The amount of boost you can run is directly related to an engine's static compresssion ratio. When the boost is combined with the compression ratio, the result is the effective compression ratio. Typically, a 5- to 8-psi boost range (usually produced with the supplied pulleys in blower kits) will work fine for compression ratios in the 8:1 to mid-9:1 range (operating on 91/92-octane fuel). However, this will ultimately depend on other modifications to the car, manual or automatic transmission, gearing, operating temperature, vehicle load, and altitude. If detonation is encountered it can often be controlled with boost retard devices or by experimenting with different-sized pulleys.

Special Carburetion
Choosing a carburetor or fuel injectors is a crucial step when building a blower-specific engine, because under boost the engine will often need 40-50 percent more fuel and air. Unlike a normally aspirated engine that may suffer only low power from poor fuel delivery, a supercharged engine without enough fuel under power may run extremely lean and destroy the engine. Running too small a carburetor also means that you can't flow enough air to produce maximum boost.

Because more fuel is required to feed a supercharged engine, the fuel-delivery system must be considerably improved. This means large fuel lines of AN-8 or bigger, properly selected and installed fuel pump(s), an adequately designed tank, full flowing filters, and a correctly wired electrical system to operate the fuel pumps.

Blow-Through Carburetion
On a blow-through supercharger system, the carburetor can either reside in a pressurized box or utilize a special carburetor hat. Under boost the false atmosphere (pressure being blown into the carb) requires revamping many of the original carburetor designs to properly supply fuel. A blow-through carburetor generally features sealed caps on the metering blocks, the main well, and the idle well. These carburetors typically feature only annular boosters so that as the signal gets stronger more fuel flows into the engine. As boost is increased by each psi, fuel pressure must too be increased at the same rate. To do this, a special regulator is referenced to boost pressure and raise or lower the regulated fuel pressure, depending on demand.

Turn Back
Reverse-rotation superchargers are generally used in applications where there are fitment issues or on engines designed to spin opposite of most other engines. Fitment issues arise when the area behind the belt driveline is impacted. Examples are 32-valve cylinder heads and exhaust manifolds. In this case the supercharger is mounted in front of the belt line. Consequently, the supercharger must now be rotated in a reverse motion, in which case manufacturers design the inner components of the blower as a mirror image of a standard unit.

Ignition Systems with a Supercharger
On any blown engine, high-performance ignitions are required primarily to provide adequate spark at higher-than-normal engine pressures and speeds. Additionally, it is often a good idea to run spark plugs that are one to two ranges colder than normal. Rule of thumb: the more boost, the colder the plug required.

One of the most important concerns with any supercharger installation is detonation control. This is because under acceleration, detonation can damage the piston ring lands (or other worse yet, damage rod bearings, destroy pistons, or blow head gaskets). A handy device to counteract most detonation problems is an ignition system with a boost-retard control.

Ignition timing is especially critical with a supercharger to not only keep detonation at bay, but also provide good power. For most applications, the distributor should have a centrifugal advance mechanism set up so that the entire advance is in by 2,500 rpm. Typically, 34 degrees should be a safe level of ignition lead to provide close to optimum performance.

There is a lot of power to be gained with a supercharger. The biggest problem, if you can call it that, is selecting the right unit. Although there's little guesswork, and every manufacturer can direct you to a system that'll incorporate all of your needs. Detailing some of the differences is just the beginning, and if you've never experienced a blown car yourself, it's definitely something to be had. During our research for this story, we had the opportunity to ride in Mike Fossati's '64 Chevelle (equipped with the featured 8-71). The power and acceleration was absolutely unnerving. Nailing the throttle produced a hair-raising jolt, and besides making lots of power the supercharger sure pulled a crowd when we had the hood up.