Streetable 12 second 20+ mpg slant six?

Yeah it's all based on what the OPs final goals are. The one thing that makes up for the /6 power vs the V8 is the equalizer of the turbo. I be willing to say that a stock 6 could make similar hp before 3000 rpm compared to a big cammed 318. After that, it's on boost. Plus the 6 is built stronger than a 318 so it's turbo-ready, and equipped with super low compression pistons. V8s make power no matter what with a lot of cheap, proven combos from mild to extreme. It's all about what ya want.