I've about quit responding to BHAF threads, don't wanna appear biased, but it seems to me that the Napa 2790 I'm running is quiter without the silencer ring than the stock setup without the ring.
I know when I pulled the ring with the stock filter and housing, I put it back in after a long trip. With the BHAF and no ring, all I hear from the drivers seat is very muted turbo noise when making boost. Not at all objectionable. And I've got a 4. 5" open hole in the cowling duct.
RJR
Added in edit; Bill, just reread both your post, if your friend has a properly maintained K&N, that's doing a good job on sealing and filtering, I doubt he'll get much EGT help with any of the BHAF's. Although it doesn't cost much to find out.
Sounds like it's time for a turbo housing change. My 16cm2 worked fine for me till I changed to the #5 plate, now I need a little more help. I've come up with some stainless steel cans originaly used on underground phone line repeaters that may work as BHAF filter housings, there're about 12"x15" and may allow the long sought after (by me at least) dual air inlet BHAF setup.
We'll see.