I or someone else may have mentioned this in the early days of this thread but I'd like to put a plug in for the GM 3000 industrial engine. It's HP spec is pretty low because its only rated at 3000 rpm but it'll rev quite a bit more than that. The real advantage is that it's a torque monster--well over 160 lb/ft--and the curve is pancake flat. It's huge for a 4, 181cu.in., and it seems more useful in automotive terms than the relatively peaky and much more expensive marine versions. Chevy bellhousings will bolt right up so sticking a T5 or Tremec behind it would be easy. It's not a flyweight but it's over 200 lbs lighter than an SBC so in a light car it should really scoot and likely get 30 plus mpg. The icing on the cake is that with minimal muffling it would sound much more hot roddy than any of the much smaller import bangers. After all it's basically half of a 350 Chevy. It should last forever to boot and although it's a bit pricey at 18-1900 bucks new it might be a bargain compared to chasing all the parts needed to adapt many of the more exotic engines touted in this thread. It's the grunt hog of 4 bangers and as my tag says--torque is king.