the jp3 and 4 are 3 chamber pipes and lack top end they are also fuel hogs,the jammin 2 is my choice pipe if i wanted to stay with jammin.
the ofna 086 w/round header(or dynamite 86)is amazing with the force .28 and i trust you wont use anything else once you try it.
i have tried all these pipes on my nephews lx buggy with the force .28 so i speak from experience.