I'm going to be ordering some gears this week to compliment my T56 install. I'm looking for good fuel economy on the highway so I was going to choose gears based on cruise RPM. My tires are 285/50/20, 31.22" tall.

4.56 = 1718 rpm @ 70 mph
4.88 = 1838 rpm @ 70 mph
5.13 = 1933 rpm @ 70 mph

Right now I'm leaning towards 4.88. But would using 4.56 to reduce the engine speed give me a significant improvement in fuel economy? I'm okay with taking a small hit on acceleration if I can gain 1-2 mpg during cruise.

Thanks!

 

For highway, the 4.56s will help mileage for sure.

 

couldnt you just go with the 4.56, and use 5th if you needed a few more rpms at cruise? use 6th when your on a good flat ground?

 

Of course! One downside of smaller gears would be less of a useful first gear though. 4.56's give me 50 mph in 1st gear at 6500 rpm, and 47 mph with 4.88's. I guess that's not much difference. I'll be cruising in 6th way more often than I'll be at redline in 1st

 

the 4.56's would deff get good highway mileage.. if it was mine, i would install the 4.56's and then if you need more rpm while on the highway for towing or whatever the just drop it in 5th.

 

Is there anyway to calculate slight inclines? For instance if you have a slight grade going up one step in the gears you have listed might make it so your engine does not have to work as hard and therefor burning less gas? Or are they close enough that this really doesn't matter?

 

I guess the reason I asked this question is because if I cruise at lower RPM's, the engine will be making less power and I would need more throttle to maintain the same speed. So at what point does trading RPM with throttle yield the lowest fuel flow? I doubt anyone here has experimented with this.

 

Dunno if anyone has done any test or pulled data for that or not but would love to see some more info on it if someone has. I know guys with lifted trucks and much larger tires have played around with this and used higher gears to turn the tires easier to save gas.


I remember my MPG went up after I got a custom tune when I was N/A (if I stayed out of it). I think one of the biggest thing that contributed to that was after the tune the hills it would normally downshift on while using cruise control and doing 65 it no longer had to.

 

i turn 2000rpms at 70 and averaged 24mpg. i wanna try a taller tire to see if it helps, but im not sure its worth it.. it must be in its sweet spot.

 

24 mpg? How the hell do you manage that?