I started off with my 01' running about 151hp with stock everything. Went with 2 Brothers oval cans and a BMC airfilter, which was about 160hp. Start with a little bit if you are not real inteested in just Hp (like sound looks etc.). Slip- ons are not cheap but I ran mine for about 4 months, and then sold them when I went to a full system. Part of the fun for me was doing a little bit at a time. I just finished doing some healthy Mods this weekend which takes me up 187hp (waiting for good weather). Just do what your comfy. with. Slip ons have a great deep sound if that is what you are interested in, and will get you maybe 1 1/2- 2 1/2 add'l hp.