Quote:
Originally Posted by Formulajones
Lust4speed is correct.
Having both M-20's and M-21's I can tell you, for an M-21 to be as quick you need to have a pretty good gear in the back. The M-20's are just quicker and you don't need as much rear gear to do it. By the time you're rolling 80+ mph for 4th gear, the rpm drop in the M-20 is less of an issue anyway with momentum.
I've run that setup with SBC's and even with less torque, the M-20 going into high gear was never an issue. And the nice thing about it, since I didn't need as much rear gear with it, it was a better highway cruiser than the M-21.
But like I mentioned earlier and Lust4speed has touched on, the TKO is a much better choice that covers both ends of the spectrum and will completely change the car and the driving experience.
I understand you'll have to do what your budget allows.
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Now this is news to me! The M21 with its close ratio gears is FASTER than the M20. I've had two cars. a M20 with a 3.55 rear and a M21 with a 3.90 gear. The shift from 3-4 really dropped the rpms' in the M20 where it was not nearly as bad with the M21. Don't let anyone kid you, the M21 with the right rear gear will keep the rpm's up in the HP range better than a M20 and is faster. Much more desirable Muncie. If you get a chance to read the 4-part series on Project Judge in the 1969 Popular Hot-rodding magazine, they used both Muncie trans. The M21 was faster and they go into reasons why as they were building up to a RAIV engine and drag car from originally a RAIII 3 spd car. Generally speaking, M21 trans are more expensive from collectors than a M20 for obvious reasons.