Flywheels with two different diameters are used on Chevrolet small-block V8, big-block V8, and V6/90° engines. Large flywheels are 14" in diameter, and have 168 teeth on the starter ring gear. Small diameter flywheels are 12 3 /4 " in diameter, and have starter ring gears with 153 teeth.
The difference in flywheel diameters requires two distinct starter housings. Starter noses used with large diameter flywheels have two offset bolt holes; starters for small flywheels have two bolt holes which are parallel to the back of the block. Most Chevrolet blocks are drilled for both types of starters.