Open Exhaust

[Checkmate21]

I'm looking for info on how to open up my exhaust. I have a Merc 220 EFI. I've seen this done in a magazine a couple of years ago. They had fitted two flapps that opened up above the water line to releive the exhaust before exitting the prop. Is this safe for the engine? If there are kit's out there, who sell's them?
Any response would be appreciated.

[exciter]

LAND AND SEA,OR BOB'S SELL KITS.OR YOU COULD DRILL 1/2" HOLES IN EXHAUST ABOVE CAV. PLATE.THEN IF YOU WANT TO CLOSE THEM USE 1/4-20 BOLTS WITH A PIECE OF HOSE A WASHER AND NUT(LIKE A DRAINPLUG).
YOU NEED TO FATTEN UP THE HI SPEED JETS.OTHER THAT NOISE IT'S NOT REALLY FASTER

[snappertapper]

i ahve also heard you need to pull the powerhead and take out the exhaust liner then if you want to be fancy you can put a tuner in there

[HavasuDreamin']

snappertapper:
i ahve also heard you need to pull the powerhead and take out the exhaust liner then if you want to be fancy you can put a tuner in thereCorrect, and the whole schbang should net you about 20 - 25 hp.