I'm afraid I'm not going to be much help with this today. Something else I'm working on is taking up my time. I'll look some more and get back to you tomorrow. In the meantime, if it was my car, I really, really like this tip. It's a dual tip and has a resonator. It says sound levels will be determined by the size of the piping, etc.:bow:
If you went this route with 3" straight pipe from the resonator on back to this tip, I bet it would be real close to what you want! Besides, it's looks like a BMW tip!! The link to this hot tip is below, with another page to check out the links on. I'm actually in the midst of doing my exhaust on my 540I. I think I'm actually going to get this tip!!
Even with a V8, I'm going with a single, large (3" dia.), pipe from the resonator on back to the tip. It's basically a single from the factory anyway. You won't get much gains from just an exhaust system. You'll get more with a quality set of headers and good exhaust, like I linked to you earlier. Then add a good tune, which is a must with headers. With headers and a good tune, you may see 25-35 HP. That's about the best bang for your buck, without opening up the engine, going with a supercharger, or adding a small nitrous kit, which is on my list.
GREAT looking tip!!
More to peruse...