I tried one on my Dyno, gained 0.5hp after 6000rpm. The main reason to use one is the extra rev so if you don't need that you should save your money.
And some people have had starting problems with them, others say they work fine. I don't know since I only tried it a few runs on the dyno
And some people have had starting problems with them, others say they work fine. I don't know since I only tried it a few runs on the dyno