A couple of quick things...
First off, I have the Staintune collector "box" and I have not noticed any "tinny" sound to it, even when I used it with the stock muffler... Now I run a Neptune muffler, and I still notice no "tinny" sound...
Might just be my hearing, though...
The thickness of the "housing" of the stock catalytic converter is there for two reasons.... Yes, to retain as much heat as possible - 1.) to try and get the cat up to temp as quickly as possible, as cats need to reach a high temp to operate 2.) To try and "trap" the heat as much as possible inside the cat so it doesn't heat the outside air as much as it could, an "insulator, if you will.
Of course, this makes it heavy as all get out.
On DJ's questions about the scavenging, etc. of exhausts... All exhaust systems have "ranges" where they work most efficiently, and by definition, hence also have "ranges" where they work very inefficiently... Such is the nature of a pressure wave and resonant device. At certain RPM's and exhaust pressures the pipes work well to keep any exhaust gas from being drawn back into the combustion chamber, but at other rev ranges they do not do a good job of this and some exhaust gas is reintroduced to the head... This doesn't matter if it is the stock exhaust or a modified exhaust. Further, DJ, even with the cat in place, there is always some exhaust gas upstream of the cat, and so in certain rev ranges it will be drawn back into the combustion chamber. It's pure physics, and is irrefutable. I imagine BMW "tunes" the stock pipe to operate best in the 3,000 to 4,000 RPM band, as that is where the bike will spend most of its life. At lower RPM there is most likely a lot of exhaust and fresh charge mixing in the combustion chamber... And at higher RPM there is little, but the exhaust system "chokes" the breathing a bit.
Actually, any pops and backfires anyone experiences is *NOT* exhaust gas getting back into the combustion chamber... Quite the opposite. Those events are always the result of some *UNBURNED* fuel-air mix getting into the exhaust pipe... And then igniting there. This usually happens when an exhaust system is *overscavenging* - i.e. producing such a strong negative pressure wave in the pipe that some of the incoming fuel-air mix coming into the combustion chamber on valve overlap is drawn into the exhaust system. This is very common on "over-run", when decelerating, as road speed holds RPM high relative to throttle opening (i.e. you have closed the throttle to slow down, but the bike is still rolling along). Due to intake ram and exhaust negative pressure wave effects a relatively high concentration of unburned fuel-air mix is drawn into the pipe, where due to heat and expansion, it spontaneously ignites, causing your pops and backfires...
As for sealing... As of yet I have not found it necessary to use any sealants running my stock R-1150-R head pipes, Staintune collector "box" and either the stock muffler or Neptune. Personally, I abhor exhaust sealant compounds, as in my experience they often cause more problems than they solve. I simply make sure all the junctions are clean and *ROUND* (very important...), and that the clamps I use have good, clean threads and are operating as they should. I use a *VERY* tiny bit of high-temp grease, wiped on *VERY* lighly with a fingertip on all the joints so they can slide together to the proper depth, assemble the exhaust slowly and carefully - with all the junctions loosened aft of the head-to-head-pipe connection (which should be tightened first, if it was ever loosened) until everything is fitted in place... Then I start tightening the most upstream clamps first, keeping everything aligned and in place, and finishing with the aft-most clamps last... Tightening up the muffler hanger bolt after everything else.
So far I have as yet to encounter any sort of exhaust leak or weepage.
Hopefully this answers a few questions...
Oh, and dilligaf... You don't have to worry, or be jealous, either...
Cheers!
Dallara
