford replaced the carburetor with a long-runner fuel-injection manifold-that 5.0 Mustang supercharging came of age. Modern 4.6 enthusiasts have the 5.0 to thank for the current crop of superchargers available for modular motors.

Those of us with a few years under our belts remember when the Paxton planetary-drive blowers were the only game in town, and actually running across one on the street was a real surprise. Those early planetary-drive Paxton blowers have since given way to such impressive offerings as the gear-driven Novi 1000, 1200, and (my favorite) the ever-impressive Novi 2000. Where early Paxton blowers were hard pressed to support 500 hp, the modern Novi 2000 is capable of more than doubling that number. Paxton now offers self-lubricated models of these impressive blowers. Though the innovators of Mustang supercharger kits, Paxton isn't alone in supercharger offerings for the Blue Oval brigade.

Paxton is one of the oldest names in supercharging for Mustangs. The California-based company offered kits for older Stangs as well as for EFI 5.0 Mustangs dating back to the late '80s.

Today, kits are also available from the likes of ATI ProCharger, Ford Racing Performance Parts, Kenne Bell, Magnuson, Powerdyne, Saleen, Roush, Vortech, and Whipple, to name a few. And how could we not to mention the various supercharger offerings directly from Ford?

While Ford did offer (Paxton) supercharged motors back when Carroll Shelby was putting the hurt on Ferrari, the modern era likely began with the M62 supercharger applied to the Ford Thunderbird Super Coupe. The 3.8 V-6 was equipped not only with modern fuel injection, but also a positive-displacement Roots-style supercharger and intercooler to provide the 3.8 V-6 with 5.0 V-8-like performance. Ford supplied truck owners with an impressive gift in the form of the 5.4 Lightning truck. An easy 14-second machine right off the showroom floor (13s if driven well), the Lightning mill demonstrated that the Two-Valve mod motors really responded to boost, and what motor doesn't?

Internally, centrifugal blowers feature a transmission that steps up the ratio of engine speed to impeller speed.

Ford added an M112 Roots-style supercharger to the 4.6 DOHC engines in '03-'04 Cobras, then applied an even more impressive 2.3 twin-screw blower to the all-aluminum 5.4 mod motor used in the GT. Ford fol-lowed up with the Eaton-powered 5.4 Shelby GT500 motor.

To date, the all-aluminum Ford GT isn't only the most powerful mod motor ever offered, but quite possibly the most impressive one Ford has ever offered in a production car. Rated at 550 hp, the supercharged 5.4 has been tested to produce near that 550hp power rating at the wheels. I'd pit this supercharged mod motor against a stock 427 side oiler, 428 Cobra Jet, or Boss 429 any day.

Magnuson's MagnaCharger has a Roots-style kit available for S197 Mustangs. The kit (which you can read about on page 158) offers a smart and good-looking design, not to mention serious power potential.

Though the 5.0 can be credited for introducing the modern performance world to supercharging, the 4.6 has not only continued, but also expanded, the popularity of forced induction. At last count, there were approximately 10 different supercharger manufacturers offering kits directly for the modular Ford family.

That there are so many manufacturers involved should give you an idea about the popularity of the supercharged mod motors. In the end, it's the enthusiast who benefits from the proliferation of available kits, as competition improves the product line and decreases the eventual cost to the consumer. Having 10 different manufacturers also provides variety. This is an important fact, as contrary to the propaganda you read on some Web sites, there's no one ideal form of supercharging for either the original 5.0 or the mod-motor family.

Were there one form that excelled above all others and provided the very best of every comparison variable, no other form would continue to exist. Fortunately for us enthusiasts, this is simply not the case, as variety allows you to pick and choose the best combination to meet your particular needs. Centrifugal superchargers perform a certain way, as do Roots-style and twin-screw blowers.

Centrifugal blowerS, such as this unit from ProCharger, mount to the front of the engine and are driven by the crank.

