3.73 vs 3.08 rear gears - Hot Rod Forum : Hotrodders Bulletin Board
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Old 02-08-2007, 06:28 PM
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3.73 vs 3.08 rear gears

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

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Old 02-08-2007, 06:37 PM
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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
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Old 02-08-2007, 06:51 PM
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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.
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Old 02-08-2007, 06:55 PM
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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
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Old 02-08-2007, 07:06 PM
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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.
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Old 02-08-2007, 07:06 PM
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Still need more info. At what speed would you wan't to be running those rpm. Also are you running 235/60-15?'
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Old 02-08-2007, 07:14 PM
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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.
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Old 02-08-2007, 07:23 PM
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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.
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Old 02-09-2007, 12:23 AM
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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.
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Old 02-09-2007, 06:08 PM
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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
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Old 02-09-2007, 06:59 PM
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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.
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Old 02-09-2007, 07:05 PM
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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.........
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Old 02-09-2007, 07:49 PM
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if you dont want the 373s, just ship them to me
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Old 02-10-2007, 10:46 PM
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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.
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Old 02-12-2007, 11:59 AM
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Quote:
Originally Posted by 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.
62'-64' chevy nova also had drop out as long as it is 4-lug, 5 lug had spicer style
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