Hi. I don't know what items you're specifically looking at , but I do know that there are multiple kits out there all of which cost 5-6 thousand dollars. These kits however, only gain you 99-149 HP. Now, if you do an engine swap to an engine out of gt or boss which bolts perfectly up to your current transmission you get 380 rwhp for the gt and 416 rwhp for the boss. Those are more than substantial gains considering the 3.7 rwhp is about 268. And those engines can be purchased at many different places ranging from 5,955 - 7,599.