I did some reading on guys who have compared the 6.1 and 6.4 intake and the 6.4 made more HP than a stock 6.1 pretty much all the time and was real close to a ported 6.1, everyone was belly aching they couldn't port the 6.4 because its plastic. I would bet that with compression maximized for the plastic ones superior heat insulating properties the 6.4 would make more HP than even a ported 6.1 but if compression is not optimized and just straight up swap the ported 6.1 still wins. It also seems the 5.7 eagle truck intake was righ there in the mix and maybe even a hair better than the 6.4 but because of the hood clearance issue was not practical for a lot of cars. There is a lot of info on the internet machine if you can wade through the guys thinking a hellcat hood turns their R/T into a hellcat.