View Full Version : What are overdrive pulleys?

10-28-2002, 06:59 PM
An overdrive pulley is the pulley that drives the supercharger. The aftermarket
offers two popular sizes of overdrive pulleys that are smaller in diameter than
the stock pulley. The idea is that if the overdrive pulley is smaller, the
crankshaft can spin it faster (via the supercharger belt). One pulley size is
called the 5% pulley or “SVO” pulley. It spins the supercharger approximately
5% faster which will result in an additional 2psi of boost. You should expect a
gain of 10HP, but at the expense of reduced supercharger longevity and an
increased risk of blowing a head gasket.

The other pulley available is called the 10% pulley. There are several
manufacturers of this pulley and as you can tell from the name, it will drive the
supercharger 10% faster. These pulleys offer up to a 3psi increase in boost,
which is noticed by a gain of 15-20HP. This pulley is not recommended for
engines with high miles or ones that are not mechanically sound. The risk of
head gasket failure is dramatically higher with a 10% pulley and this is typically
a $1200 repair job. DO NOT install one of these on your car without first
knowing the risks. If your car has been modified with a substantially improved
exhaust system, then the risk of head gasket failure is minimized. The use of
headers and an exhaust system with larger diameter pipe is highly