Hot Rod Forum banner

1 - 9 of 9 Posts

·
Registered
Joined
·
4 Posts
Discussion Starter #1
Hello there,
I have a 1955 Chevy 3100 step side pickup that is 100% all original. I am building a 327 motor for it. It will have 2.02 160 aluminum heads, a Holley 750 double pumper, a weiand dual plane intake, headers, and a nice mild can of sorts. Run at about a 5500-6000 redline. I want to put a Muncie four speed in it. I know the 5speeds are more economical but I love the old Muncie's feel, so no changing my mind there. I would like to know what the best rear end ratio would be for that motor/tranny combo for street use would be. I want to be able to show the truck has some balls, but want to be able to drive it comfortably on the street. Also, what would be the best Muncie? (M20,21, or 22) I know the ratio varies based on which tranny it is. Any tips are much appreciated. Thanks.
 

·
Hotrodders.com moderator
Joined
·
9,581 Posts
You can use some of the speed calculators to play with gearing. Shows rpm at a certain speed with a certain gear ratio and tire height. Generally in a street rig we look at about 10 to 1 overall gearing at start. so with a 2.20 low that would work out to a 4.54 gear. but that may be too much gear for cruise.

I like the calculators at wallaceracing.com myself...

Sam
 

·
More for Less Racer
Joined
·
19,901 Posts
You're going to want a wide ratio if using a stock Muncie, which is something like 2.56:1 in 1st gear. It makes it much easier to take off from a stop compared to a close ratio of 2.20:1. Also makes it possible to not need deep 4.11 or 4.56 gear ratio in the rear axle.

If buying new you have the opportunity to get the 2.98 1st gear that AutoGear transmissions offers, that would be a much better choice and allow you to use a more cruise and mileage friendly 3.23 to 3.55 gear ratio in the rear axle.
 

·
Registered
Joined
·
4 Posts
Discussion Starter #4
Thanks for the help guys! Exactly the kind of help I was looking for. Much appreciated. Also, just on a side note, would the 327 bolt up to the straight axel with some motor mounts or do I need a new front suspension setup?
 

·
Registered
Joined
·
5,556 Posts
Your stock motor was front mounted so your 327 can be mounted the same.
How do you plan on mounting your trans? Side or rear mounted?
 

·
Registered
Joined
·
5,556 Posts
If you rear mount the tranny you need to side mount the motor. To much strain if the centre isn't supported better.
People do run them front/rear but I've heard it's not a good idea.
Other thing to consider with a 4 speed is shifter location. It'll be under the front edge of the seat.
 

·
Registered
Joined
·
1,132 Posts
I have a '64 vintage M20 wide ratio with the 2.56 1st gear and 3.89 rear in my car and I like it. The M20 after '65 became a 2.52 1st gear but essentially the same box. It takes off from a roll nicely and is good around town in traffic.


The thing is not to lug the engine down at lower speeds. My old rear was a 3.56 and the 3.89 lets me roll around corners in 3rd and not have to drop it back to 1st on 90 degree turns.
 

·
Registered
Joined
·
5,033 Posts
Thanks for the nod Eric!

To the OP: in a truck, you want around 9.5 - 10 for combined gear reduction (rear gear x 1st). So, like eric said, a 2.88 1st ST10 or a 2.98 1st "Muncie" with a 3.23 - 3.36 axle would be ideal.

Also mentioned, you need to pick one:
front engine mounts with the frame mounted bellhousing
side engine mounts with the 'floating' bellhousing and a crossmember

do NOT add a crossmember behind a frame mounted bellhousing. More often than not, you are asking for trouble.

Also know that a 32-spline muncie or T10 will require a little more homework to get the handle around the bench seat, and a shorter driveshaft than the earlier 27-spline output transmissions.
In addition, the diameter of the hole in the back of the bellhousing needs to be verified. There are 2 options, 4.685" and 5.125". Make sure your transmission has the correct "front bearing retainer" casting to match that hole. Replacement ones are available in either size.
 
1 - 9 of 9 Posts
Top