Need some help...quick!

mattie · May 29, 2004

Found a good deal to trade-in my '03' Crew Cab 6.0L gas for an '04' 2500 Avalanche with the 8.1L gas motor.

The only option I don't like on the Avalanche is that it has 4.10 gears. I asked about the dealer swaping for 3.73's and they said it's a 'huge' job.

Dealer claimed that, "you won't notice a heck of a lot of difference in mileage, etc, by having the 4.10's."

I probably drive 75% city.

Any opinions?????

Mattie

Roofer · May 29, 2004

You probably won't notice alot unless you are highway driving. 3.73's get better mileage just because of lower rpms. I wouldn't think that you would notice much difference. Besides, it's a big block, it's for power not mileage.

Mort · May 29, 2004

You do realize with 75% city driving you are only going to average 9 mpg with the 8.1 don't you?

snoman · May 30, 2004

Found a good deal to trade-in my '03' Crew Cab 6.0L gas for an '04' 2500 Avalanche with the 8.1L gas motor.

The only option I don't like on the Avalanche is that it has 4.10 gears. I asked about the dealer swaping for 3.73's and they said it's a 'huge' job.

Dealer claimed that, "you won't notice a heck of a lot of difference in mileage, etc, by having the 4.10's."

I probably drive 75% city.

Any opinions?????

Mattie

Why it the world would you not want 4.10 gears??? With overdrive your effective final drive is about 3 to 1 with a 4.10 ratio. That big heavy truck with the airodynamics of a brick will have marginal OD performance with 3.73 gears and mileage will be no better. If you ever plan to tow, you will be sorry if you get 3.73's. I have a 2000 K3500 with 4.10 gears and I am going to swap them out for 4.56's this year to get better OD performance when loaded.

mattie · May 30, 2004

Thanks everybody.

The 6.0L I've had since new has averaged 11.0 mpg according to the DIC....so I figure the 8.1L can't be much worse.

The 4.10's sound like the way to go.

Hey, really stupid extra question......I would assume that in the 8.1 Avalanche they would also use the Allison tranny, correct?

thanks again,

snoman · May 30, 2004

As far as I know GM uses only allison with 8.1 unless they just started using 4L85E with them. The 4L80/85E is up to the task but GM likes the markup on the Allison.

GlennRMK · May 30, 2004

If your doing mostly city driving I doubt you will notice a mileage difference. Actually, since 4.10s don't have to work the motor as hard to get you moving as 3.73s, the mileage, in the city might be slightly better.

Highway is the only place were you would notice, since your reving higher at a given speed.

I debated between 3.73s and 4.10s in my half ton. But opted for 3.73s because the speed limit is 75 MPH here in Montana, and I usually do 80-85 MPH, so my mileage would suffer with 4.10s.

HendyPhoto · May 30, 2004

Glenn, good point. I drive 75-80 on the freeway, and I am sure my 3.73 are giving me better mileage at those speeds. I dont do nearly as much city driving as I do freeway driving. I have no probs with the 3.73's towing or not. BUT I dont have anything with 4.10's to compare to, so i am happy.

snoman · May 30, 2004

If your doing mostly city driving I doubt you will notice a mileage difference. Actually, since 4.10s don't have to work the motor as hard to get you moving as 3.73s, the mileage, in the city might be slightly better.

Highway is the only place were you would notice, since your reving higher at a given speed.

I debated between 3.73s and 4.10s in my half ton. But opted for 3.73s because the speed limit is 75 MPH here in Montana, and I usually do 80-85 MPH, so my mileage would suffer with 4.10s.

I agree on the city mileage but disagree on the highway one. I remember have trucks with 4.1 without OD 20 to 30 years ago and doing 80 and better on highway. WIth a 3.73 and OD you will actuall work engine harder in OD at speed (engine torque needed to move vehical) than with 4.10. a 3000 RPM or better cruise at 85 or so is not a problem nore hurting fuel mileage as gasser run more efficently at higher RPM than diesels do and use less gas when running is that "range" The presence of OD complete changes to axle ratio equations for cruising. BTW I lived in Montana for a spell and you should alway select a deeper ratio at higher altitudes and for frequent hill climbs on highway. I have 3.73 in a 89 4x4 suburban and it piulls OD well up to 4000 ft or so but above 6000 ft it really starts to lack and at 8000 ft is it basically unuseable. A 4.1 ratio would help if I still lived out in the rockies throught I still travel out there from time to time.