Adjustable Timing

Changing engine combinations in order to run today's pump gas usually results in running a stock camshaft that is no longer optimized for the motor.  To help boost either the low-end performance, or get back some of the top-end power, PMI has developed adjustable timing pulleys.  These pulleys come in two types: Fixed position and infinitely adjustable.

7-Position

The 7-Position Cam Pulley is of the fixed type with seven positions. Each of those positions allows you to advance or retard the camshaft in discrete steps, from –16° to +16° in increments of about 3°. (Crankshaft degrees.) Advancing the cam generally improves low-end torque and throttle response; Retarding the cam generally improves starting behavior and top-end performance. The principal benefit of fixed-position adjustments is the ability to revert back exactly to any previous setting. 

7-Position Cam Pulley installed in Steve Stone's 1967 Firebird with a 1969 250 OHC motor

Slotted Vernier

The Infinite Resolution Cam pulley can be set to advance or retard camshaft timing with infinite resolution between -10° and +10° (Crankshaft degrees.)  The principal advantage of infinite resolution is the ability to fine-tune the camshaft timing to desired performance, either through on-vehicle testing, or on the dynamometer.

Rob Egbert's OHC motor with shorty headers and the Vernier adjustable cam pulley