David DeCan

Need some opinions on the matter. Car is 70 Convertible that I am cloning into a W-30. 455 medium to mild. 450 hp/500 torque. Rear "O" type posi with 3.23's. Car will never see a drag strip. Want it to be a fun stop light to stop light car as well as a Montana Interstate 90, 80 MPH cruiser. Changing to car over from TH 350 Auto to a stick. Doubtful I will ever put an overdrive in car. Probably a 15x7 inch SS wheel. 27 inches tall.

Question: Which Muncie best fits my needs? I have never had a 4 speed, 455 Olds Car. Always wanted one. Don't know which 4 speed best fits. Thanks for your input.

David

Chesrown 67 OAI

with a 3.23 rear and not racing you would want the wide ratio Muncie, (M21). It has 2.54 1st gear. The close ratio 2.20 1st gear Muncie is for use with a 3.90 or lower rear gear.

My442

The 4th gear on all is 1 to 1, so the cruising part will be the same.


The M20 is the wide ratio model, with a lower first gear and a wider spread between gears, This transmission works best with rear end ratios lower numerically that 3.55. (3.08, 3.23).


The M21 and M22 are close ratio models, with a lower numerically first gear, and closer spread between gears. This transmission works best with higher numerically rear end ratios (3.73, 3.91, 4.11).


The other differences are the input and output spline counts, and how the shifter attaches to the transmission.


I would recommend the M20 for your combination.

My442

This is not correct.


The M20 has the higher number first gear, and the M21 and M22 have the same 2.20 first gear.


The difference between the M21 and the M22 is the ways the gears are cut. A M22 is heavier duty and has a distinctive whining sound, which people thought sounded like a "Rock Crusher"

David DeCan

Thanks.

Is the M20 with 3.23's going to "fun" off the stop light?

joe_padavano

^^^This.

An even better choice, if you can find one, is the Super T10 with the 2.88 first gear (the M20 has a 2.52 first), as found in Firebirds and Camaros.

Chesrown 67 OAI

Never could keep them straight! Thats why i stated the gear ratio that i was suggesting to use -- call it a typo"

Chesrown 67 OAI

Joe - Ive acquires a 2.88 Super t-10 for use in the Ramrod Joe!! I also have the higher Super T 10 ( i think about 2.43?) that i could use. Im gonna use 4.66 gear.
Gonna use one and sell the other.

vette442

I have the 455/M20/3:23 combo on one of my cars now, and I've had it in three other '72s (two 455/M20/3:23s, one 350/M20/3:23s).

The answer was "yes" for all of them. Maybe not quite the same as my W-31/M21/3:91s, but that's more a result of the engine and rear gearing I think.

Terry

Octania

You can think of it this way


If you have a lot of torque multiplication in the final drive gearset already- performance gears of ratios numerically larger than 3.5 or so...


then you don't need as much torque amplification in first gear to get going. Therefore the Manual Trans gear 1 ratio can be more like low 2's rather than the high 2's. Low 2's is closer to the 1:1 gear-4 ratio. Thus the term "close ratio" for M21/M22.


And, yes, the M20 with gears on the performance end of the economy range will be quite satisfying as you bring on the engine from a stop.

David DeCan

"Quite satisfying." Very good. Thanks guys. David

VC455

Wide ratio Muncie has the same geometric ratios between the first three gears as the two close ratios. This means the rpm drop from first to second and second to third is identical among the three transmissions. The wide ratio Muncie has a big drop between third and fourth--not the best at the drag strip.

For a street transmission, there are no downsides to the wide ratio only the upside as Chesrown 67 noted.

My442

Multiply the transmission first gear times the rear end ratio.

Close ratio - 2.20 x 3.23 = 7.106

Wide ratio - 2.52 x 3.23 = 8.139

The ideal number is 10, so a higher number means more torque multiplication.

My old 442 had a 2.20 first gear and a 3.91 rear end. Tons of fun around town, but not really good on the highway.

oldsmobiledave

All these posts & no one has mentioned tire height.


You can talk all you want about trans gear ratios & differential ratios but without knowing your tire height all your calculations are in vain.


26" tire? 27" tire? 28" tire? Well, which is it?


To calculate torque multiplication & cruise RPM you need to know all three components; trans gears and differential gears & tire height.


Rant over.


ps...can we talk about cam shaft specs & vehicle weight not too if we really want to build a well balanced driveline?

joe_padavano

So long as you prefer sound over performance...

Sorry, but I have to disagree. You can ABSOLUTELY compare the relative benefits of different effective final drive ratios, assuming tire size is the same. The OP never asked about changing the tire size, and no matter what the tire size, a steeper first gear will improve acceleration.

Additionally, going from a 26" to a 27" tire makes less than a 4% difference in effective final drive ratio. Selecting an M20 over an M21/22 makes nearly a 15% difference. Pick the 2.88 first Super T10 over the M21 and it's a 30% difference.

oldsmobiledave

Yes if you want to establish a tire height then you can compare relative changes effected by the various trans ratios & gear ratios but ignoring the effects of tire height leaves you vulnerable to having a mismatched driveline combination.


