Ok this spring i plan on re-doing the rearend. I plan on going with a 31 spline trac-loc or eaton (undecided), hardened axles, Alum d/s. The question is 3.55 or 3.73's? I still drive the car alot but is there that much advantage w/ 3.73's vs. fuel mileage?
Also I have 17 inch rims with 235/40/17 front and will have 255/40/17 in the rear. I plan on running slicks at the track (26.5x8.5 probably) on my old ten holes
For sure get the 3.73s. Street or strip. I have them now. I did have 3.55s before. I noticed no difference in gas mileage. Plus if you are going to run the slicks the 3.73s would get you out of the hole better.
I still get 25 mpg on the highway if I PLAY NICE at 70-75. In the city i get 15 or so. You should really get the 3.73s. They are good gear for your mods. The gas mileage will still be good.
Oh man you are going to really love it. I went from 2.73s to 3.55 and that was awsome. But 2.73-3.73 is the good stuff. 3.90s are a good gear also. But 3.73s are a well rounded gear.
Carney - if your car is a 5 speed, you can get a good idea of what the change from 2.73's to 3.73's is gonna be like on the Interstate. Simply downshift from 5th to 4th. The ratio change between 5th and 4th is almost identical to the ratio change between 2.73's and 3.73's. That'll show you how much your revs will change; you can even run some highway fuel mileage runs by not shifting out of 4th.
3:55 TO 3:73 on the highway is about 200 - 300 rpm at 70mph. I have 3:55's and traction is a problem now on the street, but if you plan to drag it then 3:73 and slicks. Good luck. By the way, you will not regret it, you will feel as if your car just gained 100hp.
88Stang - the difference between 3.55's and 3.73's isn't even that many rpm at highway speeds. 3.73/3.55=1.05 -- it's a 5% difference in engine speeds, and at 70, which will be around 2000-2500 rpm, 5% is only 100-125 rpm difference. In my opinion, if you're gonna change the gear and you're trying to decide between 3.55's and 3.73's, I wouldn't let rpm drive the decision. I'd let price, quality, availability drive the decision. There's simply not enough difference between the two to matter much - flip a coin. Especially if you're changing from 2.73's. If you're changing from 3.08's or 3.27's - then the 3.73 makes more sense.
Don't forget to correct your speedo. Here's a link with some info about that.
I have 3.55's--most of my cars have always had 3.73's. I think the 3.55 are good but the 3.73's are a better all around gear. The difference in crusing is minimal but the 73's give you better acceleration.