[PremiumPony]

What's the O/D For in my 2007 mustang ?? Over/Drive whats that for ?

[05horse]

od is your final drive gear.
lowers your rpms
saves gas

once you get up to speed turn it on ur rpms go down

4th gear is 1:1 for every 1 rpm in to the tranny, 1 rpm comes out.

5th gear is 1:X (X= 5th gear) witch means for every 1 rpm put in its miltiplied and output by the final gear.

lets say first gear in 2000 RPM out 1000
second in 2000 out 1300
third in 2000 out 1600
fourth in 2000 out 2000
fifth in 2000 out 2300

as you can see since more is comeing out than comeing in your makeing positive power to gas ratios

more rpms mean higher speed, but with less gas

[PremiumPony]

when i press the O/D button,it displays on my board as O/D OFF,that's good for when im gonna race someone ?

[05horse]

well when ur gonna race i doubt ull hit 5th gear, but yes, leave it off to race, and usually in the city.
like tight city. if your gonna hit 40-45 mph id go ahead and leave it on.

never hurts