All About Pulleys

Pulleys are critical engine components and are often misunderstood by racers.

You have read articles about them, seen them in catalogs and heard other racers discussing the use of them but you're really not clear as to what the difference is in a 1:1 and reduction pulley setup.

The pulleys that are on the crankshaft and water pump come in a variety of sizes, but what matters is the ratio between the two.

A 1:1 set will have a crank and water pump pulley of the same diameter, resulting in one revolution of the water pump for each revolution of the crank. Regardless of the size, as long as the two pulleys are the same diameter you will get the same effect. This setup is advised on engines running RPM's below 7600-7800 as well as those using a multi-pass radiator.

A reduction setup is used to slow down the water pump in an effort to keep it within optimal operating RPM range. It does this by utilizing a water pump pulley that is larger in diameter than the crank pulley. This is recommended on engines running high RPM's.

To calculate the speed of the water pump at any given engine speed, simply divide the crank pulley diameter by the water pump pulley diameter. Then, multiply by the engine RPM. Example: A 4'' crank pulley ÷ 5'' water pump pulley = .8 × 1000 crank RPMS = 800 water pump RPMs or a reduction of 20%.