Swap 5spd manual for 6 spd manual

I have a 98 2.8L Z3. I am considering swapping out the 5 spd for a 6 spd. Can this be done; how easily; how much?

I am guessing that the 6th gear would lower hwy RPM which would result in better gas mileage. I spend 80% of my time on the hwy and drive about 80 mi/day.

How is my thinking flawed?

Can be done. Requires the e46m3 6 speed, a shortened drive shaft, and probably a few other odds and ends, but a lot of m coupe guys have done it. I haven't gotten there yet. Most go with more aggressive gearing in the rear at the same time...like a 3.46 or 3.73.

If you get the Evo 6 speed then all you need is the cross member, a rogueengineering.com 6 speed shift kit, and a shortened drive shaft.

The crossmembers are different too? I figured they were the same, but moved towards the rear, using the other set of threaded holes.

Originally Posted by Vinci

The crossmembers are different too?

Yep.

Yeah, different cross members because the tunnel is a bit wider 6 inches farther back I guess.