Does changing out your final drive to 3.9 or 4.0 change your numbers on the dyno or does the power just come on a lot sooner? I would love ot see a dyno sheet before and after to see how it changes the numbers.

 

Altering drivetrain gears will give not add horsepower. Torque and horsepower charts are different for different final drives. And yes several dynos are posted here.

 

you will see a difference in the chart though. typically, a lower gear will give you lower HP ratings and a smoother curve. if you were to, say, dyno in 3rd and then 4th back to back, you would get the same curve shape, but 4th will give you a higher HP number (same with 1-2, 2-3, 4-5 or w/e you want to pick). essentially, the gears are making your drive shorter, so what is now 4th is more like 3.75 (lol) before the gears. you should se a small loss but not much. nothing significant and the shape will be the same. the power doesnt really come on earlier on the dyno either, it just gets there faster. well i guess it does come earlier time-wise, just not RPM-wise