So, Which Is The Best?
That depends on where you place your emphasis. Before purchasing a blower, you should ask yourself some important questions. Are you looking for maximum (peak) power production from your suitably built 5.0 or 4.6 Two-Valve motor? If so, you will probably be best served by the centrifugal design. If instantaneous boost response is more important, then you should lean toward either of the positive-displacement designs (Roots-style or twin-screw). There are obviously positive and negative attributes to each type of supercharger, but in the end the choice will likely come down to a great many more variables than just peak power.

You'll need to consider cost, kit completeness, ease of installation, availability, customer service, and-most importantly-tuning. Does the supercharger kit come with an ECU program designed to provide maximum safe performance on pump gas? Does the kit include the necessary injector upgrade, fuel-pump upgrade, or ignition amplifier? Once installed, how difficult is it to further increase the power output? Is it more involved than a simple pulley change (it almost always is)? We've only scratched the surface here in terms of considerations when choosing a supercharger for your Mustang or fast Ford, but know that all of them will offer a significant power gain.

Ford Racing Performance Parts recently released this new TVS blower for the GT500. It's capable of 700-plus horsepower.

Just be sure that the tune (air/fuel and especially timing) are spot on before putting your foot into the throttle. All too often owners bolt on the new power adder and shortly thereafter blow the engine, only to blame the part. Few ever recognize or admit the real problem was a poor tune and the owner's inability to realize it.

The great thing about supercharging is that it provides significant power gains regardless of the original motor. It doesn't matter whether you have a stock 5.0L or a wild 4.6L Cobra motor, adding a supercharger can increase the power output by 40-50 percent. Obviously, larger gains are possible, but make sure the motor is able to withstand the additional stress. Ford (or any manufacturer) doesn't often design blocks, connecting rods, and pistons to withstand double the original power output.

Whether the blower kit is a simple M90 from FRPP or an intercooled YS-Trim from Vortech, adding one to your Ford motor will yield impressive dividends. One convenient way to calculate the power potential offered by any supercharger is to take the power output of the normally aspirated motor and multiply it by the boost pressure as a function of atmospheric pressure. Since a normally aspirated motor runs at an atmospheric pressure of 14.7 psi (or 1 BAR), all you have to do to double the power output of the motor (in theory) is to double the pressure to the motor. Meaning that if your normally aspirated mod motor produced 300 hp, all you have to do to reach 600 hp is to double the pressure or supply 14.7 psi of boost using a supercharger. If you supply only 7.35 psi, you should see a corresponding power gain of roughly 50 percent since 7.35 psi is 50 percent of 14.7 psi. The simple math formula is as follows: Supercharged HP = NA HP x Boost Pressure/14.7 +1.

Today's blowers fit under the hood and are driven by either a serpentine pulley like this one or with a cog pulley for racing and serious street applications.

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.

Swapping a smaller pulley in place of a larger one spins the blower faster, thus making greater boost. This often results in additional horsepower, until the point is reached where the blower loses efficiency due to excessive heat being generated.

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.

There are many sizes and types of intercoolers on the market. Some are front mounted, while others are integrated into the intake manifold.

If you've already purchased an '03-'04 Cobra, Lighting, GT500, or Ford GT, and don't want to replace the supercharger you already own, it's possible to both increase the boost pressure and overall power potential of your factory blower with porting. Proper porting of the stock blower can unleash some additional power, just don't expect it to surpass the efficiency of a good twin-screw, as the Roots-style blower (including the new TVS from Eaton) is still down on power compared to a similar-sized twin-screw.

Speaking of twin-screw superchargers, the impressive design offers all the boost response of the Roots-style blower with significantly improved efficiency. This increased efficiency includes a reduction in the parasitic losses associated with spinning the blower, as well as a decrease in the charge temperature at any given boost level. Compared at the same boost level, the twin-screw design will produce more power than the Roots-style blower. This performance differential escalates as we increase the boost pressure, as Roots-style blowers become less efficient at elevated boost levels. By comparison, twin-screw blowers can be run effectively at boost pressures exceeding 20 psi. Naturally, either blower will run best with some form of intercooling at these elevated boost levels.

