takin directy from MMandFF.com
its long but a very good read.
dont be shy of a supercharger
All About Blowers
The ins and outs of compressing air.
Photography: Courtesy of the Manufacturers
There are hordes of late-model Mustang owners who will swear a blower is the only way to fly. These folks have felt the magic of supercharging, be it the sight of an intimidating polished huffer, having heard the inrush of air whistling at high pitch, or perhaps they have felt the good graces of g-force created from boost and unchained horsepower.
Ah, yes, superchargers, those miraculous devices that can easily double the power of a stock engine or help you build a beast capable of 2,000 hp or more.
Today, with technology being so advanced, making those ponies is not all that hard. But there's a science to how it all works and it takes a bit of knowledge to make big power and keep it alive. And that science involves getting the air into the cylinders and providing the best diet of fuel, timing and octane.
Ever since the late-model Mustang gained huge popularity in the mid-'80s, the supercharger has been one of the most sought-after, add-on accessories. Back in the day, blowers were far less common than they are today. They had an almost mystical aura about them, even in the early '90s. Today, you can only describe their popularity as a mania. We at MM&FF know how popular they are, because over the course of each month we get dozens of letters and e-mails asking about superchargers and the effect they will have on a particular car or engine. The questioning includes, "How much power will a blower add? Will a blower hurt my engine?" And, "Which is the best one?"
I'll tell you right off the bat that we've yet to find one single "best" supercharger. This may disappoint those looking for a clear-cut winner, but the bottom line is that most blowers work well, both in theory and practice, and all have good points and bad. And, while there are ways to directly compare blowers, it's more important to understand how they work and what to expect from each one. Different vehicles may benefit from one type or another so it's important to know what you're looking for.
When picking a supercharger, you'll need to consider the size of the unit, the type of drive system, airflow potential/boost capabilities and the drive speed. In addition, consider the weight of the vehicle, transmission type, gearing and the manner in which the vehicle will be used. Is it a drag-only vehicle or is it mainly street driven? If it's heavy, like a Lightning, it will love low-rpm torque, and if it's light (3,000 pounds or less), it can afford to give up on torque in order to make more high-rpm horsepower.
There are enough types, sizes, makes and models to confuse even the brightest blower backer. Superchargers are relatively simple machines, however, finding maximum power and keeping the engine alive is a different thing entirely. This part of the equation is complicated indeed, but we plan to diffuse the important facts and expose the myths. So fret not fearless Stang bangers, because in the next few pages we plan to take a journey through the land of supercharging. But we caution you. Reading this may just "force" you to get blown.
A supercharger, by definition in Webster's Dictionary, is "an apparatus consisting of a pump, compressor, or blower used to increase the volume of air over and above that which would normally be drawn into an internal combustion engine due to the action of its pistons."
When the engine is naturally aspirated it relies on the pumping action of the pistons to draw air into the cylinders. The negative pressure in the cylinders combined with the ram effect of the intake manifold, camshaft overlap and exhaust scavenging, allows each cylinder to draw in the air/fuel mixture every time the intake valve opens. With supercharging, air is constantly being packed into the intake manifold under pressure (called boost), so the air is forced into the cylinders when the intake valve opens, rather than being drawn in solely based on the pressure differential between that of the cylinders and the atmosphere in the manifold. This additional air provided by the supercharger simply permits the engine to burn more fuel, thus creating more cylinder pressure and, with any luck, more power. Supercharging is really that simple--on the surface.
Since a supercharger is a compressor driven by the crankshaft, the output of the blower changes with rpm (speed). Generally, the output will increase until the point of peak efficiency, and then output falls off. Eventually the blower will reach the point where it makes no more boost, just extra heat.
Supercharging has been around for quite some time and has been used on all types of engines, including piston-driven aircraft and generators in big industry. In auto racing (and in high-performance street applications), we've learned to apply supercharger technology to help our internal combustion engines achieve incredible power levels. With a blower, volumetric efficiency can easily exceed 100 percent, while most naturally aspirated engines struggle to achieve 60-80 percent VE.
Another benefit is that owners can retain the stock cam, heads and, in some cases, the induction system, therefore, retaining much of the OE driveability, yet still realize a huge increase in performance.
The most extreme supercharged engines can be found in drag racing, namely in the Top Fuel and Funny Car ranks. These extreme machines utilize 500-cubic-inch engines with hemispherical combustion chambers and they burn a specialized fuel called nitromethane. Using large 14-71 Roots-style blowers, these "fuel burners" produce 45-50 psi of boost and generate upwards of 8,000 hp. Today's Top Fuel cars run quarter-mile times in 4.40s at speeds over 330 mph.
A good portion of the massive power comes directly from the fuel and its explosive force. Unlike leaded racing gasoline, nitromethane carries its own oxygen and requires a nearly equal 1.7:1 air/fuel ratio. Compare that to a gasoline-burning supercharged engine that will require a 11.5-12.0:1 a/f ratio.
At wide open throttle, the nitro burner's fuel flow is equivalent to a garden hose with the nozzle held wide open--and that's per cylinder. If you've watched drag racing on TV you've seen the header flames, but at times there is raw fuel pouring out of the headers during a run. The engine is said to have "dropped a cylinder" and it happens when the spark plugs can no longer light the massive quantity of fuel. This can lead to all kinds of problems. One is engine hydraulicing and that's often followed by a massive explosion and ensuing fireball. But Top Fuel engines aren't the only supercharged beasts that go boom in the night when things go wrong.
We've seen many Mustangs and Lightnings have failures as a result of boost, however, this isn't a fair way to explain all the blow-ups. Read on and I'll explain. Remember one of the questions that I said we often get, "Will a blower hurt my engine?" The answer here is yes and no. (And I'm not trying to be a wise guy, either.)
First I'll cover the "yes." A supercharger can cause engine damage that otherwise wouldn't occur, but the common failures (blown head gaskets, cracked blocks and burned pistons) are often the result of a poor engine tune-up, gasoline with insufficient octane rating, abuse from the driver or any combination of the three.
"First off you have to consider the condition of the engine," stated Ricky Best, the Race/Media Relations Manager for Vortech Engineering. "Most bolt-on systems making about 8 pounds of boost are designed and tuned to be able to be applied to completely stock, as well as modified engines, without having any adverse effects on the motor itself. If the engine is ailing or high in milea