Identifying Muncie 4 Speeds III by Paul Cangialosi

The most popular question has to be that everyone thinks they have the famous "rockcrusher" M22 4 speed. This had the same gear ratios as the M21 but with a heavy duty gearset. The reason you may ask? Well it wasn't designed so that you could go drag racing on Saturday night or impress girls in front of Burger King by doing massive hole shots. It was primarily designed as a road race transmission. The straighter angle of the gearset produced less heat and less end loading of the gear train. Combined with high impact alloy gears this 4 speed really pushed the limits of it's aluminum case in drag race applications. Although the gears are not spur gears ( completely straight ) they still produced a fair amount of gear noise thus the "Rockcrusher" name. These 4 speeds sound like a blower drive. For the real gear head the best documented movie that sports a real M22 in a car is the famous movie " Two Lane Black Top ". You can really hear this gear box howl in the background as James Taylor and Dennis Wilson talk at a little over 3 minutes in this youtube clip. Later on we get to see the same car with new paint in the classic film "American Graffiti" with Harrison Ford at the helm. Since they used a dummy car for inside dialog shots you miss the flavor of the M22 in that flick.

The dead 2.20 first gear ratio which is the same in the M21 is not that good for off the line acceleration. You would need at least a 4.56 rear end gear to compensate for the dead first gear. That was OK when gas was cheap in 1967 and you did not mind pulling 3000 RPM at 50 MPH while going to work. Times and requirements have changed making both the M21 and M22 the closest ratio production 4 speeds ever produced but also not practical for today's driving habits unless road racing is your thing. The new Muncies being built today have some better ratios.Today's examples of the new car gear set ups are Mustang GT's with a 3.35 1st gear and 3.08 rear. New Camaros with a 2.68 1st gear, 3.73 rear gear and .59 overdrive. ZR1's with a 2.68 1st gear, 3.54 rear gear and a .59 overdrive. Get the picture? If you want to learn about this stuff DOWNLOAD our RPM Calculator software for windows its free.

Top countergear is an M22. Lower gear is an M20. Notice the different helix angles of the gears.

m20 gears


Below left is an M22 1st gear. Right is an M20 / M21 1st gear.

m22 gears

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