What is a muncie rockcrusher 4 speed?

The Muncie Rockcrusher 4-speed is a high-performance manual transmission used in various Chevrolet muscle cars, particularly from the late 1960s to early 1970s. It is known for its durability and ability to handle high horsepower, featuring a distinctive "whine" in its operation due to its straight-cut gears. The Rockcrusher designation specifically refers to the M22 variant, which was designed for racing and high torque applications. Its robust construction makes it a popular choice among car enthusiasts and restorers today.