I'm currently working on my 71/72 Supreme with a 2.56 posi, and looking to put a manual into it a some point, since shifting is an important part of driving for me. I've got the crank fixed for a pilot bearing, but the only 4 speed I can find around here is a M21, close ratio. Will it be impossible to use the 2.20 first gear with the 2.56 rear and a 350? I'm afraid it will. If I was to go that route (I've had a cheap M21 offered to me, clutch and everything), I would look for an overdrive 3rd gear. The other option is a TKO, but those are expensive - I imagine the 3.27 first gear is a lot better with the 2.56 rear, though, and the .68 fifth gear would be a lot better for the 80 MPH speed limit over here.

So, in short, will a 350 be capable of working with a close ratio Muncie and a 2.56 rear without dying on me all the time?

 

I think you are going to be pretty un-happy with that combination. I'd suggest using the Muncie (if it needs a rebuild change to the 2:52 first gear). I would also suggest changing to a numerically higher rear end gear ratio. G.M. engineers liked at least 3:23 rear gears with the M21(2:20 first gear) and the M20(2:52 first gear). I had a M21 re-done and wished I would've changed the first gear to the 2:52, but I am running 4:33 rear gears and thought it wasn't that big a deal. That combo. is in my '69 W-31 race car and still needs some more guts when launching. Remember, that is a HEAVY car and not a lot of cubic inches. In the '72 442 I'm finishing up on now, I am running a warmed-up 350, M20(2:52), and 3:91 rear----should run real good.
The combination you are considering will undoubtedly be sluggish. Do yourself a favor and go through the rear now and change the ratio---it really isn't that costly----I'm sure people here will sell you parts at a very reasonable price. Look for Brian Trick here at C.O.--- he will steer you in the right direction. If the trans. needs to be gone through, do it now also---if you change the rear, the stock 2:20 first gear should be fine for normal street and "fun" driving.

 

I'll add some background info and wishes for my car to clear up the situation - I'm used to driving a 1.4 L turbo diesel - that's a 85 CUI for you Imperial types. :P So I'm not really feeling it as sluggish, even with a TH350 and that very same 2.56 rear. The gas price over here is $8 a gallon, so mileage is quite a factor, hence the desire for some sort of OD. Furthermore, buying used parts in Denmark isn't quite as easy as in the states, sadly.
That means that rebuilding the Muncie in any way is more expensive than in the states, since I need to pay shipping and import tax on any and every part I order. As it is now, I can pay $600 for a Muncie that I'll end up having to rebuild to suit my needs, as well as finding a more reasonable rear somewhere, versus buying a ready $2000 TKO and being able to leave the rest of the car alone (minus cutting the floor, but that's free) and gaining an extra gear in the process. Thoughts?

 

Wow! $8.00 for regular gas! I pay that for racing fuel (112 octane). Sounds like you really have some decisions to make. $600.00 for the Muncie isn't outlandish, nor is $2000.00 for the TKO. Have you figured in the driveshaft yoke, the length of the drivehaft, the shifter, the clutch, and the clutch pedal set-up? You are undertaking a pretty labor intensive swap, not to mention a pricey one. With the criteria mentioned, the overdrive is starting to make more sense.

 

Keep the 2.56 rear and get a Nash/Richmond street 5-speed with a 3.27 first gear, or a 3.42Z ST-10... Crash

 

Dave: No, I haven't factored in those prices, which I why I haven't bought the TKO yet. :P The labor intensive side of it isn't a big deal when I'm in the middle of a frame-off. Wish my signature worked, it'd have a link to the project thread. Half of the things you mentioned are included in the package TKO I was looking at, though.

Crash: That would work as well, if it wasn't for the fact that I've never seen a Nash, Richmond or ST-10 over here. American cars of this vintage weren't available or interesting over here until they became classics, and now they're being imported whole - so unless it was a spare when upgrading a stock car or similar, it's not available over here.

 

Seff, I speak to you as the voice of experience.

I bought a 1970 Chevelle SS (same car as the Cutlass) in 1980, when I was in high school.
It had been used as a race car, and had a 4:56 posi. rear with ladder bars, an M-21, and a 350 out of a '71 Impala under the hood.

With that rear, that 2bbl 350 could spin the rear tires all day long (and they were big racing tires). It also turned about 4,500RPM at 60MPH, and was essentially un-drivable.
It also drank gasoline at a prodigious rate.

I looked around, and happened upon a 2:73 posi. for $25, and spent a day putting it in.
Overnight, my gas mileage went up to almost 20mpg, and I could cruise on the highway all day long at about 2,000RPM.

The only disadvantage was that first gear is pretty much exactly the same as second gear in most cars. It has NO off-the-line power, and, in fact, starts rolling like a delivery truck.
I was always the only person who could drive the car, because it takes a certain amount of skill to get the 11" clutch to smoothly move the car. Once she's going, though, if you shift down, you can still snap your neck back and forth by pressing up and down on the gas pedal.

So, my advice would be that, yes, it is definitely drivable and fun with an M-21 and a 2:73, but no, it's no drag racer and will burble off the line at a green light like a truck.
I would keep the 2:73 and the Muncie for now, drive the car, and consider changes in the future, like a five- or six-speed, when you've got more money.

And, yes, I still have the Chevelle, and it still drives the same way. One day, I'll put in a different transmission...

- Eric

 

My car came with an M20 and 2.93's. It was very sluggish off the line but if it's all I had I would have kept it. You're going to have a tough time with an M21. I've since switched to 3.42's & it's just right for street driving. Why don't you just switch to an M20 input shaft. Someone else can jump in & correct me if I'm wrong but I'm pretty sure that's all you need & that will help & they are a little over $100. I've got a used one around but shipping will be more than the part is worth.

 

MDchanic: Appreciate the words of wisdom - that's why I asked, to get a second opinion.

I have more than the money needed to put in a five-speed, I'm just trying to see if I NEED to spend it (yes, my grandma was poor, so I was raised to save money) - which it very much seems like I do, I must admit, if I want to achieve the above.

Your experiences with the clutch sounds much like what starting my father's van or an old tractor is like - I could live with it, but it's not very impressive for a (huge by our standards) 5.7 L engine that sounds like a lion to perform like a sleepy kitten.

Seeing as I don't have the Muncie yet, I think I'll wait it out (which I CAN do, seeing as I have two engines, one with a working TH350) and find the best price on a 5-speed I can. The finances of this project went out the window a long time ago in favor of the thrill of having (something reminiscent of) a muscle car. Might as well spend the money I should to complete the picture. Oh well, getting the Muncie seemed like a feasible solution, so opinions were wanted. :P

allyolds68:Your info in concurrent with what I know of Muncies, but as you say, the relatively steep price will outweigh the relatively small gain, whereas with the TKO the huge price is followed by a huge gain. Make sense?

 

The M21 with a 2:56 rear will be a dud,but I think we all know that by now.I would not try & force the issue,and make those 2 work together.The M20 would be better,but you should still consider adding better gear to the rear.If you leave the rear alone,then I would look at some sort of 5-spd,whether it be a Richmond/Doug Nash,or Tremec/TKO.You can custom-order those with a variety of gear cluster arrangements.