PDA

View Full Version : diesel gearing


78bronco
10-07-2007, 01:52 PM
ok so I put 39.5 on my truck and now it feels gutless so I did some math and figured out that I should have 4.33 gears to make it work as if it had stock size tires! but everwhere I read people say not to do this. so whats the thought on this??:dontknow:

Nutbar
10-07-2007, 02:00 PM
Did you like the way it was geared stock . . . if you want a little more pullin power (not that you usually need it with a deisel) gear it a little bit lower (higher numerically) but just remember that deisels have a very small power band and if you gear them too low they have no highway driveabillity.

Most of the guys I know runnin Cummins Dodges usually wind up runnin with around 3.55 gears with 32-33 in tires.

78bronco
10-07-2007, 02:52 PM
and I got 39.5 and I loved the way it pulled when it had 33's on it and I was looking at 4.30's but I cant find any for a dana 70[j]

tenpack
10-07-2007, 09:05 PM
nutbar hit it on the nose. 410s on a truck are great for towing but highway revs are too high, but they get the load moving easier. say 355s take more grunt to get the load moving, but lower rpms make for better fuel economy.

Air on the higher(numerically lower) side, can always juice the engine more.

kootenaycat
10-07-2007, 09:44 PM
nutbar hit it on the nose. 410s on a truck are great for towing but highway revs are too high, but they get the load moving easier. say 355s take more grunt to get the load moving, but lower rpms make for better fuel economy.

Air on the higher(numerically lower) side, can always juice the engine more.

Think he must have had 3.55's with 33's, cause he was happy with them. But 39.5's will require 4.27's roughly to have the same power.

http://www.superlift.com/library/gears.asp

I'd go with either 4.10's or better (higher numerically) if you want the same pulling power. Unless you're always doing 70mph or better on the freeway, I'd go with 4.88's rather then the 4.10's. If you're a speed demon and doing 80mph or better on a regular basis, go with 4.10's.

78bronco
10-08-2007, 01:51 AM
I did the math and it seems I need a 4.37 gear ratio so I went looking for 4.33's and found them for the dana 60 front but I cant find any for a dana 70 rear:( but they make 4.33 for a dana 80:dontknow: and I think that 4.88's are way to high but your hit it on the nose with that kootenycat

Punk in Drublic
10-10-2007, 12:17 PM
4.56 :dontknow:

ottoman
10-10-2007, 11:05 PM
try some 410's they are pretty close and easy to find for any diff