Truck gearing opinion

Does it go the speed limit in all states you drive in?? ................................................There's your answer unless you have money to spare more on fuel.

 

ohhhhh now your getting clearer as to why. Makes sense now. I have no clue being I don't haul that stuff. GL and sure your answers coming soon. Stay Safe!!

 

3.55 to 3.70 isn't a noticeable difference, I went from the other way due to a rear end failure and had the 3.55's already. If the 10 speed you are using is an Eaton and starts with RTX on model number it and the 13 will both be final .73 ratio. Wouldn't have to calibrate speed and would have that half gear in every hole to help with down shifts. If the 10 speed is an rto then it still an overdrive but could only be .80 or there about which means the 13 would be taller and if its an RT that means direct final ratio which would be a jump. All in all I would say trans would help some but I would get with a good transmission shop and have them go over the ratios with you to see whats best.

 

A 3.7 would slow it down and require more rpm to go the same speed.

Many dont understand rear ends and I hope you do...but encase you dont......

Rear ends and tire size should be speced to have your rpm in the engines max mpg while at cruise. Putting in a higher rear end number will give you a lower 1st gear. You could also get a 13 speed with a "low" gear to compensate and not change your rear. Assuming you have an over drive trans, the rear end is fine. If you want more off the line power, a 13 speed trans would help. Changing the rear end wont help with power in the mid gears, because all it will do is change your shift speeds, not your rpm or power.

Now, If i'm not mistakin, that engine cant do 500 horse stock although can be reprogrammed to do it. The main thing you need to torqe. Se if whoever works on your motor can increase your torque. That would help you off the line and accelerate faster. ofcourse if you use your right foot, you will have better proformance but may loose mpg if your to aggressive he foot.

So to clairify, if you can get more power out of the motor do that...maybe switch to a 13 speed, but dont change the rear.

 

I would leave it alone. 355 ratio is good for most terrain. You have decent pulling power and fuel mileage. If you want to change anything, you could go with a 13 speed transmission, but if it were me, I would not spend the money. I don't think it will do much to help you.

 

A non overdrive transmission will be the most duel efficient move. However.....to do this you will need to change your rear end ratio in the opposite direction that you are speaking of. Let's see.......is there a 3.08 available for truck rear ends? 3.08 + non overdrive transmission = maximum efficiency.

 

The 3.55s are fine. It's a good overall gear ratio to have unless you're pulling really wide or really heavy.

Back in the 90s I had a 430 Detroit and a 10 in a T600 with 3.55s. The 425 cats and the 13s and the 444 Cumins were leaving me for dead. Got a W9 that had a 500 Detroit and a super10 with3.55s. IMHO, there's a huge difference between a 500 Detroit and the 430/470 (I never could tell the difference between a 430 and 470...I had both.)

My current truck has the 3.70s in it. When used for what I bought her for, wide and heavy loads, she does well. Empty, not so well. If I was going to stay with general freight, I would want 3.36s or taller for anything engine over 600 HP.

Anyways, if I had your rig, I would leave the rears along and look into bumping the HP up to 500 or better and going with a 13. The 13 allows you less rpm drop when up shifting, and less you have to raise the rpms for downshifting...in essence, more leverage for the motor. The bigger HP motor will pull the bigger loads easier (read more efficiently) than the smaller engines. Pulling 12 wide and 80000GVW, a 500 Detroit will get better fuel economy than a 430. And it's worlds easier to drive.