^Coulda sworn I had seen a 3.73 for these dang things....

 

Do you mean 4.10 or is it really 4.11

 

My dads truck as 3.92s and at 65 he runs about 2100 rpms. My truck which is exactly the same truck except mine has 3.55 gears. I run about 1750 or so at 65.

 

The RPM are also directly related to tire diameter. So if you increase your gear ratio by 1.104 and your tire size stays the same, your RPM would increase by a factor of 1.104 (the ratio 3.92/3.55).

So if you are now cruising at 70mph and 2000 RPM, you would be at about 2208 RPM at 70mph with the 3.92 gears.

On that same note, if you are producing 200 ft*lb of torque at 1500 RPM now, you will be producing about about 221 ft*lb of torque at 1500 RPM with the 3.92 gears.

I had the 3.92 gears put into my truck at the same time I upsized from 265/75R16s to 285/75R16s and don't recall seeing much difference. I cruise at a speedometer adjusted 70mph at almost exactly 2000 RPM now.

 

Well I've heard that with my truck being a 5 speed the 4.10s would hurt mileage more

 

There are no 3.73 gears for the 9.25 axle. Never made for that particular axle. If a truck ever came with them, Chrysler would, by law, have to at least a small inventory of them on hand for repair parts and there would at least be one aftermarket manufacturer offering them.

4.11 is the technically correct designation for Chrysler vehicles based on the 31 spline gear. 4.11 rotations of the pinion gear to one revolution of the ring gear. I only stress that for the newcomer who might only be able to find 4.11 gears in the parts catalogs, and worry that he might not be getting the correct gear set.

4.10 is a Chevy/Ford designation based on their spline count and actual gear size. And since their market share is significantly larger than the Mopar market share, 4.10 is used ubiquitously across all platforms. Even most gear vendors list them as 4.10s but you won't find that size in a corporate listing anywhere.

 

Also, there is really no difference. My '72 has FACTORY 4.10's out back, and FACTORY 4.11's up front. nothing to worry about. Your tires have more variance in size brand new then that.


Now that I think about it, the rear might be a 4.09.... can't remember for sure

 

Might be size of tire too, i run 2k rpms at about 76-77 mph according to the dash with 265 tires, and stock 3.55's.

According to my gps the speedometer is 3mph off tho, so it might actually be like 73-74