Gearing

[Smokey73]

We've got a 379ex pete that we're wanting to retire from the road and start pulling a camper with. We want to remove the front driver and move the fifth wheel back. It's running a 550 hp C-16 and an 18 spd w/3.55's. What gearing could we go to for mileage? The camper we've got now wieghs in at about 18k, and the truck won't ever see anything over that.

 

[Freightrain]

It likely won't ever get anything worse then when bobtailing now, or if it pulled an empty flat. Do they even offer any lighter gearing that would make any difference?

 

[Smokey73]

I'm not sure about the higher gearing, that's what I was wondering. Right now, with the old man driving, I think he gets about 7.5 or 8 average. He's wanting to know if there are higher gearing options maybe 3.08 or something in that range

 

[PackRat]

Calculate your gearing based on your intended travel speed. Shoot for 1200-1400 rpm. I'd suggest 1300 @ 75mph in high gear. It gives you pedal if you want to go stepping, and you can always run in 16 or 17 on slower roads. The last trucks I was involved with @ K-W were ordered with 3.36's, but Pete was pushing 3.26's(with a 475hp C15+18-speed autoshift on 11r24.5 tires).
Actually, unless you need the wheelbase, you might consider removing the rear suspension, and moving the rear axle forward. It will maneuver much better.

 

[ameristar1]

They do have 3.08s out there and some 2.93, 2.79s (possibly?), but with that big power combo and no weight that Cat will be loafing along. PackRat is right about getting rid of one of the axles; less drag and weight, help the mpg. Remap the computer and probably pick up another .5 to 1 mpg. Just don't blow past people at 140 mph at night!