Manhart Racing is offering V8 & V10 upgrades to BMW Z4's, ranges run from 400 to 755HP. No word on prices but rumor on the German forums puts the packages at Euro 30K to 50K. Required also are mods to the suspension and brakes, some conversions require the 7speed SMG tranny. Check it out at
http://www.manhart-racing.de/DE/cont...orumbauten.htm
Might be a cheaper way to get a Z4 GT3 equivalent for a lot less money