I have 3:55 gears and want to change to a taller gear. How can i figure out the affect it will have on my rpm verses the different ratios. I am leaning towards a 3:73 for fear of tacking up the motor and killing my gas mileage and I am doing this to help when towing my boat. One person says a 3:73 will do all I need and somebody else says go with the 4:10. I am not gonna drag race or anything but I just want more torque for going up hills and inclines. Keep in my I do alot of interstate travel with and without the boat. Thanks for any help.
Mike

 

Welcome !! You can tinker with rear end ratios, tire heights, and RPMs in each gear here. The 4R70W ratios are: 2.84/1.55/1/.7 to 1.

www.ring-pinion.com/calculators.html

 

Seagasim,
The 383's are only 5% taller then what you have now and you probably will not realize much of a seat of the pants difference. Most are dissapointed when putting out the kind of money a gear change will require and only getting 5% improvement in performance. 4.10's will be more like a 15% improvement. I went with the 4.30's but I don't drive much on the highway except when towing. If you have read my posts you will see I have actually been getting better milage then with the 3.55's. That is for combined, mostly back road driving.

 

A great calculator here:

http://www.smokemup.com/utilities/calc/mph_range2.cfm

 

To quickly calculate your rpm change after replacing your ring & pinion, use the following formula;

current rpm @ known speed X (new ratio / existing ratio)

Lets say that you now turn 2500 rpm @ 60 mph.

therefore;

2500 x (3.73 / 3.55) = 2500 x (1.0507) = 2627 rpm.

Since the number in brackets will stay the same for that gear ratio change, you can store it in the memory of your calculator and apply it to any rpm that you curently run at to see what your new rpm will be. Have fun, GlennMc.