2:73 gears with Muncie 4 speed

1980RS

Veteran Member
Jun 17, 2006
6,399
MN
My 2nd gear in the T-56 is 2.20 and I really do not have much trouble taking off with it, but I have a stock Vortec 350 in front of that trans so it has a lot of low end torque.
 

tom3

Veteran Member
Aug 1, 1999
14,677
ohio
I was thinking back to a 283 with a Duntov cam, M21 with a road gear didn't work for that. 4.11 gear really woke that car up. Not so hot on the highway though.
 

70Znut

Veteran Member
Lifetime Gold Member
Feb 5, 2016
342
Sarasota,FL
I have a 68 Camaro m21 with 3:55 gears and my 70 m22 with 3:73 gears.
Both cars very snappy off the line.
The 68 originally had 3:08's and the 3:55 upgrade made a big difference.
If you'll be doing any major freeway driving I thin the 3:55's a better option.
If you more a light to light, in town drive I'd do the 3:73's.
Any more gearing than that in a Muncie might be a bit much, at least for me.
Then again a Tremec TKX with 3:73 is best of both worlds, if it's in you budget.
 

pooch400

New Member
Feb 21, 2012
28
waterbury
I don’t mind changing rear end ratio as I planned on adding a posi carrier anyway. After doing a little research on the net it looks like the m21 was never designed for freeway gears. My decision now I guess is 3:73 or 4:11 gears.
Don’t forget to take rear wheel diameter into consideration when choosing your final gear ratio.
I don’t mind changing rear end ratio as I planned on adding a posi carrier anyway. After doing a little research on the net it looks like the m21 was never designed for freeway gears. My decision now I guess is 3:73 or 4:11 gears.
I just finished a year long 70 Z28 build and have questions about gear ratio.
The car was a father/son project that sat for about 10 years before I purchased it. I am not sure if it is a real Z28 as I don’t have a trim tag and it was a Los Angeles built car.

It has a CTB stamped block with 186 camel hump heads, and an original polished winters intake. The trans. Is a Muncie close ratio 4 speed. Also has a floor mounted gas pedal.
The rear end I am assuming is not original to the car and is a 10 bolt open rear end. I calculated the rear gear ratio at about a 2:73 as it is revving about 2500 rpm at about 65 mph.

My question/ issue is it is a complete slug off the line and needs a good amount of RPM to take off from a stop. Once moving it seems to go pretty good.
Is a 2:73 rear not compatible with the Muncie gearing?

I do plan on changing the rear to a 3:55, or 3:73 with posi. Would this make a huge difference on acceleration from a stop?
That is a beautiful car.
I just finished a year long 70 Z28 build and have questions about gear ratio.
The car was a father/son project that sat for about 10 years before I purchased it. I am not sure if it is a real Z28 as I don’t have a trim tag and it was a Los Angeles built car.

It has a CTB stamped block with 186 camel hump heads, and an original polished winters intake. The trans. Is a Muncie close ratio 4 speed. Also has a floor mounted gas pedal.
The rear end I am assuming is not original to the car and is a 10 bolt open rear end. I calculated the rear gear ratio at about a 2:73 as it is revving about 2500 rpm at about 65 mph.

My question/ issue is it is a complete slug off the line and needs a good amount of RPM to take off from a stop. Once moving it seems to go pretty good.
Is a 2:73 rear not compatible with the Muncie gearing?

I do plan on changing the rear to a 3:55, or 3:73 with posi. Would this make a huge difference on acceleration from a stop?
That is a beautiful Camaro. Don’t forget wheel diameter. My 1980 Z28 4 speed had 3.90 gears, 245/60/15 tires, (26.6 inch diameter), and ran 3200 Rpm’s at 65mph 3450 at 70mph. If you want rapid acceleration and 2550 Rpm at 65mph. An overdrive transmission with a .68 overdrive and 4.56 gears will do it. You’ll also want your cruise rpm slightly above the Rpm your cam starts making power. All calculations based on a 26.6 diameter wheel. Good luck figure out what works best for you.
 

