12 Second N/A Slant 6?

I say bump the compression way up, do some head work, and make it run on E-85 then making 260 horsepower is pretty possible. Any more power than that, you will need to do custom pistons, custom rods, and some crank work.

Search google for naturally aspirated slant sixes and I think mopar muscle magazine did a slant six build that made 320 horsepower but they had a lot of work (aka money) into the build.