Originally Posted by
jchamp429
the 13 mpg I get from my 390 could theoretically be doubled if I could build a multi port system that only sprays gas on the combustion stroke.
Not true, I think you are getting your cycles confused. A 4 cycle engine never draws fuel that is not combusted in a "purge" stroke.
Regardless, a well tuned carburetor actually does almost as well as fuel injection. You may gain as little as 1-2 mpg or as much as 3-5 mpg over your carb, depending on how well you have it set up now (but the 13 mpg you are getting now is quite good). The biggest benefits are adaptability and tuneability, and low maintenance.
Good luck with your build, glad I could help.