M21 over M20 / WHY?
Thread Starter
Drifting
Joined: Oct 2007
Posts: 1,254
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From: Brown Summit North Carolina
M21 over M20 / WHY?
What would be the reason or reasons that someone would order the
M21 Close Ratio Muncie over the M20 Wide Ratio,
I understand the difference in the gear ratios in the trans, but what would someone be looking to get by selecting the M21?
Thanks
David
M21 Close Ratio Muncie over the M20 Wide Ratio,
I understand the difference in the gear ratios in the trans, but what would someone be looking to get by selecting the M21?
Thanks
David
Melting Slicks
Joined: May 2009
Posts: 3,079
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2024 C3 of the Year Finalist - Unmodified
Can't wait to see the old drag racers chime in here. Of course, who the heck is power shifting and slamming gears with a 4 speed these days. I am sure it has everything to do with getting into 2nd gear faster and not dropping too much rpm.
Tech Contributor
Joined: Jun 2004
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
M21 is the close ratio box (versus the M20). Given how a Corvette is a sports car the M21 (or M22) is preferable out on a road course where the RPMs can be kept closer during shifts (up or down). The M20 is preferable on a drag strip due to the lower first gear (and torque multiplication) to get the car moving off the line.
Race Director
Joined: Jul 2001
Posts: 15,892
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M21 is the close ratio box (versus the M20). Given how a Corvette is a sports car the M21 (or M22) is preferable out on a road course where the RPMs can be kept closer during shifts (up or down). The M20 is preferable on a drag strip due to the lower first gear (and torque multiplication) to get the car moving off the line.
Simple as that.
Safety Car
Joined: Sep 2007
Posts: 4,458
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From: Indy Indiana
The regular 4-speed M-20 has ratios of 2.52:1, 1.88:1, 1.47:1 and 1:1. The M-21 close ratio and M-22 close ratio heavy duty ratios are: 2.2:1, 1.64:1, 1.27:1, and 1:1.
a m21 has a lower 1st gear and will bog more if you have a 3.08 rear or similar.
I have a m21 sitting in my cabinet in my garage, but I don't use it since my rear end is a 2.72. If I did use it I bet I could do 75 in 1st gear. plus I would accelerate the wear on my clutch at the stoplight.
the M21 is better for the Roundy-round track crowd if you want your car set up to torque peak about mid way thru 2nd into 3rd gear.
its the closeness of 2nd and 3rd gear that makes these trans beneficial for those that need it.
the lower 1st gear and the more even spread makes the M20 more streetable.
it is almost always more practical to have a M20 for the street.
the M20 is just as durable as the M21.. it's the M22 with its straighter cut gears that make the M22 more of a heavy duty tranny.
a m21 has a lower 1st gear and will bog more if you have a 3.08 rear or similar.
I have a m21 sitting in my cabinet in my garage, but I don't use it since my rear end is a 2.72. If I did use it I bet I could do 75 in 1st gear. plus I would accelerate the wear on my clutch at the stoplight.
the M21 is better for the Roundy-round track crowd if you want your car set up to torque peak about mid way thru 2nd into 3rd gear.
its the closeness of 2nd and 3rd gear that makes these trans beneficial for those that need it.
the lower 1st gear and the more even spread makes the M20 more streetable.
it is almost always more practical to have a M20 for the street.
the M20 is just as durable as the M21.. it's the M22 with its straighter cut gears that make the M22 more of a heavy duty tranny.
Last edited by joewill; Oct 9, 2011 at 05:38 PM.
Safety Car
Joined: Sep 2003
Posts: 4,206
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From: Belmar NJ
If you had a 3.55 or lower (numericly) rear end, you'd probably be happier with the M20. If you have a 3.70 or higher (especially with an LT1 or BB) you'd want the M21 or 2. I'm sure there will be some discussion as to where I put the split in the ratios, but that's part of the fun./:\
Thread Starter
Drifting
Joined: Oct 2007
Posts: 1,254
Likes: 5
From: Brown Summit North Carolina
Thanks to all
These replies are a big help.
I have a friend that I see once a year at a major local car show,
He has a 71 LT-1 Vert with M21 and 3:55
My 71 LT-1 is a M20 with 3:70
He was asking me about the difference yesterday and I could not give a good answer, But now I can
David
These replies are a big help.
I have a friend that I see once a year at a major local car show,
He has a 71 LT-1 Vert with M21 and 3:55
My 71 LT-1 is a M20 with 3:70
He was asking me about the difference yesterday and I could not give a good answer, But now I can
David
Last edited by dmayhew; Oct 9, 2011 at 09:30 PM.
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Drifting
Joined: Jun 2003
Posts: 1,455
Likes: 5
From: Upstate South Carolina
Thnaks to all
These replies are a big help.
I have a friend that I see once a year at a major local car show,
He has a 71 LT-1 Vert with M21 and 3:55
My 71 LT-1 is a M20 with 3:70
He was asking me about the difference yesterday and I could not give a good answer, But now I can
David
These replies are a big help.
I have a friend that I see once a year at a major local car show,
He has a 71 LT-1 Vert with M21 and 3:55
My 71 LT-1 is a M20 with 3:70
He was asking me about the difference yesterday and I could not give a good answer, But now I can
David
Melting Slicks
Joined: May 2010
Posts: 3,169
Likes: 2
From: Cemetery of a town Montana
