I am in the middle of rebuilding my Muncie M-21. I am glad I decided to do it myself. Watched the video, found some step by step instructions. Piece of cake so far and a lot of fun.

But I have been questioning lately whether or not this close ratio trans with it's 2.2 first gear is actually going to get me what I want. I would appreciate any insight.

What I have:
Muncie M-21 close ratio; 2.2, 1.64, 1.28, 1.00
3.73 rear end.
Small block 383, about 380 hp. with a Engle EP-22HYD - 230/480 cam. Power band on this cam is 1800-5800.
BF Goodrich radial TA's on the stock 15 inch x 8 Inch wheels.

What I want:
The intent was to build a very good LOW end of the RPM range performer. I want to have fun off the line at the red lights and just tooling around town. Once in a while I want to be able to make noise, smoke whatever. Yes, just like when I was a dumb kid! I'm WAY WAY more interested in my 0-60 times than what happens over 60 or 70. Make no mistake, I do want the performance from a standing start to scare me a little, or at least put a smile on my face.

Here are some options I came up with for comparison:
M21: 2.20 1st x 3.73 = 8.20
M20: 2.52 1st x 3.73 = 9.39
Richmond: 2.89 1st x 3.73 = 10.78 (plus advantage of overdrive, .77)

I have been told in the past that the M21 will be the best choice and a lot of fun. But I thought 10:1 is the best ratio choice for off the line? That would make the M21 the least option. What am I missing here? I need some education on this stuff. Please direct me to a link or provide guidance.

 

The M 21 was for road racing. It kept the engine in the narrow rpm band when racing at speed. It is not the best for 0 to 60 sprints. The gearing in 1st is just not there. The M 20 is a much more street friendly combo with its 2.52 1st gear. Sure the M 21 will work and you have decent torque to get it moving but for street fun the lower 1st gear of the M 20 will be more fun.

 

You can 'roast' the tires now. Putting in a lower first gear would just make the tires have less grip. Your tires are now the limitation from having better launches. But, if you install tires with better grip, then you will begin damaging other drive train components (unless you have already upgraded them). If I were you, I'd keep what you now have....

 

go with the wide box if you want low or off the line performance, the only draw back is the rpm drop from 3rd to 4th......

 

Everything everyone said is good info.,and correct,but I have a 302 w/alittle bigger cam,aluminum heads,and 6x2 holleys on a crossram,M21,and 3.55s out back,and set it side ways in 1st,and 2nd whenever I want,and running 255/60/15s on all 4 corners.
You have alot more torque.Let your motor do some work.

 

Can you clarify? My son and I disagree on if you mean to go with M21 or M20? I think you mean the engine is powerful enough to handle the M21 gears without bogging down. So take the 2.2 1st. gear, M21 for actually better performance.

 

Alan.....I'm not saying better performance,cause the M20 will give you a better first gear ratio,if this is what you are after.In all actualality...w/what you described...the M20 is a better boulevard cruiser for what you described,but...what I was saying....you have a M21 now,right?W/your engine combo,and the rearend gears.....you will have a VERY respectable,and fun little stop light bruiser.That's what I was saying.
My engine is mostly in the higher rpm power band,but I still can come off the line sideways,whip it into a 180,360,whatever I want then set it sideways coming out of it in 2nd too,and my car is at best...a high 12 second car,and no bottom end torque.
It's all about what you want to do w/it,and what you are really after.I went the other end of the spectrum,and like to drive,shift,and corner,but your engine will work for you w/the 3.73s,and a clutch.
That was my point.
I'd love to sell you one of my Richmond,or Tremec set ups,so you can acheive a few more points on paper,but you are throwing money away for what you described what you are after.
Kevin

 

Kevin,
I respect your honesty. My problem is I have almost no reference point to compare to. I haven't been in such a car for many years. Modern Vettes yes, but not 60's 70's vintage. It is all abstract in my mind so it is hard to decide. But your saying from a practical standpoint to just use what I have because both will probably give me what I want. Coupled with my lack of experience there is even less chance that I would know the difference anyway. The only reality I do know is if I decide I don't like it after a season or two I can simply spend $600 on a new gear set and convert to a M20 over a winter. Not a big deal. I guess I have decided,, again,, that I will keep what I have and move on.
thanks!

 

what flywheel are you running?

 

I have a similar dilema with my '69 project. Original car was M/21 with 3:70 rear and 350 small block. I decided to go M/20 on my recent 350 build only because I am gonna run a light 15lb flywheel and figured I'd need the 2.52 1st gear to help with the loss of inertia when getting off the line from a dead stop. Seems like the M/20's came on the base small block cars (lowest hp/tq) for good reason.

But...........seeing as the stroker 383's are all about torque if I were you I'd be tempted to give the M/21 a shot. With the 3:70 rear and the standard 383ci 400ft/lbs at 2000rpm you should be fine with the M/21.

Let us know how it works out - when I get my car running I'll post feedback on the M/20.

Good Luck, Ed

 

It's a deal

 

With your 383 low rpm torque engine build and 3.73 gear the M21 will work fine. It will roast the BFG's at will.

 

Thanks Mako, I respect your opinion. We will see what happens!

 

Alan...I really do think that you will be happy w/your combo.
On this forum,or any other car forum...it is so easy to loose sight,and want to change up because of all the different setups on here,and the knowledge these guys have,and that is great,but it is also,easy for one to get away from what they had in their sites to try to build/replicate what the next guy is doing.And....that is only natural,but not always needed.
These are GREAT cars,they look awesome,get alot of attention,and it doesn't take a whole lot to make them fun little cruisers,and stop light bruisers.
I can appreciate the being away from them,and having no base line to go by.I was away from them for many years,and only lived on a distorted memory,but they don't change,and before all this technology,5-speeds,6 speeds,fuel injection,better clutches,and on,and on.....these were awesome cars.Fun cars,and that is what it is all about.
Plus....you have a 68,so I am ALL smiles for you,and your boy!!!

 

A very old,and very,very light Harvey aluminum w/brass insert.

 

I appreciate the voice of reason. I also love the distorted memory comment. So true with cars and many things in life.
Our lack of knowledge with these cars makes us spend more. That can keep potential enthusiasts out who think they don't have enough knowledge of funds to partake.
I try to research and also ask the same questions over and over weeks or months before I get to that stage in the project. It may frustrate some people but by the time I actually get to that stage I am pretty comfortable with the path I want to take.
I feel pretty confident about the tranny choice and rational behind it.