beefcake

deciding which gear i want to go with

i suppose i'll run a 17" drag radial at the track once i get a stall and converter,

seems like the 3600 stall is the way to go, but wondering which gear would be best as well

3.42, 3.73, or 3.90

if i'm going to stay at the power level i'm at now, i hit 120.46 in the heat with stock gears, whats going to put me going through the traps at the top of 4th, still in 3rd with the 2.56's with a little left

glass slipper

You'll need to know the diameter of the tire to perform the calculation. You can always do a search for online MPH/RPM calculators.

Edit: Here's one for you. http://www.tciauto.com/Products/Tech...alculators.asp

Joe_G

This one's my favorite. Pan down and select your car and trans type. Then you can change tire size or gear ratio or redline and see where you are at.

http://www.xse.com/leres/ss/calculator.html

beefcake

i wish the a6 had the .50 o/d as well

glennhl

The A6 is a different animal. It has very short gears across the board. The A4 has a 1.0 third gear, the A6 has a 1.53 third. Also, it doesn't need the .5 od because it has a 2.56 final drive. Multiply the gear ratio in each gear by the final gear ratio to look at the whole picture.

beefcake

yes, but when you go to a 3.42, 3.73 or better, then that takes the gearset out of the equation

glennhl

If you run a 3.73 or better with the A6, then 1st gear will be useless and all you will do is turn your 6 speed into a 5 speed. Plus, when is the gearset ever out of the equation?

glass slipper

The last time I looked, the equation was (engine torque X transmission gear ratio X rear end ratio) - drivetrain losses = wheel torque. I just assumed he was trying to make some other point and didn't state it very well. Who knows...

Joe_G

Here's an interesting comparison...2 cars VERY similar mods except I've got 3.90 gears and he's got 3.42's. I've got .5 more compression but he's got a FAST.

Here's our dyno sheets overlaid based on RPM on the X-axis. Looks like the same car huh!




But look here - I changed it to MPH on the X-axis, you can see the effect of gears. I have 24 more RWHP at 55 mph up to 47 more at 90 mph! That's why gears make the car feel so peppy.

glass slipper

But at 140 MPH, the 3.42 car has ~430 HP more than you.

carlrx7

if you can hit 140 in the 1/4 then your pulling 9's!!