demonpixel

iTrader: (19)

My setup is a TH400 with a 3000 stall, with 3.70 gears in the back. I'm still on stock 16" wheels. I was going to get 17" wheels but the deal fell through. Anyway, I can't drive this car on the highway at a speed I want to cruise at. I'm at 4000 rpm at 75-80mph so my temps creep up higher than I want them to.

I looked into the Gear Vendors od unit but it's a little pricey. A friend of mine has some Richmond 3.25 gears, but I don't know how much lower the rpms would be at cruise. I know there is this formula:

(mph x final gear ratio x 336)/tire height = rpm

and when I plug the numbers in:

(80mph x 3.25 x 336)/28 inch tire =

I get 3120 rpm.

That sounds pretty good. At 50mph, according to the formula, with 3.25 gears and a 28 inch tire, I get 1950 rpm.

BUT...I'm not sure how accurate this formula is to the real world.

I was wondering if there anyone out there that had a similar setup to mine and got their car to cruise decently. Thanks for any help/advice.

demonpixel

iTrader: (19)

I forgot to mention that I have a Ford 9". I found these 3:1 Motives on Summit: http://www.summitracing.com/parts/MGR-F890300/

They seem like a good highway cruising gearset.

They're for a 28 spline and my rearend is 31 spline. Will the 28 spline gears work in a 31 spline rearend without any problems?

Blue85350

iTrader: (1)

i have 3.23s and a 27" tire and cruise 80 at 3300 rpm. i used an online calculator (that has been right on mine so far) and got 3204 for your cruise speed. check out the calculator http://www.csgnetwork.com/multirpmcalc.html . if it helps i daily drive mine, and dont think its too bad.

quicksilver383

iTrader: (3)

As stated use an online calculator. Another consideration is your stall. Depending on it's efficiency you may cruise at a higher rpm than the calculator states and will vary depending on incline, headwind, ect.