I just added magnaflow 4" mufflers as resonators on my 70 Charger. I just got back from the test drive and it's a sucess. No more drone at 40 & 60 MPH. It still has a very deep sounding idle, a little deeper than I'd like but not bad. Driving is great. Sounds nice but you can listen to the radio with the windows up at 60 MPH. The only bad thing is I now hear a lot more noises that were covered up by the exhaust.