2.72 rear end !!HELP!!
Thread Starter
Instructor
Joined: Feb 2004
Posts: 124
Likes: 0
From: Brighton Colorado
2.72 rear end !!HELP!!
I have a 81' vette with the 2.72 gears in the rear, i was thinking of changing to a 3.08 or a 3.30 something (not sure whats available for vettes) but it has independent rear so would it be hard? And would i notice much of a diff between a 2.72 and a 3.30 or so, and how much would that effect my millage? :chevy
Le Mans Master
Joined: Jun 2002
Posts: 8,339
Likes: 24
From: I can walk to MA
Re: 2.72 rear end !!HELP!! (allancook5)
Not too bad of a job to pull the rear end out, but not so easy, either.
You'll probably come across a few areas that need attention or upgrades
like adjustable strut rods/etc.
The torque increase will be 3.3/2.72 = 1.21 ... 21% increase in torque.
The mileage will go 2.72/3.3=.82 ... mileage drops by 18%.
:seeya
You'll probably come across a few areas that need attention or upgrades
like adjustable strut rods/etc.
The torque increase will be 3.3/2.72 = 1.21 ... 21% increase in torque.
The mileage will go 2.72/3.3=.82 ... mileage drops by 18%.
:seeya
Race Director
Joined: Jan 2003
Posts: 15,177
Likes: 90
From: State of Confusion
Re: 2.72 rear end !!HELP!! (NHvette)
The torque increase will be 3.3/2.72 = 1.21 ... 21% increase in torque.
The mileage will go 2.72/3.3=.82 ... mileage drops by 18%.
The mileage will go 2.72/3.3=.82 ... mileage drops by 18%.
My bone-stock '82, with less than 22,000 miles, got 23+ MPG on a 230-mile, all-highway trip with the original 2.87 gears;
last Fall, after a swap to 3.73s, I took 2 decent rides, totalling 430+ miles, with less than 175 miles being highway, and without even trying to get good mileage (several back-roads & turn-arounds; A/C blowing ice-cubes; stop-n-go city streets), I got 17+ MPG.
I'm ' guessing ' if the gearing is TOO-TALL (2.72:1, 2.56:1, 2.29:1, etc.), the motor is kept below the most-effecient operating RPM, and mileage could actually suffer...
:confused:
A few buddies with hot street/strip cars, that are rarely/never driven on the highways (i.e.: city-driving exclusively) say that going from 3.55s/3.73s to 4.11s had little-to-no effect on MPG-figures.
[Modified by Glensgages, 11:30 AM 3/3/2004]
Tech Contributor
Joined: Aug 1999
Posts: 15,195
Likes: 4,024
From: Connecticut, USA
Re: 2.72 rear end !!HELP!! (NHvette)
Interesting, I'm going to be setting up a differential for a friend and he's swapping the 336's for 273's. Running a 2.64:1 ST-10 4 spd, he wants lower highway cruise RPM over accelertion.
Gary
Gary
Race Director
Joined: Jan 2003
Posts: 15,177
Likes: 90
From: State of Confusion
Re: 2.72 rear end !!HELP!! (NHvette)
You're right - the 18% drop would be cruising highway speed in top gear.
Either an 18% slower MPH at a given RPM, or 18% more RPM to turn a given MPH
Acceleration is improved, so round-town driving may be much better.
I used to drive around-town and down back-roads in 3rd gear (of the 700R4) to keep the R's up;
but with the .73s, it is much better!!!
:thumbs:
Instructor
Joined: Jan 2004
Posts: 246
Likes: 0
From: Marshalltown Iowa
Re: 2.72 rear end !!HELP!! (allancook5)
Just got done with my '81. I am sure you will find plenty of help here if you get stuck. I must admit that setting up the carrier preload is a treat you will remember for life since the shims are located BEHIND the bearings! :banghead: :banghead: :banghead:
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Le Mans Master
Joined: Mar 2002
Posts: 7,456
Likes: 2
From: Coming home from Luckenbach Texas
Re: 2.72 rear end !!HELP!! (allancook5)
Stick a 700R4 transmission in there. It has a low 1st gear that'll launch the car...and overdrive for some sweet freeway cruising!
Le Mans Master
Joined: Apr 2001
Posts: 5,000
Likes: 1
From: Minneapolis, Mn USA
Re: 2.72 rear end !!HELP!! (page62)
Stick a 700R4 transmission in there. It has a low 1st gear that'll launch the car...and overdrive for some sweet freeway cruising!
Youll get way more bang for your buck if you go 700R4 or 200R4 instead of rear gears since the first gear is much lower and you'll get the OD 4th gear lock-up feature which will give you great mileage and improved acceleration.
Bowtieoverdrives.com or 700R4.com has a kit just for the C3s.
Brent...
