# Rear End Ratio change question....



## FlyingDutchMan (Jul 18, 2003)

There has to be another way to get the 3.91 ratio in the rear end of the E46 M3. $2400 is way too much for a ring and pinion. Anyone know the part number or what car the 3.91 gear set comes out of? If so I'd like to find a shop to install it in my car. I'll have the dealer pull the rear center section and then the rear end shop can set the new gears in. 

Anyone attempted this or have any input. It shouldn't cost more than $1000.


---FDM


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## Pinecone (Apr 3, 2002)

FlyingDutchMan said:


> There has to be another way to get the 3.91 ratio in the rear end of the E46 M3. $2400 is way too much for a ring and pinion. Anyone know the part number or what car the 3.91 gear set comes out of? If so I'd like to find a shop to install it in my car. I'll have the dealer pull the rear center section and then the rear end shop can set the new gears in.
> 
> Anyone attempted this or have any input. It shouldn't cost more than $1000.
> 
> ---FDM


1) BMW doesn't sell ring and pinion sets any longer. Only complete pumpkins. And when they did, the r&p set was over a grand.

2) The setup is not as easy as one US diffs, as I understand. So the swap cost is much higher to find someone who can do it right. Also most times, since you have it apart, they rebuilt the LSD, and for non-E46 M3 diffs, they normally adjust the LSD ratio.

3) Not all BMW ring and pinion sets are completely interchangeable without some other parts or work.


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## FlyingDutchMan (Jul 18, 2003)

Pinecone said:


> 1) BMW doesn't sell ring and pinion sets any longer. Only complete pumpkins. And when they did, the r&p set was over a grand.
> 
> 2) The setup is not as easy as one US diffs, as I understand. So the swap cost is much higher to find someone who can do it right. Also most times, since you have it apart, they rebuilt the LSD, and for non-E46 M3 diffs, they normally adjust the LSD ratio.
> 
> 3) Not all BMW ring and pinion sets are completely interchangeable without some other parts or work.


Ah ha....Thanks for the info, is the 3.91 as a complete unit available from the BMW dealer as well? Or only Dinan and Turners?


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## HUMMM 3 (May 10, 2003)

FlyingDutchMan said:


> Ah ha....Thanks for the info, is the 3.91 as a complete unit available from the BMW dealer as well? Or only Dinan and Turners?


Check out the latest issue of Bimmer. There is an article on the Dinan S2 M3. It sheds some light on why the gears cost so much. Economies of scale are really stretched here. You'd run into similar problems if you were to have a gear shop make a small run of parts for just a few customers.


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## SteveMedina (Apr 4, 2003)

we've looked at the 3.91 gear change....and the tracks we run on, it would leave us with a few inbetweens.....

take a look at where ya run....paying special mind to rpms...and see if its worth your while...

a 3.91 where we run, will not take a second away...but that's here....take a look at your fave track, and see if it will help or hurt....


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## HUMMM 3 (May 10, 2003)

I don't track my car, but for someone who does it only makes sense to do the calculations that you apparently did. The downside for me would be range with spirited driving out in the boondocks. In the city it would enable me to keep up with the nitrous rice rockets in the stoplight gran prix. Maybe what we need is a Halibrand quick change rear end.... are they still around?


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## Irrenarzt (May 22, 2003)

3.91 R&P's can be had for 700 shipped from Rogue Engineering. Supply is very limited...


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## Irrenarzt (May 22, 2003)

Sorry that is 700 plus shipping...


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## HUMMM 3 (May 10, 2003)

Thats good info, but I'll stick with the Dinan R&P set. I'm not that handy with tools, in fact I don't have the tools for that kind of work. When the Dinan gear set is installed by the dealer the new car warranty remains in efffect. As Pinecone pointed out this mod should not be attempted by klutzes like myself.


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## Irrenarzt (May 22, 2003)

I have the OEM 3.91 going in soon. I'll post my impressions when I get it all together...


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## Riceeater (Aug 26, 2003)

*try Scott Galaba*

I know he was selling a his spare 3.91 gear set on Roadfly a few weeks ago for like $1K. I bought his suspension and I was considering the gears. From the way he explained it, I got the feeling you need access to a pretty good shop because there is some trail and error involved to get the swap done the right way. you might do a search on Roadfly and see if he still has the gears.


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