Muncie Transmissions, Close vs Wide ratio question

[Robert M.]

At the risk of exposing myself as being dumb, i am going to as this question anyway.

Can some one explain to me the advantages of the close ratio 4 speed (M-21) vs. the wide ratio, and why the high performance cars seem to favor the close ratio?

It seems the wide ratio would launch great in 1st gear compared to a close ratio.

[Jim T.]

Re: Muncie Transmissions, Close vs Wide ratio question

My 64 was a wide ratio and my 68 is a close ratio. I do prefer the wide ratio for departures from a stop. The lack of rpm drop between gears has not been that beneficial for my driving use.

[Stuart F.]

Re: Muncie Transmissions, Close vs Wide ratio question

Oh boy! This should be interesting. Come on Duke, tell him (us) all about it!

Stu Fox

[William C.]

Re: Muncie Transmissions, Close vs Wide ratio question

The close ratio is essentially built on the "roadracing" formula that wants the engine to see even RPM drops between gearchanges during operation where the car is fairly constantly changing speed. The wide ratio configuration is more forgiving in starting off from a low speed in traffic or at a stoplight. Easier on the clutch, and with an engine lacking low-end torque easier for the driver to use. For cost considerations, GM made a decision to commonize parts as much as possible between the two versions, so where the rpm drop between gears is relatively the same percentage for all shifts in the close ratio trans, the wide ratio has a larger percentage engine speed change between 3-4 gears than the 1-2 and 2-3. That allowed only the input and cluster gears to be different between the configurations. For all practical purposes, the wide ration configuration is a much better street configuration. As I explained to a friend looking at specing out buying a '69 Z-28 many years ago, in a street race, you can always use more power off the line, and by the time you need to shift from 3rd to fourth, the race should be already over!

[Stuart F.]

Re: Muncie Transmissions, Close vs Wide ratio question

Bill;

You did it good. Tell that friend with the Z-28 not to mess with a high geared Vette from 30 on up though. From a roll he's going to get eaten up, Ha! I used to love to play that game with the 4.11's and 4.56 guys specially.

My son has had 3 of the 78 P.C.'s over the last few years, the last two being L-82's - one with close ratio, and his last one with the wide ratio. In that case, with the 3.08 finals, that wide ratio is the ticket for street driving.

[William C.]

Re: Muncie Transmissions, Close vs Wide ratio question

Actually, with a 4.10 rear and the ability to run the engine to 7000 easily, it wasn't a slouch from a roll either. He drove it a lot on trips of about 250 miles, got 16MPG on the highway at 65mph, neat car, chambered exhaust car also BTW, Nasty sounding little beast. I just about couldn't get away from maintaining it. First owner sold it to my racing partner, then it went to a fellow who was renting a room from me. Finally lost a timing chain at about 90K miles and after we replaced the timing chain it left my custody (thank the Lord) Really a quick, fun car prior to the Arab Oil Embargo!

[Duke W.]

Re: Muncie Transmissions, Close vs Wide ratio question

The only difference between WR and CR is the countergear ratio, which makes the first three gears of the WR shorter by an equal percentage than the CR, and the 1-2 and 2-3 intergear ratios are the same for both.

But since fourth in both is direct, the is a HUGE 3-4 gap in the WR, but it's as close as the others on a CR.

The CR was designed for use with torque shy SHP/FI engines with a short axle ratios.

The WR is more practical for medium performance engines and taller axles. There are three gears for "fun" and one for cruise. The WR is like a five-speed direct drive (fifth) gearbox that's missing fourth gear.

With a short axle the CR is like a five-speed with no fifth and like a five-speed with no first with a tall axle.

Duke

[Joe L.]

Re: Muncie Transmissions, Close vs Wide ratio question

My 64 was a wide ratio and my 68 is a close ratio. I do prefer the wide ratio for departures from a stop. The lack of rpm drop between gears has not been that beneficial for my driving use.

Jim----


I think your experience sums it up perfectly.

[Bill M.]

Re: Muncie Transmissions, Close vs Wide ratio question

My '65 with an L78 had a close-ratio and 3.55 rear axle. Those huge intake ports resulted in poor throttle response. I replaced the close-ratio with a wide-ratio and the car now drives like a close-ratio 4.11...perfect.

[Duke W.]

Re: Muncie Transmissions, Close vs Wide ratio question

The Super T-10 that was used on Corvettes beginning in the mid-seventies and is still produced by Richmond Gear has a better ratio set with the biggest gap between first and second where it is relatively transparent.

The best transmission gearing is when the gaps close (tighter intergear ratios) as you work up through the gears. The tighter the intergear ratio, the less revs fall off between gears. Revs pick up in the next gear equal to the shift point divided by the intergear ratio. The intergear ratio is computed by dividing the lower gear ratio (higher numerical value) by the next higher gear ratio.

T-10 WR: 2.56, 1.89, 1.51, 1.00:1
Super T-10 WR: 2.64, 1.75, 1.34, 1.00:1

(Muncie first, second, and third are slightly different than the T-10 - only in the second decimal place.)

