It's not about HP. It's about throttle response.
I was pleasantly surprised by how easy it was to install. It does whistle when you step on the throttle but I do feel more response when I hit the gas. To me it kinda sounds a bit like a turbo. Overall, I think it's worth the money. Keep in mind I also have the AFE cold air intake to go with it. I haven't seen a difference in the MPG's but it's only been on my truck for about a week.