Topic: M20,21,or 22
in Forum: C3 Driveline Components
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Lifetime MemberEquinunk, PA - USA
Joined: 10/31/2007
Posts: 2471
Vette(s): 1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.
I have a base car. 72 350. The transmission has/is 11inch fine spline aluminum case. The tank sticker says BASE for transmission. The question I have is what one is it? 20,or 21. I doubt it is a 22. Close or wide ratio? It seems high on bottom end, not much pizzaz. Top end is good and gets in the area of 18 MPG. IDEAS? THANKS Mark
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Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20218
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
"Base" or standard equipment 4 speeds were the wide ratio, M20 transmissions. They do have a better 1st gear ratio than the M21....2:56 compared to a 2:20. 
Joel Adams
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Frederick, MD - USA
Joined: 9/8/2003
Posts: 3398
Vette(s): 1969 convertible L71 427/435 4-speed black interior
My '69 has the M21 close ratio...very little spread in gearing at all...even in slow to moderate driving I'm banging gears fast. Bang, bang, bang and I'm in 4th. Actually, unless I'm on an upward slope, the car doesn't really need 1st and 2nd gear. Starting out in 3rd is no trouble at all.
Lifetime MemberHot Springs, AR - USA
Joined: 4/24/2004
Posts: 3236
Vette(s): 69 Conv #'s match 427, TKO-600/.64, 3.36HD-Posi, HT, T/T, PS, PB, PW, SP, Leather, Comp XE264HR & Roller Rockers & Lifters, Air-Gap RPM intake, Holley St Av 770 VS, MSD 6AL+Dist+Blaster SS, K&N, Jet-Hot Hooker Side-Pipes, Steeroids, Al Rad, Spal Fans
[QUOTE=Gunslinger]My '69 has the M21 close ratio...very little spread in gearing at all...even in slow to moderate driving I'm banging gears fast. Bang, bang, bang and I'm in 4th. Actually, unless I'm on an upward slope, the car doesn't really need 1st and 2nd gear. Starting out in 3rd is no trouble at all.[/QUOTE]
this is the entire reason I am not installing my M21 in my car. I am leaving it on the shelf and maybe one day ill get Adam to rebuild it just for thoroughness since the numbers match.
the close range is useless for a car that you actually drive.. I found I usually shifted 1,3,4 or just 2,4
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Mounds View, MN - USA
Joined: 5/24/2007
Posts: 1031
Vette(s): 70 LT1 coupe, 69 350 HP coupe, 69 390HP 427 coupe, 71 LS5 convert, 85 coupe, 93 coupe
The tank sticker on my '70 has a column(the second from the left), with the option number. In my case it says 03M21AA, for the M21 close ratio. I believe '72s used the same format.
Larry
Larry
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Oak Creek, WI - USA
Joined: 5/21/2008
Posts: 1965
Vette(s): 1981 Great White Shark. Red Interior, 350/190 hp. PS, PB (SS), A/C CC, T-Tops. Served three years in Active Duty Army, then Retired Air Force after 34 years! Badger State Vettes Car Club. 175,000 Original miles!! Now own a 1998 C-5!
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Dan
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Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20218
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
The close/wide ratios have more to do with the spread between 3rd and 4th than anything else. On the wide ratios, shifting from 3rd to 4th is an incredible drop in rpm, compared to the close ratio.
The close ratio idea was to use a low rear gear(for bottom end help), and keep the engine in it's powerband during the shifts to the next gear up, OR down.
The wide ratios are much better suited to normal, "daily" driving, imho.
The close ratio idea was to use a low rear gear(for bottom end help), and keep the engine in it's powerband during the shifts to the next gear up, OR down.
The wide ratios are much better suited to normal, "daily" driving, imho.
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Lifetime MemberEquinunk, PA - USA
Joined: 10/31/2007
Posts: 2471
Vette(s): 1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.
I have nothing in the space after transmission. Only the word base. Guess I have a M20-wide ratio. Thats good as far as I am concerned. I am looking for mileage for the most part, not smoking tires. THANKS to all! Mark
Lifetime MemberHot Springs, AR - USA
Joined: 4/24/2004
Posts: 3236
Vette(s): 69 Conv #'s match 427, TKO-600/.64, 3.36HD-Posi, HT, T/T, PS, PB, PW, SP, Leather, Comp XE264HR & Roller Rockers & Lifters, Air-Gap RPM intake, Holley St Av 770 VS, MSD 6AL+Dist+Blaster SS, K&N, Jet-Hot Hooker Side-Pipes, Steeroids, Al Rad, Spal Fans
in reality mileage wont matter which one unless its all stop and go. the top gear is 1:1 in all 3.
Lifetime MemberEquinunk, PA - USA
Joined: 10/31/2007
Posts: 2471
Vette(s): 1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.
WOW! that is a statistic I was not aware of. THANKS Good to have that info stored away.
in Forum: C3 Driveline Components
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