/6 4bll intake.

I ":super sixed" my 63 wagon and the mileage went up from about 15 ish to almost 20 . It was explaned to me that the 2 barrell atomizes the feul beter than the 1 bbl causing better effeciancy(sp). The 2 1/4 " exhaust had something to do with my great mileage improvment. People have successfully tuned 1 bbls to the 20's though(light early a bodies).