Ok, "nothing" is exaggerated. But, with no power adder it is going to be minimal. So why spend money on a minimal difference.
Drop in gas mileage...are you kidding me. 5th gear is now useable, you can drive around in a higher gear than before. My gas mileage stayed the same and I was beating on it more it seemed....and that was with 4.10's. After 3 months the 4.10's seemed like the gear the car should have came with and I was wanting a bigger gear. This is all while I was still n/a.
SicStang....you say you purchased 3.73's....but haven't installed them and you want to say I'm wrong.
I've driven in a Cobra with 3.27, 3.73's, 4.10's and now 4.30 gears....I think I may have a clue here.
Oh, and if this IS a track car...do NOT put 4.10's in your car. You shift right before the traps.....this puts you at the beginning of your power band, not at the end. 4.56 gears are a great drag gear for an n/a car. 4.10's suck.
Put 3.73's in if you want...I'm telling you, unless you drive like an old fart, you will be bored silly in 2 weeks and will kick yourself for spending money on a useless mod. The only time 3.73 gears would be good is if you went with a roots blower and started making crazy torque down low.
Listen to some other people after they start posting....