Thinking about a gear swap in the near future, but do not want to send my mileage plummeting. Most of my driving is a long (40 mile) commute with the morning half being around 70 mph most of the way and the way home usually is about evenly split between stop and go and clear freeway.

I have read that some with a 2wd 5.3 and 3.73's get about the same mileage that I do now (19-20 mpg), and was hoping to get a few more responses. I'm hoping that a 10% increase in engine revolutions does not directly translate into 10% more fuel consumed. There are obviously many more variables, but in general what is the effect on highway mileage from a gear swap such as this? Also would a good cat-back, CAI and tune be able to make up for any potential losses?

The 3.23's seep to be pretty conservative for such a heavy truck, not sure why the factory didn't start with at least 3.42's.

Thanks.

 

i can tell you this. when you get the 3.73's, you'd wish you'd went with 4.10's. i went from 3.42's to 4.10's and i still get 20mpg on the hwy.

 

Thats right I went with 3.90s from 3.42 and it never hurt my mileage now that I put on the Radix S/C im now getting 22+mpg.

 

i can pull 23mpg on freeway @ 65mph.

 

The key to mileage with our motors is RPM's. If I had it to do over again I would have stayed with my 3.73's instead of going to 4.10's, for two reasons:

1) With 4.10's I lost 2+ MPG on the freeway
2) After 20-25 mph or so the 4.10's have zero benefit.

As far as I am concerned, 3.73's are the ideal highway gear for trucks with 31-32 inch tires. At 70-75 MPH you are crusing at 2000 RPM or so which is still within the sweet spot as far as gas mileage for our motors (1800-2000 RPM). The further you go over 2000 RPM, your mileage starts to dive.

I agree with you that 3.23 are ridiculous for a big-*** crew cab truck. I bet 3.73's will serve you just fine, and with all of your time on the freeway, with mileage a concern, they are likely a perfect fit.

 

With 3.73's and 30.5" tires and 4.10's with 30.5" tires I averaged 14something mpg's with both all day everyday.

With 4.10's and 32" tires and a Radix I average 12mpg's with a "highway only" best of 17mpg's at 75mph cruising.

 

From the performance aspect of this, the 3.73 gears are the way to go.
To keep your miliage about the same on HWY, keep the RPM's at 1900.
That will get you to about 67 MPH. You can run 70 MPH with little loss in MPG.
After 2000 RPM's the engine starts going into it's power band and of course your miliage will suffer.
At 65 MPH you should get about 18 MPG w/ 3.73's.
You want gas miliage or better performance? That's what your going to have to ask yourself.

Jim

 

Thanks for the input guys. I knew that there would be some trade-off, but wanted to see how big the payment would be for the extra performance.

If I had an RCSB that I was planning on taking to the track often, I'd probably consider the 4.10's seriously, but this is going to be my commuter/long trip vehicle, so 3.73's sounded like a good compromise.

Mods: Thanks for moving to the drivetrain forum, I didn't know whether this was primarily a mileage (and thus general) topic or a gear topic. I just don't want to be thought of as the guy that doesn't know how to use a message board.

 

yeah I would go with 3:23's as well,,, I dont remember seeing you around the site, but welcome aboard anyways... hey what part of houston are you from???

 

No problem, don't get to many thank you's around here so here's to ya