Introduction To Supercharging
A supercharger is the most versatile form of power adder. The power is available “on-demand” at all times, unlike systems such as nitrous oxide. Under light load conditions when the supercharger is not making boost it takes only minimal power to spin the blower. As a result in normal driving gas mileage does NOT decrease significantly. This common myth is just that, a myth. In fact, some of our customers report a slight IMPROVEMENT in fuel economy under highway conditions after a blower installation. Most likely this is due to the careful tuning that we do for our own installations.
The following topics are briefly discussed here. If you want to know what we can do for your application, call us to discuss your needs!
- Centrifugal Superchargers
- Positive Displacement Superchargers
- Water Injection
- Dynotuning and Supercharging
- Supercharger Fuel Systems
- Exclusive Offer
- Calculate Maximum Boost
Types of Supercharger- Centrifugal Superchargers
The popular ATI Procharger, Vortech, Paxton, and Powerdyne units are centrifugal superchargers. Centrifugal blowers spin at a very high speed, typically 40,000-60,000rpm. They operate like a belt driven turbocharger but do not have the severe installation and plumbing problems associated with installation of a turbocharger on a vehicle not designed to utilize one. The compact compressor is mounted on the front of the motor and is driven by a belt. On a stock motor horsepower and torque gains of 30-50% are typical. Stock drivability and emissions are maintained. The only way you know the blower is there is the marked increase in acceleration when you “stand on it”. On modified engines astounding horsepower can be achieved while remaining streetable and even pass emissions testing. Our shop has produced numerous street performance vehicles with small-block motors making over 600 rear wheel horsepower. Some have even exceeded 700rwhp. These cars have very mild camshafts, excellent manners, and are are designed to run on pump premium fuel. To see one of our street cars utilizing a centrifugal supercharger follow the link to A 4th generation F-body for the street/strip For a car used primarily for racing even more power is available, though drivability may be somewhat degraded and racing fuel may be required. We can recommend the right blower for your application and sell you the kit or provide a complete, turn-key project!
Types of Supercharger- Positive Displacement Superchargers
There are two basic types of compressor. The positive displacement type is illustrated by the Kenne Bell “twin screw” supercharger pictured to the left. With this type of compressor a fixed volume of air is delivered per revolution of the supercharger. The main advantage over other types is that full boost is available from just off-idle all the way to the redline. This makes a Kenne Bell (or other positive displacement blower) ideal for street performance cars or trucks/SUV’s. Vehicles used for towing really come alive with this type of supercharger. The added torque makes accelerating, passing, and hill-climbing effortless and expands the safe operating envelope, especially at high altitude. We have also been very successful using this type of blower in the drag racing environment. To read about one of our shop cars utilizing a Kenne Bell supercharger follow the link to Joe Zito’s “Water Injected Wonder” Joe’s car is the fastest street/strip car in the country using a Kenne Bell blower! We can install any of the commercial kits using these types of blowers or custom engineer a set up for your application. Kennedy’s has the experience, tools, and expertise to make your supercharging experience second to none!
Intake Charge Temperature and Water Injection
A characteristic of all forced induction is that it will heat up the intake charge. This decreases horsepower and can lead to detonation and engine damage as well. A well designed compressor will keep the increase to a minimum, but substantial heat is generated no matter how well the compressor is designed. This is due to the physics involved in compressing a gas and there is no way to design around it. Luckily, we can provide systems to take the excess heat out of the intake charge! We do this with either an intercooler/aftercooler setup or with water injection. Our custom water injection system was originally designed to work with positive displacement systems like the Kenne Bell or Whipple. But testing has shown that it is equally effective when used with a centrifugal blower. Many of our centrifugally supercharged cars also utilize a water injection system. We can configure and install a system for you or sell you a kit if you want to “do it yourself”.
Dynotuning and Supercharging
For all installations we strongly recommend Dynotuning to ensure safe and reliable operation of your supercharged vehicle. We can optimize your air:fuel ratio and ignition timing utilizing our extensive knowledge of both factory and aftermarket engine control systems. In addition, many owners enjoy knowing how much horsepower they have under their right foot!
Fuel Systems for Supercharging
Through extensive testing and experience we have concluded that an adequate fuel system is a key element in making power reliably with a supercharger. A supercharger pumps more air into the motor, but as Bob Kennedy often says “air doesn’t make horsepower…fuel makes horsepower”. We have found that the commonly used formulas for determining fuel requirements are often inaccurate, seriously underestimating the size of the injectors needed as well as the capacity of the fuel pump needed. It is far better to have “too much” injector and pump than too little. A lean condition can destroy a blower motor in a few seconds.
At Kennedy’s we have a wealth of experience with fuel systems. We utilize a variety of approaches to insuring adequate fuel delivery. These include the following.
- Addition of in-line “booster” pumps. This may be an adequate solution for a low boost setup on a stock or mildly modded motor.
- Replacement of the stock pump with one or more high output pumps.
- Use of voltage booster to the fuel pumps such as the Kenne Bell “Boost-a-Pump”.
- Design and installation of a complete, custom fuel system including replacement or modification of your existing fuel rails.
- Installation and tuning for larger injectors. We can install low-impedance injector drivers to allow a factory ECU to utilize injectors larger than 50lbs/h.
- Use of an FMU or adjustable fuel pressure regulator to increase fuel pressure.
- Installation of supplemental fuel injectors. These may be driven by a separate controller like the Carroll Superfueler or controlled by an aftermarket ECU.
The question “how large do my injectors need to be” often comes up in the context of discussing fuel systems for supercharged applications. As we noted above, many formulas underestimate the actual size needed. This is partially because they fail to take into account the rich fuel mixture needed when the engine is under boost. Fuel pressure is another variable. At Kennedy’s we prefer not to operate at fuel pressures much above 60psi. Injectors may operate erratically with elevated pressures and pumps may not have adequate flow. We would much rather see injectors used which are adequate for the job. The following are good general guidelines for injector sizing with supercharging, assuming one injector per cylinder.
- 30lb injectors – up to 350rwhp.
- 40lb injectors – up to 475rwhp.
- 50lb injectors – up to 600rwhp. These are the largest readily available high-impedance injectors.
- over 600rwhp – requires additional injectors or low-impedance injectors
We provide FREE Dyno testing for every supercharger purchased and installed by us. You have the satisfaction of knowing how much power you have gained and more importantly, the safe operation of your new supercharger system is verified. This can be crucial information. For example, we recently installed a centrifugal supercharger kit on a 2001 Ford Mustang “Bullitt”. The car ran beautifully after a pristine installation. However, when we put the car on the dyno using our wide-band O2 sensor we found a lean condition with the air:fuel ratio going as high as 15.1:1 under boost. This would certainly have caused major engine damage unless corrected. If the customer had done the install himself and not Dyno tested he would never have known until he destroyed his motor! We reprogrammed the factory computer and achieved a perfect air:fuel ratio. The customer was extremely pleased with the results. The car made 385hp after the install and is operating within a safe envelope.