# tail gears and rpm



## nboost (Oct 25, 2010)

I picked up a 06 a4 a couple months ago from a dealer and he said there had been rear end work done to the car but could not prove that to me other than what he was told. On the way to work today, I decided to take it for a little burst on the highway briefly and noticed at 120 mph, i was already at about 5500 rpm. Does this sound right? Seems like lots of members have pretty crazy top speeds where as it seemed like I was going to red line quickly. I don't care to do 150+ down that freeway, just simply want to see if I have what sounds like a lower tail gear.


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## jpalamar (Jul 22, 2008)

What gear where you in at 120MPG and 5500RPM?

If I remember right, your probally at the end of 3rd in the auto?


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## nboost (Oct 25, 2010)

Im almost positive I was in OD already. Im not too sure as to where the autos shift at at WOT. Maybe I ought to give it a go manually shifting through the gears..


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## Poncho Dan (Jun 30, 2009)

Sounds like maybe 3.91's. That'd set you pretty close to those numbers.


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## GTO JUDGE (May 14, 2005)

Jack the rear end up, allow the rear tires to be turned, turn one tire one revolution then count how many times the the drive shaft turns to one complete spin of the tire.

If you turn your rear tire one turn and the drive shaft at the rear diff turns just under 4 times you will be close to the 3.9's. This will give you a good idea the gears you have.


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## RJ_05GTO (Jul 6, 2008)

Poncho Dan said:


> Sounds like maybe 3.91's. That'd set you pretty close to those numbers.


Would 3.91's knock the top speed down that much? With the stock 3.46's the car should top out well over 160mph without the limiter. I guess he could squeeze out another 10 mph or more with 500 or so rpm left. I was thinking about putting 3.91's in my car but I cant find too many people running them with a A4 to get info on how they perform. I might have to go with the 3.73's but i dont know if it will be worth it for the money.


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## RJ_05GTO (Jul 6, 2008)

I checked out a couple of rear end ratio calculators and it does look like it should top out in 3rd gear at a little over 120mph if it does have 3.91's but that is at 6200 rpm. Maybe you let off of it before it went into 4th. It almost sounds like stock gearing if you were at 120mph passing over 5500 rpm in third gear. It shifts into 4th at around 6000 rpm. The way I see it either you have stock gears and didnt shift into 4th before you let off at 120mph or you have really steep gears way steeper than 3.91's if you were topping out in 4th gear at 120ish mph.


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## Poncho Dan (Jun 30, 2009)

I'd actually like a set of 3.73's for my M6... it shouldn't affect mileage too much, but put me in a better RPM range in 6th gear @55, plus give me a mild accelerative boost.


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## 68greengoat (Sep 15, 2005)

Merry Christmas everyone..............:seeya:


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## 87GN06GTO07IRL (Aug 10, 2009)

RJ_05GTO said:


> Would 3.91's knock the top speed down that much?


Your not going to hit redline in 6th with any gear. 3.91's or 4.10's will give the car a tiny bit of pull in 6th. I've never been in a race where i needed 6th, so with that being said a 3.91 will get you to the top of 5th the quickest. 4.10's, even quicker.


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## RJ_05GTO (Jul 6, 2008)

06gtoin216 said:


> Your not going to hit redline in 6th with any gear. 3.91's or 4.10's will give the car a tiny bit of pull in 6th. I've never been in a race where i needed 6th, so with that being said a 3.91 will get you to the top of 5th the quickest. 4.10's, even quicker.


Oh yes I know they would work great with the 6 speed but we are talking about the automatic. After doing a little figuring I think the 3.91's will work fine with the auto. I dont care if I lose a little gas milage and top speed. I have yet to go much over 130mph so it shouldnt matter.


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