The Borla mufflers were born out of sound restriction necessity, they are good for about a 6-7 db reduction in noise level and are said to not "rob" any HP, on the race boat "Rockdodger" we ran Shotguns and they were only good for a 2-4 db reduction in noise and cost a bunch of dough (ours cost $600).

The reason was that the river marathon races instituted noise level restrictions and those that did not comply got 1 minute added to each leg of the race they did not comply, harsh, very harsh.  These guys were completing a 38 mile leg in just over 20 min., the new number to beat is 18:22, thats minutes

These mufflers sound extremely cool attached to crossover headers (AKA 180* headers.)

There's a large contingent of folks running Borlas up here due to the noise issues. Most are blower boats.  I've yet to hear them run but will have lots of opportunity this coming weekend and will post up my thoughts.

For what it's worth, my Bassetts with the baffles are terribly loud.  I too am looking for a solution to the noise.

I think Rods are copies, says they're loud as fuc. Said people hear him above all other boats, can hear him comming WAY down the river.

Here's some to wet your appetite. I thought I had some better shots but I guess not. Regardless, I should have ample opportunity this weekend.

PO PO fucn w/ me about mine now

Seems to be a reoccuring trend everywhere.

Well, I got to hear a number of these things this last weekend.  At idle they are very quiet with a nice rumble. Don't know if they'd still pass the sound check but they are much more pleasing to the ear.
Once you stand on it they bark like a monster!  Very loud and cool sounding but certainly not any quieter than a set of Bassetts with Baffles run dry and way louder than a set of Bassetts, Baffles and water.

I'm going to guess they are for pressure gauges, I saw one a jet like that before.  But I could be wrong as I am illiterate when it come to the pump.