M20 or M21
Drifting
Joined: Jan 2012
Posts: 1,908
Likes: 129
From: Fredericksburg Virginia
Both have a 1:1 final drive.
1st, 2nd, and 3rd have more gear in an M21 vs. an M20. For example, and M21 with 3.36 gears can do 66 MPH in 1st at 6,000 RPM vs. 59 MPH with an M20. Similar changes in 2nd and 3rd.
The operative thing here is that the M21 was called a "close ratio" option. That meant that there was not as large of a gap between 3rd and 4th, which works well for a race track. That was the REALLY neat thing about these cars...they were thinking about "track options" when they were designed and assembled.
The problem is that the "close ratio" came at the sacrifice of the painfully tall 1st gear. 1st gear in my M20 is already extremely tall. I could not imagine adding another 10% more gear to my 1st. It just isn't playful enough. Considering I have a well-over-400-but-not-quite-500-hp engine in my car, that would mean anything less would just be slow, slow, slow.
The thought Mr. Revi has of "gearing down" an M21 doesn't make any sense to me. You would simply be obliterating driveability at 60 MPH since the final drive is identical (2,450 RPM with 3.36 gears vs 3,050 RPM with 4.11 gears). There just isn't enough operative gain at the low end to have this strategy make any more sense with an M21 than an M20.
There is no significant change or "strengthening" between the two gearboxes. This is unlike the M22 which has the straight-cut 1st gear.
For all these reasons, I would choose an M20 over an M21 for street use, given the choice. I'd have to do A LOT of street racing...not autocrossing...street racing on high speed circuits...to justify the odd gearing on the M21.
All this said, I am removing my M20 in the forseeable future and installing a TKO600. No other way to go, in my opinion. Playful in 1st and long-legged in 5th. Tie that to a big gear in back, and it's the best of all available worlds.
Just my thoughts.
...not that I've pondered this issue at length or anything...
1st, 2nd, and 3rd have more gear in an M21 vs. an M20. For example, and M21 with 3.36 gears can do 66 MPH in 1st at 6,000 RPM vs. 59 MPH with an M20. Similar changes in 2nd and 3rd.
The operative thing here is that the M21 was called a "close ratio" option. That meant that there was not as large of a gap between 3rd and 4th, which works well for a race track. That was the REALLY neat thing about these cars...they were thinking about "track options" when they were designed and assembled.
The problem is that the "close ratio" came at the sacrifice of the painfully tall 1st gear. 1st gear in my M20 is already extremely tall. I could not imagine adding another 10% more gear to my 1st. It just isn't playful enough. Considering I have a well-over-400-but-not-quite-500-hp engine in my car, that would mean anything less would just be slow, slow, slow.
The thought Mr. Revi has of "gearing down" an M21 doesn't make any sense to me. You would simply be obliterating driveability at 60 MPH since the final drive is identical (2,450 RPM with 3.36 gears vs 3,050 RPM with 4.11 gears). There just isn't enough operative gain at the low end to have this strategy make any more sense with an M21 than an M20.
There is no significant change or "strengthening" between the two gearboxes. This is unlike the M22 which has the straight-cut 1st gear.
For all these reasons, I would choose an M20 over an M21 for street use, given the choice. I'd have to do A LOT of street racing...not autocrossing...street racing on high speed circuits...to justify the odd gearing on the M21.
All this said, I am removing my M20 in the forseeable future and installing a TKO600. No other way to go, in my opinion. Playful in 1st and long-legged in 5th. Tie that to a big gear in back, and it's the best of all available worlds.
Just my thoughts.
...not that I've pondered this issue at length or anything...
Last edited by keithinspace; Jun 7, 2016 at 09:08 AM.
Burning Brakes
Joined: Apr 2008
Posts: 776
Likes: 96
From: Plymouth MN
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Drifting
Joined: Jan 2012
Posts: 1,908
Likes: 129
From: Fredericksburg Virginia
I have 3.36 gears behind my M20.
I could not fathom 3.08 for the same reason that I don't have M21 envy...1st doesn't need to be any taller.
If I were building a fresh diff and was heavily committed to my 4-speed, I would maybe consider a 3.55 rear gear. MAYBE even a 3.70. I think a 4.11 would be too much, though. Just too much RPM at cruise.
I'd say 3.36 or 3.55 is the sweet spot as far as making the most of a Muncie.
I'm planning on running 4.11 or 4.33 gears with the TKO600, though. It's gonna be sick.
I could not fathom 3.08 for the same reason that I don't have M21 envy...1st doesn't need to be any taller.
If I were building a fresh diff and was heavily committed to my 4-speed, I would maybe consider a 3.55 rear gear. MAYBE even a 3.70. I think a 4.11 would be too much, though. Just too much RPM at cruise.
I'd say 3.36 or 3.55 is the sweet spot as far as making the most of a Muncie.
I'm planning on running 4.11 or 4.33 gears with the TKO600, though. It's gonna be sick.
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Safety Car
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I think that dissertation was informative and summed it up.
I learned something today. Thanks for the thread ? OP.
Thanks Keith for the answer.
Marshal
I learned something today. Thanks for the thread ? OP.
Thanks Keith for the answer.
Marshal
Both have a 1:1 final drive.
1st, 2nd, and 3rd have more gear in an M21 vs. an M20. For example, and M21 with 3.36 gears can do 66 MPH in 1st at 6,000 RPM vs. 59 MPH with an M20. Similar changes in 2nd and 3rd.
The operative thing here is that the M21 was called a "close ratio" option. That meant that there was not as large of a gap between 3rd and 4th, which works well for a race track. That was the REALLY neat thing about these cars...they were thinking about "track options" when they were designed and assembled.
The problem is that the "close ratio" came at the sacrifice of the painfully tall 1st gear. 1st gear in my M20 is already extremely tall. I could not imagine adding another 10% more gear to my 1st. It just isn't playful enough. Considering I have a well-over-400-but-not-quite-500-hp engine in my car, that would mean anything less would just be slow, slow, slow.
The thought Mr. Revi has of "gearing down" an M21 doesn't make any sense to me. You would simply be obliterating driveability at 60 MPH since the final drive is identical (2,450 RPM with 3.36 gears vs 3,050 RPM with 4.11 gears). There just isn't enough operative gain at the low end to have this strategy make any more sense with an M21 than an M20.
There is no significant change or "strengthening" between the two gearboxes. This is unlike the M22 which has the straight-cut 1st gear.
For all these reasons, I would choose an M20 over an M21 for street use, given the choice. I'd have to do A LOT of street racing...not autocrossing...street racing on high speed circuits...to justify the odd gearing on the M21.
All this said, I am removing my M20 in the forseeable future and installing a TKO600. No other way to go, in my opinion. Playful in 1st and long-legged in 5th. Tie that to a big gear in back, and it's the best of all available worlds.
Just my thoughts.
...not that I've pondered this issue at length or anything...
1st, 2nd, and 3rd have more gear in an M21 vs. an M20. For example, and M21 with 3.36 gears can do 66 MPH in 1st at 6,000 RPM vs. 59 MPH with an M20. Similar changes in 2nd and 3rd.
The operative thing here is that the M21 was called a "close ratio" option. That meant that there was not as large of a gap between 3rd and 4th, which works well for a race track. That was the REALLY neat thing about these cars...they were thinking about "track options" when they were designed and assembled.
The problem is that the "close ratio" came at the sacrifice of the painfully tall 1st gear. 1st gear in my M20 is already extremely tall. I could not imagine adding another 10% more gear to my 1st. It just isn't playful enough. Considering I have a well-over-400-but-not-quite-500-hp engine in my car, that would mean anything less would just be slow, slow, slow.
The thought Mr. Revi has of "gearing down" an M21 doesn't make any sense to me. You would simply be obliterating driveability at 60 MPH since the final drive is identical (2,450 RPM with 3.36 gears vs 3,050 RPM with 4.11 gears). There just isn't enough operative gain at the low end to have this strategy make any more sense with an M21 than an M20.
There is no significant change or "strengthening" between the two gearboxes. This is unlike the M22 which has the straight-cut 1st gear.
For all these reasons, I would choose an M20 over an M21 for street use, given the choice. I'd have to do A LOT of street racing...not autocrossing...street racing on high speed circuits...to justify the odd gearing on the M21.
All this said, I am removing my M20 in the forseeable future and installing a TKO600. No other way to go, in my opinion. Playful in 1st and long-legged in 5th. Tie that to a big gear in back, and it's the best of all available worlds.
Just my thoughts.
...not that I've pondered this issue at length or anything...
Safety Car
Joined: Jan 2008
Posts: 3,794
Likes: 430
From: Aarhus, Denmark
If it is a 300/350 engine, and if a 5 speed is considered, then a TKO 600 is a very strong transmission, a smaller transmission can be considered, unless a engine upgrade is on the wish list also.