lanesteven4570.

My truck has the e40d trans. With push button over drive

lanesteven4570.

E4od with push button over drive

Brandon587

Ok so you have a .71 over drive ratio. I would play with online calculators like I said to find what ratio you would be ok with rpm wise. Most online calculators do it as a 1.00 trans ratio, or a direct drive through the trans, which for the e4od and most four speed autos is third. So just take that answer and multiply it by .71 and that's your rpm in forth gear.

PerryB

Brandon, are you still lovin' the Truetrac? Mine's in right now getting 4.56's and I'm thinking about dumping the TracLok and going with the Truetrac. Actually would like to put them in both ends (thats the beauty of the Truetrac) but I just can't bring myself to spend that kind of money.

PerryB

I ran the numbers on your tire diameter, factoring for 3.73 gears. These numbers are in 4th gear (.71)

60 mph = 1785 rpm
70 mph = 2082 rpm
80 mph = 2380 rpm

Those are very comfortable numbers.
I based my calc's on an actual tire diam. of 30".

lanesteven4570.

What kind of fuel Mileage would you expect out of my truck with that gear combination PeryB

Brandon587

That would actually work pretty well being that at 70 you would be running peak torque. And as long as you don't like traveling much faster for long periods of time. I personally don't know about mpg. If you live in a hilly area and the truck has to downshift a lot to go up hills, then it may help or at least balance out. If your completely flat it may get a little worse in the interstate but not tank. What do you get now?

Brandon587

I still feel 3.55 would work better for better mph and all around performance. Not that 3.73 is too much, but it's more of an all out pulling ratio for the 300 if your going on the interstate in my opinion.

lanesteven4570.

The areas around me are somewhat flat but we do have some hills. They are long and tall. I'm using going up and down 4 to 5 hills a day on my commute back and forth to school.

Do you think mpg would be better or worse on interstate with 3.55 or 3.73. After may I'll be doing 90% driving on interstate

Brandon587

Well knowing that I would for sure look more into 3.55s. Look around on Google for people who have geared there's and see what they say. I just feel that with your circumstances 3.55s are best. Unless you plan on running a bigger tire in future.