I had my 3.90 Motive gears installed over the weekend. And anyone that is on the fence about 3.73's or 3.90's, I recommend the 3.90's whether you do lot's of Hwy driving or not. I haven't yet recalibrated my speedo (debating on speedcal or Diablo Predator), but on the highway I keep up with the flow of traffic in the fast lane (70ish mph) and I'm running about 2500 - 2700 rpm in 5th. I haven't yet been able to really lay into it, but it really pulls in 2nd & 3rd with just half throttle. Just my .02.

 

Thanks for the info. Ive been thinking about changing the gears in mine.

 

Still waiting to do mine.
Ill just wait till my SCT Xcal is here.

 

I swapped my 3.90 rear for a stronger complete unit with 31 spline axles and detroit 31 spline locker plus it had 4.10 gears. I can feel the slight difference stepping up to 4.10s. I went with 3.90 after everyone saying go 3.90 with a power adder, when i shouldve went 4.10s all along.

My 97 mustang has a a mechanical to computer speedo. So i still needed a Speed Cal, even thouh i have a SCT 4 position chip. Sucks i had to buy the Speed Cal, I did think the SCT would do it.

The speed cal was easy to hook up it says an hour time, but only took 15 minutes to do. Plus you can go on their site and put in your tire size and Axle ratio, and really fine tune it. Your tire size affects it too. So you cant just set it by changing the dipswitch 3.27 to 4.10s. Nice Feature. It lets you calibrate in increments of .2% steps!!

Get at least 3.90s if you have a Mod motor and get a tune to remove the Rev limitor if you cant go fast enough or worried about running out of steam at the end of the quarter. After going 3.90 to 4.10s, no way id be happy with 3.73, If I had one of the newer mustangs with the .62 Overdrive instead of my .68 id be all over the 4.30s, since my car was mostly built for the track and not commuting.

 

You definitely will not be sorry going with 3.90's. And I'm sure the 4.10's pull much harder. This is a must do upgrade!!!

 

There is little difference between 4.10's and 3.90's. So little, that I oftenr think it just makes more sense to get 4.10's. Either way, you are in good shape.