to bad mercs do not have the right chassis setup for tracks with those wonderful engines... (note: CLK63 black edition - finial gear ep13-1
http://www.finalgear.com/shows/fifthgear/13/1/)
bmw on the other hand has l8ly developed both fantastic engines and chassis that suit them. Shoot, BMW won best engine of the year for 2008 (note M5&M6 -
http://www.businessweek.com/autos/content/may2007/bw20070510_425978.htm)
on the big block street, when you get turbos involved you get "000" followed by any number easily!!! sadly, the cars that use them daily are not daily-able... wheres the a/c bud... (YouTube video-gN6E-_0wXos- 4Sale fastest street car ?? 2000 hp 1963 Pontiac LeMans)
on the tuner scene, rotaries are great where weight per hp is concerned, this of course when reliability is thrown out the widow. from my studies, when tunning engine you can choose from safe, fast, and cheap... but you can only choose 2... pick wisely!! Most of the top engines found on the scene are their because of popularity and accessibility (ie, like the iphone, it might not be the absolute best phone on the market but with its high fan base their are many things available for it)...
but to sum it all down, id like to say my top 5
1- Bugatti Veyron Hermes (1001hp, A/C, radio, etc, ...need i say more)
2- Koenigsegg CCR (and they have a hybrid version, say waaa)
3- Pagani Zonda F (pure sex? dam skippy)
4- Lamborghini LP640 (yes, now KKK turbos... get the picture)
5- Scoot RX7 (although not the fastest, but overall, its nicely put together, and we are all puttin our roots in their.. so, eh..)