I hope in the 5 months since you asked this question you realized that changing your gears in NO WAY affects your HP rating. They will give you a mechanical advantage over other cars and make you faster, but your HP rating should stay the same. (BTW I'm not trying to sound dickish, so sorry if it seems that way)

 

.5 sec? jeez i thought that .2 at the most will be good ... or who is wrong here?

 

Gears may nottechnically add HP, but your butt dyno will beg to differ. Gears make the motor come alive. What it does is make your motor wind up quicker. You'll have to shift much sooner with 3.73s
than with the stock 3.31s.

 

Gears have nothing to do with HP, they just make your car accelerate faster or slower. For example a stock GT makes 300hp at the Flywheel, if you cruise at 20 mph you'll accelerate much faster if you are in 1st than if you are in 2nd. and the power is the same, all you did was change the transmission ratio (gear). In the same fashion if you change the diff gear you'll accelerate faster if you have 4.10 than if you have 3.30, the power remains the same.