Hi all,
I am thinking of removing my 3:73 gears and going to 3:31 to make the car a little more highway friendy, Is anyone running 3:31's in the rear and what are you taching at 75mph? I run a 27" tall tire in the rear (255 60's). Right now I taching around 3600 rpm to run 75. I would like to see it down arount 3100 - 3200 rpm at 75mph. Is anyone running this combo?
Thanks in advance

Your car will be a dog off the line with 3:31 gears.

I ran a 3.31 in a '72 SS454 4 speed Chevelle and a '67 SS396 Powerglide Chevelle. They both ran well with the 3.31s and were easy to drive on the highway. You do know that there are no new 3.31 gears don't you? You will have to find a good used set.

I have 3:31 gears and with 215x15x65 I run exactly half... 60mph is 3000 rpm, 70mph is 3500 rpm. with an m21 stock geared 4 speed

OK, I ordered my car with the stock, (unchecked "rearend gear ratio" line on the order form), gears which are the 3.31's!

25.3" to 25.5" tall tire is right at 3050 to 3070 rpm at 70 mph!!

I love my 3.31's and I wished somebody would re-pop them b/c you can turn a tire as well as go down the hwy fine, imho!!

pdq67

Back then stock 350SS, M-20, 3.31's and D-70/14 Redlines.......

Thanks for the quik replys.
I parted out a 69 big block impala years ago and still have the 12 bolt rear end. The gears look real good and was thinking about swaping them for my 3:73s. I know it will be a bit soggy out of hole but it sounds like the drop in rpms at 75 will make it worth the swap.
Thanks

I had a set of 3.31's with a BBC 4spd chevelle and they weren't that soggy. You will like them.

What cam are you running? Also, from your sig, I'm assuming you're running a 4-speed,..is it wide or close ratio box?

And,..don't forget, most our cars new were equipped with tires 24-25" tall on 14" wheels. So factory 3.31 gearing with a 27" tire will behave like a 3.08 geared car, comparitively speaking (diff between Pi of 25" vs 27" = 92.5% ).

Straight line,
I am running a Repo Crane version of the 375 Horse 396 solid. The 4 speed is a wide ratio box.
Thanks Again

A friend of mine has a '69 Chevelle SS with a 461 BB, M21, and 3.31 rear. He's running 295/50-15's on the back. It pulls out pretty well, but the torque of the engine helps a lot. I'm trying to talk him into putting a TKO 600 road race tranny in the car. Final drive in first gear will be about 9.50:1 and fifth will be 2.71:1. I think this would make one fine street machine with this combo.

That was a pretty healthy cam,..a solid with 242 degree duration @ .50

According to my book, 3.31 is listed as an "economy" gear for the L-78 and L-89 cars,..which again, came with 14" wheels and 25" tall tires.

Std rear gear for L-78 and L-89 was the 3.55 which is effectively what you're running (or even less numerically) with the 3.73's and taller tires.

I don't think you'll like the 3.31's and tall tires with that cam which doesn't have much below 2000 rpm.

My opinion.

Your right, the car dosn't like to be idled around. maybe I should start looking into a 5 speed or a gear vendors overdrive so I can go down the highway a little easier. I do still like to go to the track a few times a year and want the car to stay in the 12's.
Thanks Again

maybe I should start looking into a 5 speed or a gear vendors overdrive so I can go down the highway a little easier. I do still like to go to the track a few times a year and want the car to stay in the 12's.
Thanks Again

If you can swing it and dont care that the car has to have a muncie in it the 5 speed is the way to go. A Tremec 5 speed with your current setup at 75mph in 5th gear youd be running about 2400 rpms.

4SPEED68
The 3.31s should be perfect for what you want, IMO.
I had a 67 RS with a 9 to 1 408 BBC (Lingenfelter did the flow work on the cast iron intake and heads), a M21, and 275-60-15 Eagles.
It would run consitent 12.900s to 12.950s (without breaking parts) and could be cruised anywhere.
Eric

Why not 3:42s??

thorpe67rs
Wow!! that Tremec does sould like just what I need. If I can keep my current gear and run 75 at 2400 That would far exceed what I could hope for. Can I ask what a set up like yours ran? How does it shift compared to the Muncie? Will it take the beating of the et streets on a sticky track?

L72/RS
That is good to hear. I am kinda at the bubble right now 12.81 @108 is my best but the car generally runs 12.85 - 12.90. I am at 5500'

peacock71
The reason for the 3:31s is I already have them

The Tremec TKO 600 is rated for up to 600HP. I bought the kit from ClassicChevy5speed. I had a muncie in mine as well prior to the switch. The kit was $2700 and includes the tranny, crossmember, driveshaft, shifter, (Tremec shifter) and speedo cable. Basically all i had to get beyond that was a new 26 spline clutch disk for $80. The first four gears will run pretty close to what you have with the muncie but of course with that sweet 5th gear for cruisin. Ive only put about 8 miles on my car since i put mine in and i can already tell you its awesome. Here is Classic Chevys site which has a bunch of great info and an rpm calculator you can play around with.
http://classicchevy5speed.com/

thorp67RS

Thanks for the info!!! That is exactly what I am going to do. Just need to do a little extra side work as I dont want to light the visa card on fire LOL...
I,m sold.
Thanks Again

Your welcome. Jim (GMJim) and Jeff at classic chevy are great guys and regulars on this site. They are always available to answer your questions. Good luck. PS...i guess youll have to change your screen name. :D

The TKO600 is available with two different fifth gear ratios. If you're going to run 3.31's in the rear the .82 will give you 2.71 final drive and the .64 will give 2.12 which might be too high.

I have 3.31's in my Nova and it is also equipped with the Tremec 5 speed. The steep 1st gear and the tall 5th gear give me the best of both worlds. I have a mild Crane cam in it and the engine is rarely revved over 5K rpm. The rpm's at cruise were reduced by 800 in 5th and it runs right at 2K while motoring down the highway at 65mph. If you need to pass quickly, knock it down a gear or two and away you go. If you decide to go with the Tremec the big differences you will notice are the increased gas mileage and reduced cabin noise, not to mention wear and tear on your engine. Matter of fact I was so pleased with the Tremec in my Nova I put one in my 68 Z28 as well.