There is no such thing as too much horsepower - or is there? The current 2008 model BMW Z4 M makes a total of 330-hp. The recently unveiled 2009 BMW Z4 sDrive35i makes a total of 306-hp and while BMW has yet to reveal details on the 2009 BMW Z4 M we expect it to be quite a bit more powerful than the current 330-hp version or the new 2009 Z4 sDrive35i.
However if you're one of those that may not be content even if BMW ends up dropping 400 horses in the 2009 BMW Z4 M, there is something very unique waiting for you if you're willing to spend 97,900 Euros ($138,727 USD).
A use Hartge tuned BMW Z4 M that is powered by the M5 and M6's 5.0L V10 engine is on sale at mobile.de. But this V10 doesn't make just 507-hp - Hartge has tuned the engine further to extract a total of 551-hp.
You can check out the listing at mobile.de.
Hartge BMW Z4 551-hp 5.0L V10: