I'm swapping out my 2.73 rear end for a 4th gen 10 bolt with 3.42's. My car has a 700R4. I don't do too much highway driving, mostly stoplight driving to and from work/school/girlfriends house.

Mainly what I'm concerned about however, is the RPM's I'm going to be running on the highway. Do you guys have any idea what it might run at say, 60mph?

I'd like to get a T56 in the future, but I know it won't happen until probably next year. I'm getting the rear in like a week though.

 

I doubt you'll really see any difference in gas mileage, maybe in the 70+ MPH area...

These equations will do the RPM etc. for you:
https://www.thirdgen.org/calculations

But the answer to your question is:

Assuming 26" tires and a .7 final ratio on the 700R4...

2.73's @ 60 = 1481 RPM
3.42's @ 60 = 1856 RPM

 

Cool. That's not bad at all. I was afraid I was gonna be looking at 3,000rpm's on the way to work...which would not be fun.

 

Yeah, I was gunna say right around 2k. I ran at or just under that with my 3.42's.

 

Yeah, 3.42's are just about perfect with our trannies I'd say.

 

like said above (and the calculations proove it) you wont have any problem at all with mileage.

That is unless, you like to do 90mph on the way to work