I swear no more muffler questions, but...
 

If I modify my existing dual in/single out Bursch to a dual-out (additional pipe coming out of the right side), can I expect a power increase?

I've seen quotes of an additional 10-13 HP with an OEM sport muffler. Is that in addition to the increase hp with pre-75 HEs, or is that the increase for both?

Would the OEM sport muffler have a higher hp increase than the modified Bursch described above?

Would the increase in hp for a Dansk dual-in/dual-out be the same as that of an OEM sport muffler?

I apologize for the length of these questions, but any help you can give will be greatly appreciated.

Others may disagree but
 

my understanding is that the muffler itself does little to increase HP. This is contrary to some of the ads I see. Maybe if a muffler has a tortuous path, you would see some improvement, but I don't think the OEM muffler suffered from that problem in the extreme. I understand that the combination of SSIs and a free flowing exhaust does give HP increases.

This makes sense in that the largest restriction in air flow out would be the cat converter. The SSIs contribute to HP increase by reducing backpressure and providing a balanced path on both sides. I think the muffler design has more to do with sound than increased HP.

I added SSI's to my 79 and when I talked with the supplier, his opinion was that I would see the same HP increase whether I went with SSIs with dual out or SSIs with single out. I went with the dual out (3") on my car purely for sound and I preferred the dual out look.

Yes autobonrun...
 

I've heard the same - the muffler is for sound more than performance, and that the tuning happens from the SSIs and/or HEs.

So, aside from sound and astethics, is it safe to assume there is no performance difference between the dual-in/dual-out and dual-in/single-out muffler, including that supposed 10-20 hp increase with the OEM sport muffler? (funny, everyplace I look, it seems like the OEM sport muffler gains horsepower - at least in the ad copy)

Thanks.