I don't want to hijack this thread.
I put a set of JCW turnouts on my bike and immediately noticed that I lost mid and low range power as well as a lot of popping on decel. The bike also got really poor mileage after trying several alternate maps.
I did my research and made the baffles I described above.
I then had the bike on a dyno so that the baffles (which ARE restrictive) could be tailored to suit the bike. I have a friend who has a Dyno and I could spend all the time I wanted using it.
After a lot of playing around I got the baffles to where I am getting the best low and midrange power that I can. It is about 30% quieter although I don't really have any actual DB numbers to base that on.
I know it worked very well for me and was just offering a suggestion.
At first the baffles were too restrictive so I ended up drilling more holes in them to open them up some.
Also you mentioned that the gas would be forced back into the perforations which is not the case on my bike. The gas enters the pipe and exits through the perfs (holes) and then enters another chamber, through more perfs and out the pipe.
The described baffle certainly changed the exhaust note from a very blatty sound to a much smoother note while keeping a very nice low bassy (not much other way to dexribe it) tone.
All the popping is gone and MPG is back up. Kinda sounds like a well tuned muscle car with sidepipes now.
