Log in

View Full Version : Picking a rear gear ratio

DRJDVM's '69
03-07-2010, 01:02 PM
Okay so I got my rear wheels and am about to order a rearend..

My tires are 27.75 diameter, and I'm planning on the T56 Magnum with 6th gear of 0.63.

I've done all the RPM calculators online, so I know what the RPM will be with diff set-ups.

My question is.....so what cruising RPM do you shoot for?

In my '69, with 3.73 and TKO 600, the motor starts to kinda lug if I go below 2k in 5th gear....but thats a carb car..

With the Barracuda, it will be a modern 6.1 HEMI, fuel injection etc etc.

I'm think a 4.10....and the 4.30 will be too steep and make 1st gear useless.... the 3.73 seems alittle low

4.10 at 70 MPH =2189
4.30 at 70 MPH= 2296
3.73 at 70 MPH= 1992
Payton King
03-07-2010, 03:10 PM
it is 285/19/35,stock C6 vette stuff. Anyway I am running a T56 out of a F body. I had a 3.80 and in 6th I was turning 1500 at 65. If anyone slowed me up it would start to buck. I changed it to a 4.10 and now I run 1750 at 65. Much,much better. I can still run 40-45 in 1st turning 7000. My gearing is perfect for me and my motor combo. My LS1 idles at 900.

Hope this helps.
ProdigyCustoms
03-07-2010, 04:22 PM
4.10 with that tire is perfect.
6spdcamaro
03-07-2010, 05:03 PM
it is 285/19/35,stock C6 vette stuff. Anyway I am running a T56 out of a F body. I had a 3.80 and in 6th I was turning 1500 at 65. If anyone slowed me up it would start to buck. I changed it to a 4.10 and now I run 1750 at 65. Much,much better. I can still run 40-45 in 1st turning 7000. My gearing is perfect for me and my motor combo. My LS1 idles at 900.

Hope this helps.

I think the old F-body 6 speed was a .50 6th gear though
rwhite692
03-21-2010, 08:41 PM
Looks like it has pretty much been answered already but I'd shoot for 65 MPH cruise right at 2K RPM. 4.10 should put you very close.

Of course you want to make sure your T56 1st gear is friendly to that 4.10, what is your T56's first gear ratio?
214Chevy
03-22-2010, 10:38 AM
I haven't driven mine yet, but I've talked to a million people (not literally) and they all said 4.10 with a 305/30/20 that is a 27" tall tire and my T56 Magnum. But hey, like I said, I haven't driven mine yet. So what in the hell do I know?:rofl: