Pumping Iron

Pumping Iron

Bob Mehlhoff Oct 8, 2003 0 Comment(s)
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The Magna Charger MP112 supercharger features this internal vacuum-actuated bypass valve to eliminate any parasitic (pumping) loss during cruise situations.

Give It a Boost

Boost produced from a supercharger (or turbocharger) is the amount of air pressure created by the supercharger and is a function of three things: the engine's displacement, blower displacement, and the speed that the blower is turned relative to the engine rpm.

Assuming a stable speed ratio between the engine and the blower, larger blowers produce more boost than smaller blowers on engines of the same displacement. As engine size increases, boost levels drop (if the blower speed and blower size remain constant). Conversely, as engine size drops, boost moves up. For a given-size blower and engine, boost will increase by turning the blower faster in relation to the engine's speed (overdriving), and boost can be decreased by running the blower at a slower speed (underdriving). You can get the blower to run slow enough to keep the boost down to a level appropriate for the compression ratio of your engine by changing pulley diameters.

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This big-block carbureted supercharged system from Vortech provides strong horsepower gains ranging from 30 to 75 percent (depending on boost levels and tuning).

The level of boost that an engine can safely accept is primarily determined by the engine's static compression ratio and fuel octane rating. But the key to any supercharger installation is to prevent detonation. Detonation in a blown engine is more destructive than in an unblown engine, and damage to piston ring lands will occur if a blown engine is continually operated while detonating. A handy device to have with a supercharged engine is an ignition system with boost-retard control, such as the Holley PN 800-450 Ignition.

Fuel It

Without enough fuel and air, your engine can't take full advantage of the supercharger and won't make maximum boost. Remember that in addition to fueling the motor, the carburetor also acts as a restriction to air passing into the blower and engine. Under boost, the engine may need up to 50 percent more fuel and air, so it's critical to match the blower to your carburetor(s).


Adding a blower to your performance car can not only increase its power, but also impress your friends when you pop the hood. If you'd like to see what's available specifically for your engine, check out the blower manufacturer Web sites listed in the Source box, and get ready for some supercharged fun. CHP


Vortech Engineering Inc.
Channel Islands, CA




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