L99 A6 - Looking to do a Gear Swap

[DaveRoc27]

L99 A6 - Looking to do a Gear Swap.. What kind of RPM loss can be expected @ 70-75 mph crusing speed? Right now I'm @ 1900-2000 rpm at that speed.. Debating between 4.10 & 3.73..

Thanks, Dave

[GJG]

[Supercharged SS]

Originally Posted by DaveRoc27

L99 A6 - Looking to do a Gear Swap.. What kind of RPM loss can be expected @ 70-75 mph crusing speed? Right now I'm @ 1900-2000 rpm at that speed.. Debating between 4.10 & 3.73..

Thanks, Dave

Dave, you will be gaing RPM with the lower gear, not losing it. I'm about to swap in 4.10's in my A6 this wk. I would GUESS that the new cruise range may be 2-300 higher with the 4.10. Someone that knows for sure will chime in.

[DaveRoc27]

I consider it a loss at cruising speed if it's at higher rpm.. If you have too low of a gear and you are going down the freeway 70mph @ 3000rpm, NO BUENO.. I want lower gears but don't want a drag car.. Still want a road trip worthy ride.. 2-300 rpm with a 4.10 sounds perfect.. But I need actual #'s

Originally Posted by Supercharged SS

Dave, you will be gaing RPM with the lower gear, not losing it. I'm about to swap in 4.10's in my A6 this wk. I would GUESS that the new cruise range may be 2-300 higher with the 4.10. Someone that knows for sure will chime in.

[Supercharged SS]

Originally Posted by DaveRoc27

I consider it a loss at cruising speed if it's at higher rpm.. If you have too low of a gear and you are going down the freeway 70mph @ 3000rpm, NO BUENO.. I want lower gears but don't want a drag car.. Still want a road trip worthy ride.. 2-300 rpm with a 4.10 sounds perfect.. But I need actual #'s

I got you. We just word it differently. I know for a fact that the info youre looking for is on this site. I just don't know where. Like all the haters will tell you......SEARCH. If I come across it I will get it to you. Actually, conatct wacker. I'm pretty sure he's and A6 and did the 4.10 swap plus he's a tuner and logs his info. We were talking about similar stuff with the gears a few days ago but not about h-way speeds but I bet he has the answers. Gd luck.

[GJG]

Rear End Gears 101

[GQ4Life]

http://vexer.com/automotive-tools/speed-rpm-calculator
handy tool.
Remember numbers on top are correct, guage for visual
remember to change tires size along with all the gears.

Camaro5wiki for gear ratios
http://www.camaro5.com/forums/wiki.p...tions+%28SS%29

[Apex Motorsports]

Originally Posted by DaveRoc27

L99 A6 - Looking to do a Gear Swap.. What kind of RPM loss can be expected @ 70-75 mph crusing speed? Right now I'm @ 1900-2000 rpm at that speed.. Debating between 4.10 & 3.73..

Thanks, Dave

Dave,

With 3.73s you will be turning 2050 RPM at 70 MPH and with 4.10s you would be turning 2250 RPM. 4.10 is extremely aggressive on the low end in the A6 because the transmission is geared more aggressively than the M6. I generally recommend the 3.73s for street A6 applications. If you have any questions feel free to hit me up.

Chase

[GQ4Life]

I agree with Apex Chase
4.10s very aggressive on A6 especially if you are running a lot more then factory HP you will spin a lot without some good slicks.

[DaveRoc27]

Thanks Guys. Chase, those were the exact #'s I was lookin for. I plan to do a supercharger in the future, so it sounds like I may want a 3.73 to have a good all around gear, although the 4.10 sounds damn tempting..

Here is what I dug up from the links above:


The formula used for determining RPM given MPH, axle gear ratio, transmission gear ratio, and tire size is the following:

mph X 336.1524 X final drive ratio X transmission gear ratio ÷ tire diameter (inches)

Or, the un-simplified long version:

mph X 12 (inches per foot) X 5280 (feet per mile) X axle gear ratio X transmission gear ratio
pi (3.14159265) X tire diameter X 60 (minutes per hour)

Hydra-Matic 6l80 six-speed automatic (A6 SS) w/ TAPshift
Gear ratios (:1):
First: 4.03
Second: 2.36
Third: 1.53
Fourth: 1.15
Fifth: 0.85
Sixth: 0.67
Reverse: 3.06
Final drive ratio: 3.27

TR6060 six-speed manual (M6 SS)
Gear ratios (:1):
First: 3.01
Second: 2.07
Third: 1.43
Fourth: 1.00
Fifth: 0.84
Sixth: 0.57
Reverse: 3.28
Final drive ratio: 3.45



So, for me this equation with stock tires @ 28.7" tall and 6th gear trans ratio of .67

@ 70mph w/ 4.10 = 2252rpm

@ 75mph w/ 4.10 = 2414rpm

@ 70mph w/ 3.73 = 2048rpm

@ 75mph w/ 3.73 = 2195rpm

@ 80mph w/ 3.37 = 2341rpm

[danhr]

for an A6, if you have to ask, go with the 3.73's.

You have no idea what you are in for with the 4.10's....

[Apex Motorsports]

Originally Posted by DaveRoc27

Thanks Guys. Chase, those were the exact #'s I was lookin for. I plan to do a supercharger in the future, so it sounds like I may want a 3.73 to have a good all around gear, although the 4.10 sounds damn tempting..

If forced induction is in the cards just forget the 4.10s.

[Supercharged SS]

Originally Posted by danhr

for an A6, if you have to ask, go with the 3.73's.

You have no idea what you are in for with the 4.10's....

I have no idea but we are doing mine next week, 4.10s that is. Should make for an interesting launch! Yee Haw!

[danhr]

Originally Posted by Supercharged SS

I have no idea but we are doing mine next week, 4.10s that is. Should make for an interesting launch! Yee Haw!

well you're special.

I am curious to see if those 28x10x17's hold......

and what you are going to 60' now.... that's gonna be a hellacious 1st gear, if they hook.