I have a 2011 Chevy HD with deletion and a 5" straight pipe exhaust, had a very pathetic roar at 40 mph and again at 70 mph. I recently bought a car', after much research I settled on MBRP. If professionally installed I would say the noise was reduced by 50%, my wife says closer to 70%. But what is the difference , I'm very happy with this product and results, VERY careful it won't do OEM silently if that's your goal keep looking lol.