FWIW...the Dynomax Super Turbo mufflers sound good, but are VERY restrictive. We've had 3 different pairs of mufflers on my dad's 440-6 road runner. Started off w/ Dynomax UltraFlows...sounded great, but were a lil too loud for him, so I swapped them out for some Super Turbos. He loved the sound, but you could definitely feel the car did not have the power it did before. He eventually got tired of that and I put a pair of Hooker Aerochamber mufflers on it for him. They are the best of both worlds in my opinion. Definitely feels like it got the power back, louder than the Super Turbo mufflers, but not as loud as the UltraFlows. He's happy!