Supercharger/driven pulleys are only 1/3 the diameter of crank/drive pulleys and therefore spin at approximately 3 times the speed of the crank – 750 ft/sec. This equates to over an 1/8 mile per second! That’s a lot of heat and friction. Could that be why the OEM’s use steel pulleys. We use only durable long life high grade plated steel except in a special 10 rib Shelby application.

It’s common practice to switch pulleys to vary boost levels for street, weekend racing etc. Kenne Bell Steel Pulleys can be quickly and easily replaced with one bolt using the Kenne Bell Pulley Wrench (Twin Screw) or the Kenne Bell Billet Pulley Puller (Eaton). Stock Eaton pulleys are pressed on, constructed of relatively soft high lead material and are therefore easily bent by “old style” pullers when removed. Reinstallation is also difficult, requiring a press if a good installation tool is not available. Kenne Bell Steel Pulleys are virtually indestructible. Big selection. Precision machined steel and plated for corrosion resistance.

WARNING: USE ONLY KENNE BELL STEEL SUPERCHARGER PULLEYS ON OUR SUPERCHARGERS. USING ANY OTHER PULLEY WILL VOID THE WARRANTY.

PULLEYS, RATIOS & BOOST – See chart for boost numbers. Plus (+) psi boost numbers (+2 psi, +5 psi etc) is a non scientific, inaccurate and confusing method of rating pulleys. At Kenne Bell, we prefer to also use “ratios” (crank pulley ÷ supercharger pulley = ratio) to describe a potential boost increase. In other words, list the boost AND ratio. Why? Is a supercharger pulley a +2 with the stock 7.5“, 9” or ? crank pulley? And is the +2, +4, +6 crank pulley with a 3.5“, 3” or 2.7” supercharger pulley?

To make matters more confusing some superchargers, such as the Eaton, do not develop the same boost at 2000, 3000, 4000, 5000 and 6000 rpm. They suffer from “boost drop off.” For example: What plus (+) pulley rating do you give a Cobra ‘03 pulley that is 15.3 psi at 4000 but only 10.3 at 6000 when the stock pulley was 8.3 at 4000 and 7.8 at 6000? We refer to the stock pulleys as a 2.11 ratio and 7.8 psi (7.5” ÷ 3.55” = 2.11 ratio) and the 3” pulley as a 2.5 ratio and 10.4 psi (7.5” ÷ 3” = 2.5 ratio). Now take the same 3” pulley with a 9.25” crank pulley and you have a 3.1 ratio instead of a 2.5 ratio. On our superchargers, that’s around 6 psi variance. Get the point? Kenne Bell lists the ratios and boost for all applications.

Note: Boost pressures are to be used as a guide and may vary **Boost pressures will vary with inlet restriction. For comparison, all tests were conducted with stock inlet systems. For example: with a 2.75” pulley, ‘03 Cobra boost will increase approx. 2 psi with Kenne Bell Cool Air Kit.