[cares]

I'm looking to get higher gears in my '57 Chevy for cruising. Will I get
better gas mileage with the 3.08's? And will it be worth the effort to
make the change over?
Thanks

 

[bates_k]

You need to decide what sized tires that you're going to use,
then what rpm you're going to be comfortable running, to choose
the rear gear ratio...

K

 

[poncho62]

There are a few factors to consider,.........What tranny (1:1, OD).....Tire size......comfortable RPM range........etc

The 55-64 Chevy rears had a 3.34 ratio also....I always found it just about perfect.

 

[cares]

I currently have 235x15's on the Chevy. It has a Muncie 4 spd and I would
like to run around 2200-2500 rpms.
thanks for the information

 

[yknot]

Your also forgeting the main input here the engine....how much HP does it have and what is the torque?? Usually a good RPM is the PRM that makes just under max torque.

 

[red_rider52]

Still need more info. At what speed would you wan't to be running those rpm. Also are you running 235/60-15?'

 

[1957plymouthhemi]

All the questions asked are very valid for what your trying to do. There are numerious calculators available on line to determine cruising RPM at a specific MPH and tire size and gear ratio.

In generalities the 3.08 will make a siginificant difference for highway cruising, with the trade off being around town type acceleration. If you are running a lumpy cam, the 3.08 make it a little less friendly at lower RPM such as in city cruising.

The best of both worlds is usually a relatively deep rear end gear and OD set up.

 

[xntrik]

Here try this // The 5 speed result doesn't compute but the rest seems OK.

You can take your direct gear rpm x your OD ratio, yourself at the bottom.

http://www.csgnetwork.com/multirpmcalc.html

or Google for more info.

 

[jimfulco]

I changed a '72 Nova from 3.42 to 3.08, and highway mileage increased from 15 to 17. This was with a stock engine. Later engine mods got the highway mileage up to 21 or so.

I went from 2.73 to 3.45 in an '88 T-bird, and highway gas mileage went from 26 to 22. City mileage didn't change to amount to anything, and the fun factor went way up.

 

[cares]

Thanks for the information...I going to go with the 3.08's... Now, where is
a good dealer with reputable gears? I don't need posi...
Thanks

 

[tab]

Gas is going to go back up again. The 3.08 is fine. If you have to race, just go from the roll.

I had a hot rod 72, Formula Firbird with a 273. I loved it. I raced a Ferrari on the highway once. What a hoot.

 

[poncho62]

The nice thing about a 57 (55-64) Chevy rear, is that you can have extra pots with different gears, that can be changed in an hour or so.........

 

[steve t]

if you dont want the 373s, just ship them to me

 

[jimfulco]

You also need to consider your final gear ratio in low gear. It's going to take some heavy clutch-slipping to get it moving from a dead stop with 3.08's and a Muncie.

When I changed my Nova to 3.08's, it was real uncomfortable crossing a busy highway from a stop sign, so much so that I ended up swapping the original trans, which had a 2.54:1 low gear, to one with a 3.11 low gear. That's in a 3200# car with a nearly stock 350 and a heavy flywheel. If your Muncie's an M-21 or M-22, with the 2.20 low gear, it will be even worse.

Might be worth the trouble to see if you can find a used center section with 3.08 gears already in it, and stick it in your housing just to see how you like it. '55-'64 Chevy cars & '55-'62 Corvettes use the same center section.

 

[60pontiacdude]

You also need to consider your final gear ratio in low gear. It's going to take some heavy clutch-slipping to get it moving from a dead stop with 3.08's and a Muncie.

When I changed my Nova to 3.08's, it was real uncomfortable crossing a busy highway from a stop sign, so much so that I ended up swapping the original trans, which had a 2.54:1 low gear, to one with a 3.11 low gear. That's in a 3200# car with a nearly stock 350 and a heavy flywheel. If your Muncie's an M-21 or M-22, with the 2.20 low gear, it will be even worse.

Might be worth the trouble to see if you can find a used center section with 3.08 gears already in it, and stick it in your housing just to see how you like it. '55-'64 Chevy cars & '55-'62 Corvettes use the same center section.

62'-64' chevy nova also had drop out as long as it is 4-lug, 5 lug had spicer style

 

[xntrik]

My buddy went from 355 to 293 in his 383 eng AT and gained 1.5 mpg on a 700 mile trip last weekend. Got it up to 12 he said.