What Rpm Is Ideal?

Anthonyb · April 3, 2010

I just put on 285/70/17 on my truck, 6.0 gasser with the Allison 6speed, and think I want to regear. I have 3.73's now and cannot decide on 4.11 or 4.56. Afraid of not enough of a difference or high reving engine on the hwy. Right now I am at about 1800 RPM's at 65mph. I was thinking 4.11 but the guy at the axle shop thinks 4.56 would be better. Anywhere between 45 and 65, it does a lot of down shifting. What is the ideal rpm at either 65 or 70mph to get good gas mileage and have good power. Any suggestions appreciated.

brims · April 4, 2010

The 3.23s against the 6 speed are equivalent to 4.10s against a 4 speed so going to 4.56 would be astronomical.

Matt_ · April 4, 2010

The 3.23s against the 6 speed are equivalent to 4.10s against a 4 speed so going to 4.56 would be astronomical.

depends on which gear you're talking about. and did you mean to say 3.42s? they're like having 4.56s in 1st gear w/the 4 speed. But the relationship changes for every gear.

6th gear in the 6spd is .67 as compared to .70 in the 4 speed... so with his 3.73s he's at a slight disadvantage as compared to the 4spd, and thus he's probably downshift to 5th to compensate.

To the OP... 4.10s would help but might not be worth gearing to since you already have 3.73s. And i think that the 4.56s coupled with the 6spd would be extreme overkill in the lower gears with the 6spd for that sized tire.

Do you have a tune? with the 6.0, 6spd and 3.73s you shouldnt have any trouble turning those tires @ 65mph without downshifting...

ATMINF · April 4, 2010

I would say get a tune and see what that does to wake things up. Also you have a 6L90 six speed trans, not the ALLY tranny. The 6L90 are supposed to be pretty strong also.

Big black truck · April 4, 2010

I agree, a tune will waken it up some and you can reprogram your shift pattern.

hockeypro1411 · April 4, 2010

In that picture it looks like your truck is bleeding some paint... Lol

Anthonyb · April 5, 2010

I ran the calcualtions and I think the 4.11 is the way to go. Thanks for the insight. I thought all of this time, my trans was the Alison and I thought my final drive was.70. I think the 4.56 is too low for the type of driving I do, mostly highway. I do have a programmer, the Edge CS and it made a huge difference. It firmed up the shifting and has increased the Torque substantially. I just want it to be even more responsive. I think I am being plagued by the Torque management system and that is what I am feeling. The Edge is supposed to adjust the TM system depending on the current conditions. I think getting back close to stock on gearing may also help gas mileage because of the bigger/heavier wheel and being a little higher in the powerband.

If she starts bleeding red or black, then I'll get concerned! lol.