Hey guys. I would like another gear but don't know what that will accomplish. Currently have a 400 stock engine w/ 067 heads 3 speed manual tranny and 355 rear gears. rear wheels are 24" tall.It is mostly for in town crusin. Twice a year its a fifteen mile cruise to a local car show.I like how it gets up and goes in 3rd or 2nd but!!! crusin in 3rd gets loud and old. Anyone have a decent suggestion on a close or wide ratio 4 speed? I dont have a clue.
I too like the 3-speed manual - should be the Ford Dearborn 3-speed which is the heavy duty version adapted to be used by Pontiac, and why the bellhousing has 2 bolt patterns as the main case attachment "ears" are different than the Muncie. The dis-advantage is that you don't have that extra gear to drop down into if you are rolling along and are challenged. From a dead stop, the 3-speed can take advantage of Pontiac's torque and you'll never miss the extra gear.
With 3.55's, you can use any of the Muncie transmission, M-20, M-21, or M-22. The M-20 is considered a "wide ratio" transmission with a 2.52 first gear. These work OK with as low as a 3.23 gear in the rear, although you can certainly go lower, but it takes a little more slip of the clutch to get rolling. The M-21 is considered a "close ratio" transmission with a 2.20 first gear. The M-22 was used in big HP/torque applications and is a "close ratio" transmission like the M-21. It has straighter cut gears so it has an iconic whine that many like to hear being inside the car and is easily identified just by its sound alone.
M-20 gear ratio - 2.52 -first, 1.88 -second, 1.46 -third, 1.0 -fourth
M-21 & M-22 - 2.20 -first, 1.64 -second, 1.28 -third, 1.0 -fourth
Grooves on the spline of the input shaft can identify all three of these units.
1963-65 M20 2.56 ratio 10-spline 7/8-in. shaft - no grooves- 27-spline output shaft
1966-70 M20 2.52 ratio 10-spline 1-in. shaft - 2 grooves - 27-spline output shaft
1971-74 M20 2.52 ratio 26-spline 1-in. shaft - 2 grooves - 32-spline output shaft
1963-65 M21 2.20 ratio 10-spline 7/8-in. shaft - 1 groove - 27-spline output shaft
1966-70 M21 2.20 ratio 10-spline 1-in. shaft - 1 groove - 27-spline output shaft
1971-74 M21 2.20 ratio 26-spline 1-in. shaft - 1 groove - 32-spline output shaft
1965-70 M22 2.20 ratio 10-spline 1-in. shaft - no groove - 27-spline output shaft
1971-74 M22 2.20 ratio 26-spline 1-in. shaft - no groove - 32-spline output shaft
GM made it a little easier to identify these transmissions when they started using a letter designation on the end of the build code on 1969 models:
A- M20 2.52 ratio (wide)
B- M21 2.20 ratio (close)
C- M22 2.20 ratio HD (close)
The M-20 would be the more plentiful to find/purchase, the M-21 harder to find/purchase, and M-22 very rare. They do make an aftermarket M-22 with improvements, but not inexpensive and not really needed unless you have some serious HP/torque and like to race with it.
So best application for your car would be the M-20 unless you simply want a close ratio M-21. I had a factory M-21 in my '67 GTO which had the factory 3.90 rear. The close ratio keeps the RPM's higher up in the power band with each shift and there is little spread between the gears - thus the "close ratio" designation.