I bought one of those for my mazda about 10 years ago while living in Guam, I noticed no difference. I guess the ultimate test would be to run some 0-60 times,or even better a dyno, but I am still in the "snake oil" camp on this one. If it were that easy to improve performance, I would think auto manufacturers would do it, and big name upgrade companies would market them as well with a Jegs sticker or some equivalent.