I took a look at my diff ratio today while doing my brakes, and found that i have 3.73 gears. Could this be the cause of my poor mileage? id like to get some better top speed and better all round mpg.

Do i go up numerically? or down? is 4.54 better? or worse for fuel economy? what is an all around good ratio? for 90-100km/h highway driving, and 50km/h city driving. mostly city driving.

Mark

 

I'm no mechanic but the way I understand it the higher the gear ratio the more engine revolutions per every drive shaft revolution. So... if you want good mileage you want a low ratio, but that will give you less power. My truck came with 4.11 gears which meant tons of low end torque but crummy highway mileage. I believe 3.7 gears are already a pretty good compromise between mileage and power. If you want better mileage you should go down, not up, but that will cost you low end power.

 

3.73 is a good all around gear.
my truck has 3.42 and its a little of a dog towing.
if you had 4.10 or 4.56 youd get bad mileage, 3.73 shouldnt be all that bad, but wont be the best. if you were to change them, the money it costs would not pay for itself for quite a while i dont think.
a taller gear like my 3.42 is worse in town light to light driving.
with the 30" tires on the highway in overdrive it almost struggles to keep itself rolling at 65mph.
1800 rpm is a good highway cruise RPM for most V8 engines to get decent mileage, depending on the cam thats in it.

 

3.73 is a perfect balance. 3.42 is the lowest I would go if I were you. When I had my dually, it had 4.56 gears and was a hoss off the line but that five speed still couldn't get it over 114 (speeds by radar) but got 8 mpg. When that truck had a four speed transmission it was even worse, topped at 107 and 6 mpg. I know of a guy around town who has a 2.73 in his late 70's camaro. It's a dog off the line but after 120 it keeps pulling (slowly still) so there is a "too much" and a "not enough"

 

1Gary, racerx55, and 98white5.0 are all right, IMO. 373s are a great all-around gear ratio.

In the event you want better mileage, and you can live with giving up low end power, 342s will give you better MPG and much quieter RPMs at highway speeds. If you travel a lot, or drive a lot on the highway, I recommend them wholeheartedly.

That said, a conversion costs about 2,000$ out the door. If I didn't travel so much, I'd have been thrilled to stick with the brawny 410s the truck originally came with.

The later model Silverados have two issues at the time of conversion. You must reprogram your PCM (thru your OBD II plug) or your speedometer will be inaccurate, and your ABS sensor will trip at highway speed. See if you can get the shop where you're having the work done to do this for you.

 

I have 3:73's, a 350, hills, and a heavy foot and I get about 15.5 MPG

 

It all depends on tire size. I have 4:56 but I have 35 inch tires.

 

I would agree with the majority here and stick with the 3.73 unless you have put on taller tires, it's not cheap to do and will take a long time to repay in fuel savings.