The centrifugal supercharger is the design that started the supercharger craze in the early days of the 5.0 Mustangs. I remember lusting after a Paxton (or McCulloch) blower back when Ford first introduced the fuelie Mustang. After running the Silver State Open Road race in my normally aspirated 5.0 LX, I was convinced that a 5.0 Mustang could win the event overall if it was equipped with a supercharger. This eventually came to pass when I managed to take the overall win in my Vortech-powered LX at an average speed of 167 mph. Of course, it didn't hurt that some of the heavy-hitting Unlimited class cars fell by the wayside with mechanical troubles, but to finish first, you must first finish. This form of racing proves that the reliability of a centrifugal supercharger is first-rate, even when run at full throttle for 32 minutes straight. From a basic standpoint, the centrifugal supercharger can be thought of as a mechanically driven turbocharger. The reduced impeller speed relative to a turbo requires a slightly different impeller design, but know that centrifugal superchargers are currently available to feed motors up to 2,000-plus horsepower. Regardless of how much power you want to make, centrifugal supercharger manufacturers have you covered.

If you're looking for serious horsepower, you should consider upgrading other parts of the vehicle, such as the engine internals and the fuel system. Later, you may also want to install a stronger-than-stock transmission and aftermarket axles.

If you take a look at the power production offered by a good blower setup, just about any system will provide plenty of additional power over the normally aspirated combination. Blower systems are currently available to support in excess of 2,000 hp, so even the wildest combination is no problem. While big numbers impress on the forums and help sell magazines, the reality is that most of us run blower motors that produce substantially less power.

For some, a stock motor with a blower is more than enough. Even if you add ported heads, cam, and an intake, you're still talking about a streetable package that won't prohibit you from driving your supercharged combination on a daily basis. With plenty of power available from most any combination, other factors must be considered when choosing the proverbial "best blower" for your application.

The first issue is cost. Owners of factory force-fed Fords already have a supercharged motor, so there's no need to purchase anything. Just add boost with a smaller blower pulley, some tuning, and maybe an after-cat exhaust, and you're on your way. Of course, the factory-supercharged motors can all benefit from a blower upgrade. From an installation and cost standpoint, upgrading a motor already equipped with a blower is probably the easiest way to go.

Whipple has been busy selling its new 3.4 twin-screw blower for Lightnings and Shelby GT500s.

For guys looking to get boost on a budget, centrifugal supercharger kits are available for less than $2,000, though these typically lack all of the components required for a complete installation. Know that adding a supercharger to an otherwise-stock 5.0 or 4.6 motor may require fuel-system upgrades (injector and/or fuel pump), programming changes, or at the very least, a rising-rate fuel-pressure regulator. Make sure when ordering that all of the components required for the installation are included with the kit. Stay away from those electric supercharger kits promising extra horsepower for just $69.95. There's no way an electric fan will provide enough airflow or pressure to support the needs of a decent 5.0 or 4.6. A crank-driven supercharger can easily require 50 hp to produce the desired power gains. Do you have any idea how big a 50hp electric motor is or just what the power requirement would be to spin it? As a rule of thumb, if the gadget seems too good to be true, it usually is. You can realistically expect to drop a couple grand on a decent blower setup-more if you start adding options to the list.

Though we have concentrated on the fuelie Fords, there are plenty of supercharger kits available for carbureted motors as well. Both Roots-style and centrifugal supercharger kits exist that provide plenty of power. Just make sure to get the proper carburetor for the boost application. ATI, Paxton, Vortech, and Weiand all offer kits for the carbureted crowd and can help you select the proper carburetor for your application.

Keeping Cool
No discussion of modern street supercharging would be complete without covering the topic of intercooling. The unfortunate side effect of supercharging any motor is that the elevated inlet air pressure we see as boost generates unwanted heat. It's a simple fact of nature that compression causes heat. More boost equals higher inlet charge temperatures. Elevated inlet charge temps are bad because they increase the likelihood of harmful detonation. To combat the increase in charge temperature, blower companies resort to intercooling, which is nothing more than a heat exchanger used to remove some of the unwanted heat from the inlet air.

