T5 and IRS Final Drive Gearing

[hayton55]

Was wondering guys, what is the rpm's when you hit 5th around 60 mph? I'm seeing only around 17 or 18 hundred rpms, engine kind of lugs at that low of an rpm…..

[jceckard]

Try using an online calculator like:

http://www.tremec.com/calculadora.php

You'll need to know your rear end gear ratio, the diameter of the tires, and the ratio of the gears in the transmission (if your's isn't in the list).

[hayton55]

Thanks, I should have researched the forum first before asking the question. It appears that this rpm in 5th is somewhat normal; didn't know enough at the time of purchase to ask for a higher gear ratio so that I could use the 5th gear without fear of a speeding ticket…..

[jceckard]

No worries. Happy to help. I'm one of the "living vicariously through others." It's not often I get to chime in with useful info. One of these days I'm going to join the ranks. Just waiting for my mid-life crisis to kick into full gear.

[rich grsc]

A T-5 with 3:55 gears, 1800 rpm gives me about 55 mph. Have a 331 with stack EFI, have dropped all the way down to 1400 rpm in 5th. No lugging bucking or stumbles, just a clean steady pull back to speed.

[DaveS53]

There are many online calculators to give you the exact speed, with any rpm, gear ratio and tire diameter. My car runs 2000 rpm at 75 mph or 1600 at 60 mph. A 430 hp LS3 has a mild cam and no problem cruising at low engine speeds. I had that all figured out before buying the rear end gears. If you want to accelerate briskly, downshift first. Overdrive gears are for highway cruising.

http://www.wallaceracing.com/calc-gear-tire-rpm-mph.php