Longer 6th gear in urS4/S6

[URSIMPO]

Is it possible to make the 6th gear in the 01E gearbox longer? I find that 6th gear gives me 70mph at 3000rpm - the same as a 5th gear on other cars. As I am giving my car alot more horsepwer, I feel that that an extra long 6th gear would give a much higher maximum speed.

[UrS4boy]

Is it possible to make the 6th gear in the 01E gearbox longer? I find that 6th gear gives me 70mph at 3000rpm - the same as a 5th gear on other cars. As I am giving my car alot more horsepwer, I feel that that an extra long 6th gear would give a much higher maximum speed.

Have a look here:

http://www.elektro.com/~audi/01E/

What you likely want is a B5 S4 / C5 A6 2.7tt DSY or EDU 6spd:

3.50 1.89 1.32 1.03 0.81 0.68

Dave F.

[UrS4boy]

.... As I am giving my car alot more horsepwer, I feel that that an extra long 6th gear would give a much higher maximum speed.

On the test tracks and maybe the Autobahn, the C4 UrS4 had a top speed of 150 real mph, limited by the stock horsepower and aerodynamic drag. This occurs well below red line so the transmission gearing really has not much to do with top speed. Since aerodynamic drag goes up with the square of the velocity, the overall power requirements to push the car through the air increase with the cube of the velocity.

True, more hp means more speed (and acceleration getting to that speed) but you need a lot more hp to go just a little bit faster (than 150 mph). The graph in the post below might help you:

http://forums.audiworld.com/s4s6/msgs/170818.phtml

Dave F.

[caterpillar]

change the final ratio too 3,889... in the rear, and find a tranny with 3,889...6tr tranny WITH 3,889 may be the tricky part maybee....

[S2central.net]

To do this from first principles...

Get the rolling radius of wheel. 16" wheel has 8" radius plus whatever nominal height from tyre - which is 55% of 205mm for a 205/55 tyre. Thats a nominal rolling radius of 0.316m (your actual tyres may differ from that slightly of course). Lets call that 'R' here.

Assume an engine speed of 'E' for now in rpm.

For a Gear Ratio 'G' and a Final Drive Ration 'D' we have the formula for speed as follows --->

S = ((E/G)/D) * (2*PI*R) in units of meters per minute

So for these inputs

E = 1000 rpm
G = 0.729 in 6th for a CGR/CRB (well its 27/37 more accurately derived from gear tooth numbers)
D = 4.111 (actually 37/9)
R = 0.316 m

We get 661.724 meters per min => 39.7kph and 24.7 mph.

Therefore a LOWER value of D or G will deliver higher road speed for the same engine speed (assuming you have sufficient power to overcome additional aero and rolling losses).

Alternatively LARGER rolling radius will also increase road speed.

Paul

[Audi_CQ]

Use a 6th gear from a diesel 'box.

[URSIMPO]

I wil start with big wheels then

[newsh]

Yep, by far the easiest way, remember your speedo will be out when overtaking police cars and going past scameras

[URSIMPO]

scameras. ha