The way a car runs at the track with a 28" tall tire is very different than a tire of the same width but only 26' tall. The cruise RPM at any given speed is also effected and the faster one goes the bigger the effect.


If you want to ignore tire height in your calculations feel free. Those who desire the best matched driveline components will include it.

David DeCan

RPM at 80 MPH is important to the person who made the original post, but it is not the whole game. Stop light to stop light "fun" is also in the equation. Tires have not been purchased. 15x7 Olds Rallys will be used. Will probably go with the tallest and widest tire that will reasonably fit in all four wheel wells without scraping or rolling the fender lips.

27 inch tire with 3.23's gives approximately 3200 RPM at 80 MPH. 28 gives 3100. 29 gives 3000. Loosing 100 RPM approximately for every inch of tire diameter.

So I think with the M20 and 3.23's I am in the game.

Can I get a 28 or 29 inch diameter tire on all four corners without scraping?

Also like the idea of a bit more tire height for header and oil pan clearance--live on a gravel road with some big road humps

joe_padavano

Please go back and read the very first post in this thread.

1) This may be hard to believe, but not everyone is building a max performance drag car.

2) Without an OD trans, top gear will ALWAYS be 1:1, so tire size is irrelevant when selecting a trans for highway RPMs unless the rear end ratio is changed, which the question did not address. It's 3.23:1.

3) I don't care what the tire size is, you DON'T want a 2.20 first with 3.23s. There's a reason why the factory never sold this combo.

4) As I pointed out, the tire size will make less than a 4% difference in RPMs. You'll be hard pressed to feel that.

Certainly if I were building a competitive quarter mile car, I would consider ALL aspects when selecting driveline and engine components to maximize performance. For a nice street cruiser, that isn't necessary, and frankly, overcomplicates things. Given the reality of a limited budget and parts in hand, you do the best you can by making reasonable judgements.

The alternative is to study something to death, which is why NASA can't do anything anymore...

joe_padavano

David,

255/60-15s are about the tallest you can run on the front without scraping. These are a hair over 27" tall. You have more flexibility in the back if you want, but the tallest reasonable T/A are 275/60-15 (at 28") or 255/70-15 (at 29") for the 4x4 look.

As you point out, even the 29" tires provide such a small difference in RPMs, you won't feel it. Keep in mind that taller tires negate your gear ratio advantage, however small that difference might be, so you've got competing requirements. An OD trans is the only way to fix this right.

Ryan 1969 Chevelle SS396

I love this discussion!!!!!

Can I thread steal?

Lets talk about my car..............................

69 W-31, M20, 3.42 anti-spin, Sports Coupe that is light on options, (haven't looked up what the car weighs yet but no modifications so it should be the same as whatever GM rated them at) 14 X 6 steel wheels with F-70-14's, or G-70-14's (G-70 as PSMCDR allows one size up) I am excited to drive it as every bit of internet information I find says this will be a nice street-able combo. Nice first gear take off with 8.75 torque multiplication factor.

I haven't researched the tire height yet or rpm calculator at highway speeds in fourth 1 to 1 yet....

Ryan

PS: In a year or two I plan to spice things up with a PSMCDR specific engine, and an M22, and a "Chevy" 4.56 rear...... that should get the conversation started;-)

oldsmobiledave

Look at the new Auto Gear case M-22 4 speeds. Much better than original.


You don't need a Chevy rear Ryan. Some well spent money on good parts & a set of 4.33 or 4.66 gears for your Type O will keep it all Olds.


Good luck & have fun with the car.

Ryan 1969 Chevelle SS396

Thanks for the info:-)

I already have the M22, August 69 OTC replacement. (Kind of too nice to drag race with............ but I own it so the price is right....)

I have heard 'o' type are weak...... 10 bolt...... please enlighten me. (I was impressed when i took apart my TM code rear and found no C clips, if the axle breaks the wheel will stay on the car:-) That is a weak point of a Chevy......

I would much prefer to build a killer Olds 4.66 rear....... are there build up articles here somewhere I can rear over? (I am search deficient..... I am bad at finding old articles for some reason)

Ryan

oldsmobiledave

Send a PM to 507OLDS or MONZAZ with your concerns about the Type O.


You would be further ahead selling your M-22 to someone for a period correct resto & invest in one of the Auto Gear versions.

joe_padavano

Let me suggest that you move the rear axle discussion to the Drivetrain/Differentials sub-forum instead of hijacking the OP's thread on Muncie four speeds.

Ryan 1969 Chevelle SS396

Good point,

Ryan

David DeCan

As someone pointed out this thread has been extremely helpful as I assembly this 70 Convertible. Thanks to all who participated. David

z11375ss

Do yourself a BIG favor and go with a Tremec 5 speed. I really like mine as you can drive around town like a 4 speed and have an overdrive (.64) on the highway. The best of both worlds. I'm running 3.73s and loving it.