you are probably looking at around 2 hp peak numbers with the efi on a slip-on. The pipe itself adds about 2-3 hp so around a 5 hp total, the full pipe/efi combo adds a bunch more. The overall ride will be a lot better with the efi combined to slip on only but you will not pick up a lot of peak # or huge gains in the curve. it is a noticable difference when riding it though. The big gains come with the full pipe on this bike