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MG TD TF 1500 - Final Drive Ratio verses RPMs

Is there a chart that tells what RPMs equals speed with each rear ratio? In other words, approximately 3600 RPMs give me 55 MPH with a 4.8 final drive. I would like to know how that would work out with a 4.3 and also a 4.1 rear. Anyone have these specs? My 1500 rebuilt engine has very little hours on it and is in top condition, plenty of power for a stock engine, so that's of no concern, the ratio verses RPMs is what I would like to know. I know tire size plays into this a bit, so approximations are ok. Thanks. PJ
Paul161

Yeah Paul. You need to get the Carl Cederstarand booklet. Get in touch with Bud & he'll email you a copy. The 4.3 is as tall as you need to go. Cheers
Peter TD 5801
P Hehir

Here's one Paul

http://www.ttalk.info/RearGearInfo.html
MG LaVerne

Paul, see http://www.ttalk.info/RearEndConversion.htm for a link to the Cederstrand info. Bud
Bud Krueger

Thanks LaVerne, Looks like a 4.3 should be pretty close to where I want to be. PJ



Paul161

Bud, Thanks for the Cederstrand information. I down loaded it. We were posting at the same time. PJ
Paul161

3600rpm, 4.875 diff, 55 mph.
3600rpm, 4.3 diff, 62.4 mph.
3600rpm, 4.1 diff, 65.4 mph.
R A WILSON

Forgot to say, with a 1500 engine I'd go for the 4.1 diff. My engine is 1380cc with a 4.3 diff, but I think a 4.1 would be better. Don't forget to recalibrate your speedometer.
R A WILSON

More input on the 4.1. We have a fellow in our local T club who uses 4.1 in his 1500 TF. He also happens to be a instructor at the Bondurrant school of high performance driving. Drives the car to work. Only drawback to 4.1 seems to be running in third when on local streets but runs great on the Interstate.

When Dave Clark and I talked when he was wintering down here, he told me he had sold a 4.1 and 3.9 to AU. They do a lot of highway cruising with the MG club and the guy wanted to be able to run with the MGBs on trips.

So it depends where you are headed -- highway vs local street use.

Joe
JWP Policastro

Keep in mind that tire size is a factor. You can better or worsen your setup simply by moving to a taller or shorter tire.

Rotations per mile and all that....

24" tall tire will turn 877 revs/mile x 4.3 = 3771 at the crank. 877 x 4.1 = 3596 at the crank.

26" tall tire will turn 807 revs/mile x 4.3 = 3470 at the crank. 807 x 4.1 = 3308 at the crank.

24"/4.3 = 3771
26"/4.1 = 3308

463 rpm difference/mile is a lot. Measure your tires, boys.

For the heck of it: 25"/4.8(original) = 4032

(I hope my math is right)
.....

MAndrus

One of the conversion tables takes into consideration the form and size of the tire. Anybody happen to know its URL? Bud
Bud Krueger

See http://www.currieenterprises.com/cestore/calculators.aspx#? for a whole bunch of info. Bud
Bud Krueger

The chart that was put on the site by me and Steve Blomberg also has tire size stuff to determine speed. I have the 4.1 in my TD bored 80 over and I run 3500-4000 or so and keep up with traffic easily with no real strain on the engine.
TRM Maine

This thread was discussed between 29/08/2015 and 30/08/2015

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