The intergear ratios are 1.34, 1.25, 1.51:1 and 1.51, 1.31, 1.34:1, respectively.

As a point of comparison the BW T-50 gearing in my Cosworth Vega is 3.41, 2.08, 1.40, 1.00, 0.80:1, and it's coupled to a 4.10 axle with 22.5" tires. The intergear ratios are 1.64, 1.49, 1.40, 1.25. Modern small sedans have similar transmission gearing, but taller final drive ratios.

The CR versions have a first gear ratios of 2.20 and 2.43 with the same 1-2 and 2-3 intergear ratios.

For the way most of us use our vintage Corvettes (cruising around town and road trips) the Super T-10 WR set with a tall to medium axle ratio would be a better combination than any T-10 or Muncie.

In most industrial gearbox applications the ratio is determined by dividing the output shaft speed by the input shaft speed. In an automotive transmission this would result in gear ratios less than one for most gears and greater than one for "overdrive" gears.

I suppose the automotive marketing guys figured that typical consumers would have a easier time dealing with "multiplication factors" (numbers greater than one) than output/input speed ratios.

Duke

[Michael H.]

Re: Muncie Transmissions, Close vs Wide ratio question

My '65 with an L78 had a close-ratio and 3.55 rear axle. Those huge intake ports resulted in poor throttle response. I replaced the close-ratio with a wide-ratio and the car now drives like a close-ratio 4.11...perfect.

I have a 66 425 HP, 2.20 1st/close ratio and a 3.70 read. For me, that's the ultimate for a big block cruiser.

[Bob S.]

Re: Muncie Transmissions, Close vs Wide ratio question

At the risk of being criticized for not reading much of this thread (which I haven't), and possibly repeating what someone else has already said....

The choice of grearing is a compromise, and a close rato gearbox is better suited to an engine that has less "torque spread" (as Duke likes to call it). This keeps the torque available at the rear wheels (a product of the flywheel torque times the multiplication thru the transmission and axle) higher after each shift than would be the case with a wider ratio transmission.

This is not as important with an engine with a wider torque spread such as a '60's big block or the well engineered engines (LSx) of today....

Bob S.

Actually, considering the torque spread (or the lack of it) with my '03 Honda S2000, the torque spread of my L-79's is pretty generous and makes the close ratio M21 seem much less necessary.....

[Michael H.]

Re: Muncie Transmissions, Close vs Wide ratio question

At the risk of being criticized for not reading much of this thread (which I haven't), and possibly repeating what someone else has already said....

A close rato gearbox is better suited to an engine that has less "torque spread" (as Duke likes to call it). This keeps the torque available at the rear wheels (a product of the flywheel torque times the multiplication thru the transmission and axle) higher after each shift than would be the case with a wider ratio transmission.

This is not as important with an engine with a wider torque spread such as a '60's big block or the well engineered engines (LSx) of today....

Bob S.

Actually, considering the torque spread (or the lack of it) with my '03 Honda S2000, the torque spread of my L-79's is pretty generous and makes the close ratio M21 seem much less necessary.....

Youse guys are making this way too complicated. I just like hearing the even RPM spread while going up through the gears. (not racing or acting like a kid)
Like listening to the off road exhaust in nice even notes.

[Bob S.]

Re: Muncie Transmissions, Close vs Wide ratio question

Bill;

You did it good. Tell that friend with the Z-28 not to mess with a high geared Vette from 30 on up though. From a roll he's going to get eaten up, Ha! I used to love to play that game with the 4.11's and 4.56 guys specially.

My son has had 3 of the 78 P.C.'s over the last few years, the last two being L-82's - one with close ratio, and his last one with the wide ratio. In that case, with the 3.08 finals, that wide ratio is the ticket for street driving.

Hi Stu - Experience with my '68 Z/28 w/4.10's and M21 differed slightly: It outran the following: Boss 429 Mustang, GTO, 383 Road Runner and numerous others. In each case, the same result happened several times during the same "meeting" at speeds up to maybe 100 mph. Small block Vettes were never any problem (although I'm sure a '70 LT-1 would have been a problem!), and I owned the Z and a '67 L-79 Vette together for 7 years. I guess the result would have been different if the encounters continued beyond the Z's 130 mph top speed @ 7000 rpm, but none did....

I did behave myself in the presence of Hemi's and 427 Vettes, though.

One particularly embarrassing memory: On the second day I had the Z/28 in 1971, a man in a big Olds with his family (wife, kids and all) beat me from a roll @ maybe 30-40 mph. That's when I learned the DZ 302 just wouldn't pull below 3000 rpm at WOT, and I should have down shifted a couple of gears before going. (The previous owner had installed mechanical secondaries on the Holley to make matters worse!)

Regards,
Bob

[Bob S.]

Re: Muncie Transmissions, Close vs Wide ratio question

Youse guys are making this way too complicated. I just like hearing the even RPM spread while going up through the gears. (not racing or acting like a kid)
Like listening to the off road exhaust in nice even notes.

Mike - I agree 100%!! The even gear spacing of the close ratio box is especially nice for matching revs during downshifting going into a corner.