Aluminum Slant 6 engine

The aluminum Slant-6 is nifty and cool (in that "I have something not many other people have" kind of way), but it's not a hot ticket to awesome MPGs. You save 80 pounds, that's it.

If you're trying to build a max-mileage maker, it'll be much more cost-effective to build a top-notch 170 engine and save the aluminum-block money for an EFI setup instead.