Ideal rearend ratio????????

[Richard Calhoun]

347 stroked, tremac trany, 430 HP. 17" wheels. What's best??
3:27, 3:55, or 3:73 ???

Opinions please.

Thanks

Richard

[Frank Coppola]

I am no expert on ratios but I will tell you this: I have a 3:50 rear with a C-6 3 speed. At 70 mph I'm running about 3,500 rpm +/- 300. If I had a lower ratio I would probably kill myself as there is no end to the pedal. The fun of driving personally speaking is coming off the line. Doing 160mph in a Cobra with a fiberglass body, no airbags, and manual brakes is an unneccesary risk.

My answer to you is to tailor your ratio to what kind of driving you're going to do. I'm sure there is a way to calucate your RPM's vs. MPH with the tranny and wheels you have, but I can't help you there.

[renaissance man]

I would have to agree Frank.

I'm no expert either but I'm running a 289 HiPo, 17" wheels and a 4.10 rearend with a 4-Speed Toploader. About 4k rpm at 70 but that's my peak torque from 4000-4500. I just mash on the gas and I'm gone! No down-shifting! But I don't care to do 150mph. I like the off-the-line response not to mention the car sounds like a Nascar winding out!

[Back in Black]

My transmission slated for my West Coast is the Richmond Over Drive (ROD) 6 speed, low first, and way overdrive 6th.

17 inch wheels, low profile z rated Michelins

The WCC's are easily 500+ lbs heavier than your car, and I think this will be fine, since I have a 600+ horsepower motor planned...I suggest strongly the 3.27 gears, or you will be doing the kind of excessive rpms the guys just mentioned. Your cobra is light, and has plenty of pickup with the higher ratio....I want to use 5th gear if needed, on the highway, rather than go to taller gears and use 6th...there is a great advantage to the 6 speed, if you don't mind shifting more often (part of the fun for me)

More gears are better!

Bigger is better!!

[flipper35]

I agree with Back in Black, mine runs about 2000 at 70mph and still runs low 12's in the quarter. But if you do track time and not much highway time, you may want to go shorter.

[Shell Valley]

www.richmondgear.com

They have a calculator there that tells you what gear you should run for a desired rpm. IE - you tell it you want to turn 3000 rpm @ 70 mph and put in tire diameter and it tells you what gear to run.

I've used it a few times to figure out which gears to run at different dirt tracks for my stock car and it seems to be fairly accurate.

Hope this helps!
-Dana

[Dominik]

hi,

in europe the magazines (and we) clocked from 0 to 62 mph, 0 to 100 mph and 0 to 124 mph (that equals 100 kph, 160 kph and 200 kph).

therefore I geared my car to give me 62 (plus) in 1st gear (2.20:1), 100 in 2nd (1.64:1) and 124 in 3rd (1.34:1) - or something! that resulted in a Muncie M-22 or T-10 CR trans with 275-60-15 tires at 6600 RPM (3.31:1 rear).

for the US I would use a WR trans (4-speed) that you can go quick from the traffic light and cruise easy at 65 mph.

If you are racing check for the maximum speed you can achieve at the longest straight. (probably not more than 140 mph)

dominik

[webebob]

If you are wanting certain drag times, say, 120mph in the quarter, make sure your gearing doesn't require an unneccessary shift at 112mph, or something along those lines. Or worse yet 118mph!
Bob

[acaskie]

I have a Tremec with a .68 overdrive fifth. Originally the rear was a 3:31, and fifth gear was virtually useless unless the speed was 75+ MPH.

I thought about going to a 3:73, but worried that with a first gear ratio of 3:27, first gear would be too short. Eventually I went to a 3:54 rear, and that has been satisfactory, although still not ideal. At least fifth is more useable now, and I can get into fourth around town.

Tremec makes a replacement cog for fifth at .82. That combined with the 3:54 rear might be the best combo. If more punch off the line is your goal, then go with the 3:73 and leave fifth alone. just don't be surprised if you have to shift out of first at around 40 MPH. good luck - - Allen