Bentley

Veteran Member
Aug 14, 2020
265
The first question I would ask you is what kind of driving are you going to do with this car?? Lots of recommendations on here without any idea of what you will use this car for or how you will drive it.....
If your final drive " guesstimate" is correct, that is a pretty poor gear ratio for anything
Sounds like your cam is a bad pick for a street car..
More info needed here....
 

third_edition

Veteran Member
Lifetime Gold Member
Feb 7, 2004
102
Braeside, Ontario, Canada
Hi,
Just a couple of things...

- M21 and M22 have different gear sets, so it is important that you confirm which transmission you have.
- If it is an M22 (close ratio) it is fairly easy to tell, there is a drain plug in the bottom and the straight cut gears have a very distinctive whine to them (in low especially) - you can also look at the numbers.
- I don't believe that you could even buy an M22 close ratio trans with gears higher than 3.73 from the factory, in 1970, because of the low first transmission gear.
- Try this calculator to determine vehicle speed, in different gears, with different components...

((1/rear end gear ratio) x (3.14 x tire diameter) x ((rpm / trans ratio) x 60))) / 63360 = speed (mph)
Eg. for a car with a 3.73 rear gear, 25.65" dia rear tires, running at 4000 rpm, in first gear (2.64 ratio) the calculation would be ... ((1/3.73)x(3.14x25.65)x((4000/2.64)x60))/63360 = app. 31mph
Change the numbers for fourth gear (1.0 ratio on a 4 spd) ... ((1/3.73)x(3.14x25.65)x((4000/1)x60))/63360 = app. 81mph

- I believe you can find most of the trans gear ratio info on this site, for various transmissions, or do a search - these numbers are readily available.

Cheers,
George
 

kdsracing

Member
Mar 13, 2009
58
Apple Valley, CA
I don’t mind changing rear end ratio as I planned on adding a posi carrier anyway. After doing a little research on the net it looks like the m21 was never designed for freeway gears. My decision now I guess is 3:73 or 4:11 gears.
You will regret 4:11gears. I wouldn’t recommend 3:73 without overdrive if you plan to drive freeways. Had 3:73’s in my ‘70 with a TH 350 trans and it was fun until I wanted to travel the freeway. I put in a Bow Overdrives Stage 3 200 R4 trans and love it.
I would stay with a 3:55 with your Muncie. It is a good compromise for performance and sustained high speed driving. It was a common combination from the factory.
And I wouldn’t downgrade from a great transmission to a mediocre T10 especially if yours is an M21 or 22.
 

RTSE

Member
Apr 11, 2020
85
I just finished a year long 70 Z28 build and have questions about gear ratio.
The car was a father/son project that sat for about 10 years before I purchased it. I am not sure if it is a real Z28 as I don’t have a trim tag and it was a Los Angeles built car.

It has a CTB stamped block with 186 camel hump heads, and an original polished winters intake. The trans. Is a Muncie close ratio 4 speed. Also has a floor mounted gas pedal.
The rear end I am assuming is not original to the car and is a 10 bolt open rear end. I calculated the rear gear ratio at about a 2:73 as it is revving about 2500 rpm at about 65 mph.

My question/ issue is it is a complete slug off the line and needs a good amount of RPM to take off from a stop. Once moving it seems to go pretty good.
Is a 2:73 rear not compatible with the Muncie gearing?

I do plan on changing the rear to a 3:55, or 3:73 with posi. Would this make a huge difference on acceleration from a stop?
Nice Camaro, I have 8.5” 10 bolt with a Trutrack & 3.91 gears. Car gets off the line hard and just hooks up and goes straight with no wheel spin. Freeway driving 60mph is a little over 3000 RPM and when you stand on it chucks you back in the seat
 




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