Intercoolers work by exposing the heated charge air to a cooling medium. In air-to-air intercoolers, the cooling medium is ambient air. The increased surface area of the air-to-air intercooler (relative to the discharge tube) helps radiate the heat from the charge air out to the ambient air. This is caused by the temperature differential between the heated charge air and the cooler ambient air, combined with the heat dissipation properties of aluminum. Often, this type of intercooler is placed in the airflow, so overall flow increases with vehicle speed. On air-to-water intercoolers, the surface area of the intercooler can be reduced dramatically thanks to the use of a denser and therefore much more efficient transfer medium-water.

Whenever talk turns to intercooling, there's inevitably a fight between the air-to-air proponents and those on the side of air-to-water. Let's clear things up right away and say that just like with supercharging, there's no absolute best form of intercooling. For maximum heat rejection, running ice water or some other super-cool transfer medium in an air-to-water is the ultimate setup. This system is often employed in drag racing and even at the Bonneville Salt Flats, where the run time is short as not to use up all the ice. The downside is that you'd have to constantly refill the ice in the system to keep it at optimum cooling capacity. Air-to-water systems can obviously be run using just water (though never with the same water used to cool the motor), but such a system usually requires a second heat exchanger to rid the system of the heat put in by the elevated charge temps. Such a system is employed by Ford on factory Lightning, Cobra, and GT500 motors. These systems work well for the limited full-throttle runs seen on the street or even at the strip, though many enthusiasts opt for ice water at the strip.

Roush also offers this new blower, which is similar to the TVS from FRPP. This is likely to be the unit found on the soon-to-be-released P-51 Roush Mustang.

Air-to-water intercoolers work well for short periods or when there's ample cooling time between uses, but what about sustained use? For something like the Silver State open road race where the motor is subjected to full throttle boost for as long as 30 minutes at a time, an air-to-air intercooler would be best suited. The reason for this is that the elevated speeds run in the open road race provide plenty of cooling for a front-mounted intercooler. In essence, the high speed provides all of the cooling air to maximize the efficiency of the intercooler. Such a system will still not match the efficiency of an air-to-water run with ice water, but how much ice water would you need to run flat out for 30 minutes? The answer is that you could never carry enough, so the air-to-air intercooler is the setup for lengthy high-speed events.

You should now be asking, which system is best for street use? The answer is actually that both systems work excellent on the street. In fact, despite the claims by the various manufacturers, you'd be hard pressed to determine the difference between a good air-to-air and air-to-water system running street boost levels. Both forms are used successfully by OEMs as well as the various aftermarket blower manufacturers. As is the case with blowers, choosing the best form of intercooling is more a matter of cost and complexity than overall efficiency.

Supercharger Shootout-Roots vs. Twin Screw vs. Centrifugal (11 psi)
The power curve supplied was generated by running a Roots-style blower, a twin-screw, and a centrifugal supercharger on the same motor at the same maximum boost level. The timing and air/fuel curves were also kept constant for each application. Putting these numbers into proper perspective is the fact that this 4.6 DOHC motor produced 426 hp in normally aspirated trim before installing any of the blowers. It's clear that the two positive-displacement superchargers (Roots-style and twin-screw) offered much more power in the lower rev ranges than the centrifugal.

The centrifugal offered the greatest peak power of the bunch when tested on the 4.6 Four-Valve motor, but is peak power all you're after?

Since most of your driving takes place in the lower rev ranges, the positive-displacement superchargers have plenty to offer. Even the factory Roots-style blower on the '03 Cobra motor offered plenty of average power, it just was unable to keep pace with the more efficient twin-screw design. The great thing about the twin-screw is that it makes for one heck of a blower upgrade to almost any factory force-fed Ford. Replace the Roots-style blower with a twin-screw on your Lightning, Cobra, or GT500, and you're looking at some serious power potential. Regardless of which one you choose for your application, supercharging your Stang will result in some serious power.