e85 3.0i 5-speed auto to 3.0si 6-speed auto conversion

[MadsLarsen]

Hello everybody
I have been doing a lot of driving on the highway,in my z4, in the past year. But i have gotten pretty tired of not having a 6th gear. So i was wondering if anyone had any tips or warnings about swapping from an e85 3.0i 5-speed auto to a 3.0si 6-speed auto?

thanks in advance
-Mads

 

[deltasierra]

I found that out a few days after I bought the 5 speed, so swapped the car for 2.5si with 6 speed auto, almost as much power (218hp) as the 3.0i. A low milage 3.0si Auto is going to be expensive, the 2.5si is much less, I added Cruise and Electric Seats its really great and comfortable cruiser. You also have a sport button if you want to be a hooligan it changes the car completely

 

[Zedebee]

To clarify, are you asking about changing the car or changing the gearbox?

Personally I find the grunty nature of the 3.0i M54 suits the 5 speed auto quite well, although
if I ever get back in a coupe (3.0Si N52), I will look for an auto too.

 

[Rockhopper]

If you want to replicate the Si then you’ll need to change the differential as well as the final drive ratios are different.
Also do your sums - it’s way beyond my mathematical abilities but it’s possible that the 6th gear is exactly the same as 5th in the five speed box and you just have closer spaced gears in between to allow you to keep the engine closer to its optimum rev range.

 

[Zedebee]

Indeed. isn’t the simple solution just to change the final drive ratio?

 

[deltasierra]

Useful charts but they are all for manual cars, autos are sure to be different, changing the diff ration would be a far simpler solution, finding one that fits your car might not be so easy.
For touring it’s not about the ultimate performance, it’s about driving on an Autoroute at 130kph (85mph) at sensible RPM

 

[Rockhopper]

Well spotted! What i said is still true though (the ratios will be different) plus the gear box ECU will be programmed to change gears to suit the torque characteristics of the different engine. So I'd guess you also need someone who is capable of re-mapping the gearbox or it might end up changing gears at the wrong time.