how about something completely different?
7.0L duramax diesel? cappable of ~700fwhp with stock air and fuel system, and more than double that with aftermark fuel/air systems.. ~5500rpm redline. and 35+mpg
weighs little more than a iron head BBC.. though they have an aluminum block coming out $$$$$$
http://www.socaldiesel.com/SoCal%20D...oker%20Kit.htm
the audi R18diesel as won the 24 lemans last 12? times?