A small-block Chevy oil pump...
A small-block Chevy oil pump is in fact a Roots-style pump. The medium being moved enters at the top. From there, it is carried around the outside of the case between the gear teeth. As the gear teeth remesh on the lower side, the medium being pumped is squeezed out from between the gears and discharges out the lower side of the case. The mechanism is very basic in function, but is not very efficient in this form.
For a mechanically driven turbine supercharger (ProCharger, Vortech, Paxton) of the type originally pioneered by Paxton 60 years ago, we find the situation a little different. Because the drive ratio between the supercharger and the engine is fixed (Paxton did actually develop a variable drive unit used on Ford Thunderbirds back in the late 1950s), limiting top end boost while trying to enhance low-speed boost comes down mostly to impeller design and overall unit sizing. In that area, significant strides have been made just in the last 15 years.
Bolt-On Power: Making A ChoiceThe heyday for blowers of any type starts now, and goes into the near foreseeable future. As for those of you concerned that the push for fuel economy may spell the end of big power, fear not. There are plenty of ways to employ a supercharger to both enhance performance and improve mileage-and that means they are not going away anytime soon. If you are in the market for additional power in the form of a bolt-on, then your only problem is making a decision as to which system you should use.
Draw-through or blow-through...
Draw-through or blow-through carb?The advantage of stepping up and spending three grand on an injection setup is that there is zero fiddling and zero doubt about the tune when you are done. Getting the fuel curve right on is just a matter of reading the O2 sensor output and adjusting it accordingly-that's if the injection system itself didn't actually do it for you. Going the carbureted route can save between $1,000 and $2,000, but you will almost certainly need to do at least a little fine-tuning. If the blower is a Roots-style unit, then the most obvious and convenient place to put carburetion is on top of the blower. This is the classic draw-through mode of operation. Apart from referencing the power valve to the intake manifold boost, the carb pretty much operates normally. But with some installations, building a draw-through system is not quite as easy. Centrifugal superchargers sort of fall into this category. Here, it is more convenient to have a blow-through system. Unless you have a carb built by a company knowledgeable in this mode of operation, be aware that on a scale of zero to 10, your carb calibration problems could easily be five or more, when what you need are zero problems. As for what you may give away in terms of power, the chances are the small deficit might actually help hook up the potentially large number of lb-ft the engine will inevitably make if done right.
When Low-Speed Torque Sets The RulesIf you have a truck (like me) that you want performance from, but it really has to function as a truck and do useful work, then a positive-displacement unit is almost certainly the way to go. My 2000 4.8 GMC Sierra has to haul a payload as much as 10,000 pounds when taking the race car to the track. To do this effectively, it needed real low-speed grunt, along with the capability to deliver good mileage. Up to this point, I had experience with the Holley/Weiand kits, Magnuson, Edelbrock, and Whipple, but mostly with the Holley/Weiand and Magnuson stuff. A few years ago, on a mild-cammed 350 with pocket-ported aluminum heads, I saw some 541 hp and 545 lb-ft using a Holley/Weiand blower. That's a pretty good showing for what is essentially one of the lower-cost installations on the market. But since the truck was to be used for long-haul towing, mileage was very much on my mind, and I had not, up to this point, tested a Magnuson setup with the bypass valve. This valve, also used on the Edelbrock blowers, reduces parasitic losses to barely above what it takes to spin a couple of sets of roller bearings. So with mileage in mind, I selected a bypass-valve-equipped positive-displacement kit, in this instance from Magnuson. Because the Magnuson kit was charge cooled via a water-to-air intercooler between the blower and block, it could manage 8 psi on a 9:1 engine without being detonation-prone or octane-sensitive. To make the most of the blower, the stock 4.8 heads were ported, and a Gale Banks exhaust system installed. Dyno tuning was done at Custom Performance, and PCMforless burned a custom program for us. Results were very satisfying. Quarter-mile performance showed up just short, by a truck's length, when run against a stock '04 Mustang GT. Freeway mileage just missed the 21-mpg mark by a hair's breadth, while a consistent 17 mpg was seen about town. That was virtually unchanged from stock. When towing, mileage was surprisingly good. I saw low 14s. Maybe the trick for performance and mileage is a smaller engine with an efficient blower. Since I tested this unit from Magnuson, they have made yet another significant step forward in rotor design. In fact, as we go to press, rotor design seems to be a hot topic and some new developments from Edelbrock are in the works. Some insider info indicates we should stay tuned on this one.
At this point, we can say that for off-idle and low-speed torque, a positive-displacement blower is the ticket. But what if you are happy with the output of your engine up to about the 2,000-2,500-rpm mark? If that's the case, then a whole slew of supercharger types become a viable bolt-on option, and that's what we'll look at now.
Centrifugal SuperchargerFor the most part, the easiest installation is a belt-driven centrifugal blower, rather than a turbo. Although they may lack the low-speed capability of a positive-displacement blower, they can usually deliver a cooler boosted charge, thus allowing more power to be developed before an intercooler or water injection becomes necessary. That said, most installations still take advantage of boost cooling by an intercooler. As a result, a 10-psi ProCharger unit feeding an otherwise stock 4.6-liter, Three-Valve '07 Mustang shows some impressive bolt-on gains. A ProCharger kit, as per the Mustang shown on p. 64, was able to boost rear-wheel horsepower from typically 260 to just over 460.
This 540-inch street-cammed...
This 540-inch street-cammed big-block Chevy is essentially a simple build. As-cast Dart 325 heads, an 8.7:1 compression ratio, and a Barry Grant blow-through 850 Demon carb make up the essentials. When this was used with a basic non-intercooled F-1R ProCharger and 12 psi of boost, the dyno peak readings were 1,000 lb-ft and 1,080 hp.
This charge temperature factor is a strong point of any centrifugal-style supercharger with an efficient impeller. The bottom line is that when they get going, they move more air with less heating.
That is the underlying reason why, when it comes to big mid- and top-end numbers, a centrifugal supercharger is the way to go, but should you opt for a mechanical drive (belt-driven), or an exhaust-driven turbo setup?
Like the decision between positive displacement and centrifugal, there are pros and cons for each type of drive. A mechanically driven setup definitely has no turbo lag (which is totally fixable, and is hardly an issue these days), and unlike turbos with their hot exhaust housings, suffer less underhood heat loading. That said, ultimately a turbo setup, which recovers some of the lost exhaust energy, ends up the top contender for total output. Another advantage of the turbo is that it can be sized to come on sooner with the top end boost limited by the wastegate. At the end of the day, both types will produce dazzling performance from most otherwise stock engines-sufficiently so that the problem becomes one of getting all the power to the ground. If the engine is built for supercharging from scratch, the power potential becomes near insane. A couple of projects I have personally been involved with will put that into perspective. A Mustang with a ProCharger-equipped 351 Windsor turned up the dyno rollers to 850 hp, and at that point, just smoked the tires. I estimate it was still more than 1,000 rpm from peak power. A turbocharged small-block Chevy with a Performance Techniques installation, same deal. Both of these vehicles were most certainly over 1,000 rear-wheel horsepower. Even on the grippiest road tires available, neither of these cars would hook up under 120 mph. That's on a dry road. On a wet road, you had better have a good share of Michael Schumacher's driving skills just to survive. At the end of the day, here you need to look at cost and ease of installation, as well as personal preferences when making a decision as to which type of system you should go for. If that sounds way out in left field, Underground Racing's (Charlotte, North Carolina) street turbo Viper conversion is producing over 1,800 hp at the wheels. But let's get our feet back on the ground here. A more "bolt-on" turbo kit for an otherwise stock engine such as an LS series GM, or Ford's Three-Valve, unit will respond to the tune of a 200-300 hp increase, with a boost of 8-10 psi. A good example here is the kit offered by Turbonetics for '05-08 Mustangs. This boosts rear-wheel horsepower from the stock 250-260 to about 500, and all done with less than 10-psi boost.