Brewster

Use my mustang mostly as a commuter on interstate. V6, 5 speed manual, pony package. No mods yet. Any mods I make will hopefully help mileage as well as acceleration. I can keep my foot out of it most of the time, I am old.

On way home tonite I got to watching DICcalculate mileageand at times at around 70, it almost seemed to do better in 4th rather than 5th gear. This is at around 5200 feet altitude and some gentle hills on I-25 between Denver and Fort Collins. So, I got to thinking that even on interstate commuting the 3.73s might be as good or better than stock for gas mileage at this altitude and rollingterrain.

What are your experiences concerning gas mileage and switch to 3.73s ??? How much of an RPM difference do the gears make ?

I notice about 2100 in 4th at 70 and 2800 in 5th. This is with stock gears, pony package tires and wheels. Anybody know the calculation to figure RPMs with gear change ?

Also how are other mods work at altitude. Do these cars run richer at high altitude, or does the stock computer tune as well as aftermarket tunes compensate ???

Steven6095

I got a nice milage increase with my 3.73s and my Bamachips tune. No long have numbers, but it was very nice.
Mainly city driving and car was in power range quicker, etc.

wolfey2k

Hi, don't you mean the other way around regarding RPM @ x speed?
I thinkyou meant 2800 in 4thand 2100 in 5th gear right?
I am going to be installing an x pipe true dual 'cat back' system and a posi-traction differential in a couple weeks.
I was considering going up to 3.73 gears myself while I have the rear end torn down.
It has 3.31 stock in it right now and it's a 5 speed automatic.
Only has 3200 miles on it so far.
I'd like to know how others are doing with 3.73's too.
We all know we'll get more power to the wheels but I am not too sure about gas mileage and I don't want to have to tear the rear end apart again if I am not happy with MPG after the changup.
One other thing though. Since I have an automatic, I have overdrive. Sticks don't but I'm not sure if 5th gear in a manual tranny is equivelant ratio wise to an automatic in overdrive.
Oh and I don't live that far above sea level. I think it's less than 100 feet above on average here.

mustangman02232

you will loose 1mpg if that with 3.73s and another 1 on top of that for 4.10s (total of 2)

mpsautosalvage.com has used 3.73s for $50, there is absolutely nothing wrong with used gears

you need a tuner to correct the speedo, talk to justin at vmptuning.com, he is flat out the best tuner out there

and you also need a bering kit from americanmuscle.com the discount code is mustangboards

while you are in there, it is not needed but you should get a ford trash-lok or detroit true trac LSD

Brewster

Absolutely, I meant2800 in 4thand 2100 in 5th gear right?