Howdy - could anybody out there give me a quick estimate of what kind of mileage difference I might see moving from a 2.73 gear (10-bolt) to a 3.27 (9-bolt)?

The car is an '89 IROC 305 TPI with 700R4 tranny. I currently cruise about 74mph @ 2000rpm and average about 24-25mpg.

I have to replace the rear end (tweaked in a wreck), and I've got a line on a good deal for a 3.27 9-bolt (good rear discs, etc). I'm just a little concerned how much mileage I'll lose, as this car is normally my highway car.

Any info appreciated - thanks!

 

On average you'll probably give up a couple mpg. Only you can determine the exact number with your driving style and the condition / combination of the mechanical components of your car. Either way, you'll turn higher rpm's and that will use more fuel. Simple as that.

BTW, is the current rear end a drum braked rear?

Good luck

 

It's a drum rear currently. The replacement I 'm looking at comes with everything for the swap - proportioning valve, e-brake cables, etc...

I realize driving style/conditions/etc factor into the results - I'm just looking for ballpark experiences/observations. I'm willing to give up 1-2mpg, but if it is going to turn out to be 4-5, I need to keep looking for a rear with gearing closer to what I have now.

 

Sounds like you're prepared!

 

I don't know about "prepared" - but I'm definitely ready to get the car back on the road full-time. I took a hit about 14 months ago, and the body shop sat on the car for just over a year (sucks, but I had to save up money for mechanical repairs anyway).

I've been browsing the boards here trying to get all the pieces sorted out, and I think I'm ready to dive in, I just don't wanna give up a lot of mileage. That's been the "sensible" reason for fixing this thing after the wreck - it gets at least 5mpg better than my other ride (a 4cyl Toyota pickup). Granted, "sensible" is a distant second on the list of reasons to keep/fix the car - well behind the fact that it's just fun to drive. :-D

Thanks for the input...