I am just finishing up the restoration of my 67 442. It has a basically stock 455 except Edelbrock 750 and headers. It has the original 4 speed muncie and a new standard/stock clutch. It is VERY sluggish on take off. There is some slight chattering in the clutch, but otherwise feels fine. I do want to mention that the rear wheels are 20 inch with 255/45 tires. The rear end is stock. Do I have a clutch/transmission problem or do i have a rear end gear ratio problem. The 455 engine seems to run beautifully. Any help or suggestions are appreciated. I don't know what gear ratio the car has but if that is my likely problem, what should I change to? I have a 10 bolt rear end and would like to keep it. Thanks in advance!

 

I don't understand the sluggish statement. Are you saying the engine does not seem to have power or ???.

 

The online calculator I found shows that is a 29" tall tire, which is several inches taller than factory, but still I am surprised that a 455 / 4 speed setup would have any issues with even that tall of a rear tire.

To determine your rear gear ratio, drive at a steady speed in 4th gear and see what the engine RPM is. With this info you can use an online calculator to determine the rear gear ratio.

 

OldCutlass, by sluggish I mean its very slow on take off from first gear. it's almost as though I'm trying to take off in 3rd or 4th gear.

 

You did not say what distributor or what timing settings your using?

You can determine your gear ratio by counting the number of turns your drive shaft make per 1 revolution of the rear axle. For instance, if the drive shaft rotates three and a quarter turns to one axle rotation, then your rear axle gear ratio is 3.25:1.

 

It is possible your trans is the close ratio (2:20) Muncie, that coupled with a rear end ratio of around 3:08 or higher, means very slow starting out of the gate.

 

How would I know if i have the close ratio Muncie? Any Idea what I would look for to determine? Thanks

 

Those tires will make about a 10% difference in the effective rear axle ratio as compared to the stock 26.5" tires. In other words, if the axle ratio was 3.08 (as an example), with those tires that would be the same as 2.73 with the stock tires. Definitely not helping. Was this always a four speed car?

 

a close ratio with 3.55s is going to be sluggish on take off,especially with that tall of tire.i just swapped a close ratio out for a wide ratio for the exact same reason.huge difference in 1st gear. i don't believe you can tell which trans you have without removing it and putting it in 1st gear and count the turns.you can't go by the grooves in the input shaft.i have muncies with 1,2 and no grooves.knowing your gear ratio would help for starters.

 

29" tall tires, unknown rear gears, unknown transmission, unknown cam? Not sure how one can restore a musclecar, and not know these things, but if you're running 29" tires, W30 cam, M21 Muncie and 3.08 gears for instance, you're gonna have a problem...

 

Sounds like the same problem I’ve had with past M21 transmissions. As noted above the 1st gear ratio is 2.20 and it sounds like you have poorly mated rear end ratio like a 3.08 or even a 3.42. Easiest solution is to put a taller rear end gear like a 3.91. Then your combined ratio would be 2.20 X 3.91=8.602. You generally want a total ratio above 8 for overall drive ability. My W31 came with 3.91’s originally (TO rear end) and the previous owner put 3.42’s in. Even with 3.42’s it was lame off the line in 1st gear. I put 3.91’s back in. What a difference. The M20 (2.52 1st gear) is actually a better choice for cars with 3.42 or less rear end gears 2.52 X 3.42=8.6184. Al

 

One other popular solution to this issue is to convert your M21/22 to a wide ratio by buying a new wide ratio gear set. Then you keep the benefit of the a more user friendly highway 3.08-3.42 gear set but get moving off the line like you have taller rear gears. I did this with the M21 in my 1970 442 which had 3.42 rear gears. The Italian gear set I bought had a 2.54 1st gear. Great drive ability with a 8.6868 total ratio in 1st gear. Al

 

Check the passenger front side of your axle tube for a stamp and hopefully you can determine which rear end gears you have. Then decide which route if any makes sense for you. the 2.20 first gear is a problem with crappy rear end gears like 3:08's or even worse 2:73's. That first gear really needs at least a 3:55 or even better 3:91's. Al

 

A steeper first gear helps takeoff and clutch life. In the mid-70s I went to 2.78 then 2.88 first gear. I also recognized that a closer 3-4 spread helped, and picked transmissions with 1.34-1.39 third gears. That is the problem with the M20--a big 3-4 gap. BTW, the 66 W30 came with M21 and 4.11 gears for a 9.04 overall ratio with admittedly short 14" tires/wheels. Olds did want to use the 2.78 first gear 4-speed Ford "Dearborn" transmission like they did the Ford 3-speed, but GM wouldn't allow it.

 

While input is helpful, this is a 4 year old thread and the OP had not been on since 2018.