I love my RFL. Its very loud. I only ran 4psi at first, initial installation without a boost controller. It would whistle at low rpms (2psi or so), and at full boost of 4psi it sounds exactly like a loud whip. Whaapshhhhhhht. Then at my current 7psi it screams, sounds like a whip, and sorta whistles at the end...hehe. Depends if you keep flooring it or just let off at the end of that gear so it can do its full sequence of noises. Turns heads all the time, seriously literally scares some people.. I remember I startled a pedestrian one time...I floored it and shifted right next to him..he literally ducked and covered his head...I burst out laughing, LOL. Its great.