Dave is on target. I have used them all. SU's, 4bbl and 2bbl. All have there unique qualities. But you just can't use POS carbs and expect them to perform. Start out with fresh parts and you will get good results. I love my downdraft setups. I have a JDM downdraft manifold for a factory 2bbl,also a clifford research and Arizona Z brand manifolds. In the past Chevy and Ford and Chryler has used a 1 bbl downdraft carb in the past with good results on their straight six engines. A good seal and a low CFM carb is the ticket be it a side draft or down draft setup. Too much CFM for a 2400cc to 2800cc will actually lower horsepower according to bench dyno's.