I was on the fence with this purchase, but decided to go for it so I would have it in case I went somewhere with noise regs. In short, I could definitely tell the difference on my 660 Raptor. W/O the quiet core, the Raptor took off like a rocket. With the quiet core, it's still better than stock, but much more sedated. The product is very well made and installs in about 5 minutes. I'd give it more stars if it didn't suck as much power away. Good value for the money.