Jason- It depends what you consider smooth is. The last engine you bought from me was a GRP .21 with a non tuned case, GRP .28 crank with the turbo cuts and a GRP .21 onroad piston and sleeve. That thing was fast If you are looking to get another one from me, I would definately go with the P5 with full race port and 9901SS and 41021 header for smoother delivery. If you are looking for a little more low end punch, the 9853SS with the same header is a good choice and if you are looking for all low end and midrange, the 41020 header on either pipe will be way to go.