and a bare 353 deck in the background.

That may be my new Sport

Wouldn't it be legal in all states if the thru hull was muffled too?

only legal if it meets DB requirements.

Exhaust 101-B.The Porters do not like loud boats and will not build one that will not meet requirements in all states,hence the Corsa mufflers. They work well with a a nice legal rumble sound.Captn's Call has never been an issue in states that outlaw "exhaust cutout devices" because the boats meet DB requirements in all cases,open or closed.

The y-pipe with or without the switchable option is a definite plus if done properly to avoid reversion jissues (reversion is less of an issue on newer efi/IAC engines, still highly dependent on the cam). It reduces backpressure and db level over the same muffler system without the extra path. It allows more overall flow area than just a transom mounted muffler and more internal volume to buffer exhaust pulses (lower db level and peak pressure). I have seen the difference on a boat that had older Gil clamp on mufflers with silent choice. The silent choice was removed and there was a definite speed loss. Put the silent choice back in, speed came back. Keep in mind that the silent choice valve, open or closed, allows exhaust to go out through the drive as an extra way for backpressure to bleed off. The biggest problem on performance engines and exhaust is that it usually requires the water dump earlier in the tailpipe, therefore it's easier for reversion to be an issue.

I just received this info from Formula.All 06 Fastechs have as std equipment Corsa Quick and Quite systems. This is thru hull tips with mufflers plus the Y-pipe. It is NOT switchable,that is an option,as always. I'm not sure of all the reasons behind it but I don't see any negatives here. One positive I can see, if someone buys a standard 06 and wants to add Captn's Call later,it will be much easier and cheaper to do.

what are those motors ?

Those are MX 6.2 MPI's, optional engines for the 292 Fastech. GM small blocks. 6.2 liter / 377 cubic inch (4.00" bore X 3.75" stroke) and rated at 320 hp at the prop. Click on the link for more info.

http://www.mercurymarine.com/mx_6.2_mpi_sd_-_320_hp

My 353 does not have the box, only the corsa mufflers but unfortunately it still vibrates my swim ladder at idle. Kind of annoying