The experience that I've had with Splitfires is that they don't work. In addition, I've also seen where they actually deteriorate very quickly. The commercials say you'll see gains, but remember, when you change to Splitfires, it's usually because you're old plugs are worn out, therefore any plugs will help you out. I would go with NGK or something similar to that. There's a reason that some plug companies have been around for years. As for the K&N, I've noticed a difference with it on my Harley, but the thing to remember with that is if you get more air, you're going to need to get more fuel. If the K&N or similar filter is put in without rejetting, it could actually hurt performance. If I'm completely of my rocker here fellas, pipe in.