I have a Bursch muffler on my '74 2.7 too, and I LOVE it !!! The paint have not flaked off, and it took 30 minutes to install the muffler. So I'm pretty happy. Deep mellow sound in idle, and gets really aggressive when it hits 3000 rpms
I have no trouble driving it at highwayspeed. I can still hear my girlfriend, so in fact I wish it was LOUDER !!
I have a terrible clip recorded on a windy day on my cellphone here:
YouTube - 1974 Porsche 911
A better clip will be posted soon................