M20 compared to M21

[73c34me]

Hello, Would like some thoughts on this combo. I have the M20 installed and an M21 on the shelf, that i would like to try.

1973 Vette, 3100 lbs. 4.1:1 R&P. 12:1 383 Stroker motor. Issues
Upon take off, I shift into 2nd nearly after the clutch is completely out
Upshifting from 3-4 at high rpms is difficult. Downshifting at speed from 4-3 is like hitting the brakes...
I don't race the car but enjoy spirited driving and the occasional 1/4 mile test and tune.
Also, I would like the clutch to last..

thanks.

[In-Tech]

Are the splines the same, I remember my 73 camino came with m21 and fine spline input(26 I think) and T400 large size output shaft.

[Rick!]

Muncie Identification Article

[novadude]

M21 will have a taller 1st, 2nd, 3rd gear compared to the M20, and the ratio spread from 3-4 will not be as wide as compared to a M20. With 4:11, it seems like the M21 would be a better fit in that light car. No worries about excessive clutch slipping with that much gear in the rear. The M21 should allow you to actually use 1st and not shift as soon as the clutch is out, and the tighter 3-4 spread with the M21 should help with the "hitting the brakes" feeling on a 4-3 downshift.

[discloseenjoin]

Muncie Identification Article

The information is not overly focused. I couldn't come up with a solution.

[tjs44]

For street driving I like the M20 as I could pretty much go from first to third around town driving where with the M21 you pretty much had to gothru all the gears.Tom

[panic]

The "wide" ratio box has 2.52:1 1st gear, the "close" is 2.20:1.
"Close" only refers to the 3-4 shift, the RPM loss on the 1-2 and 2-3 shift are the same for both.
With tall (numerically low) axle, the 2.20 is a pain to drive in traffic. For a 9:1 overall SLR/crawl ratio, the close box needs 4.09 axle, the wide 3.57.