You can't modify the trans for 6 gears. A 6spd trans from a euro M3 or US E46 330i would probably be easiest but would probably cost around $2000 USD. Is that worth it for a few more mpg?
My ti can get 34-35mpg when I'm driving all hwy with 3.73 gears and keeping it around 70mph. I'd imagine a 3.25 rear end would be a great compromise towards more efficiency without sacrificing too much performance.
Also, ditch the giant heavy wheels. That alone made a HUGE difference for me, 3-4 more mpg, and much better handling, acceleration, and braking. __________________ ~Dave~
98 328ti Morea Grun slicktop
11 128i space gray slicktop
13 JGC WK2 Deep Cherry
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