turfquip

At 65 MPH, my engine is turning 2900 RPM's. That affects fuel mileage in a big way. I'd like to be turning around 2200 - 2400. Now here's the question:

My Rockwell rear axle is a 433. How big a job would it be to change it to a 355? Would axles need to be changed as well? I've got more than enough low end right now. I start the truck in 2nd from stop. First is low - low.

More importantly, would this change produce the desired RPM and fuel savings?

Thank You!

4x4

The 3.55 will help a lot, especially if you have overdrive. Unless you've done it before or are an extremely good mechanic you should have someone change them for you. The axle shafts will not need to be changed, and your mileage should increase dramatically. Good luck.

4x4

turfquip

Thanks,

I have a mechanic who is capable. There is no way I would even attempt it.

Do you believe I would see a reduction in RPM"s the way I hope to or maybe even better? No overdrive in this truck, it's a five speed.

Rare1

I guess that fifth gear is overdrive. Your owner's manual should have that info.

By ratio, your RPM with 3.55 gears at 65 MPH would be 2377. However, if you pull your 5er at its max safe speed stated in the manual, 55 MPH, your RPM with present gearing would be 2454. That would maintain the pulling power you now enjoy and also produce higher milage.

It's not only your RPM spoiling your milage, but also your speed. Between 2454 RPM and 2900 RPM there's no increase in torque but a large increase in horsepower produced. That increase in horsepower is needed to overcome the increased air resistance of pushing your rig at 65 instead of 55. Making more horsepower requires more fuel, but you knew that.

Have a look at this http://www.rversonline.org/fueleconomy.htm

Especially read the first sentence after the graph. I know this is not your or my rig in the study, but it does apply somewhat to all of us.