With the twins there's alot more piping, resulting in alot less space and things having to be moved around/rerouted. which can be a pain in the ass.......twins will be a bit shorter spool time and can make more power. Example: hellions single 76 is maxed out at around 850hp, My Twin 57 THP kit will make somewhere between 900-1000hp. However if I did it all over again I would have went with the hellion single, 900-1000 on the street is going to be a waste, i'm sure 800-850 would have been fine. So with that being said its all about lag time and HP levels you looking for.