External flappers are available at most boat stores and marinas. They are modestly
priced and a spare set can be easily stowed in the boat.
Internal flappers come in many different styles and are usually only available through
the manufacturer of the exhaust tip.
Exhaust Flappers
Exhaust flappers are an important component in the engine.  
Flappers are required to keep water from entering the exhaust when the boat operator
cuts the power at speed ("following seas").
Flappers are extremely important when the boat is sitting in a slip or beached with the
engine shut-off.  Waves and wakes can fill up an engine very quickly.
The exhaust flappers should be inspected and replaced regularly.  
External flappers can be inspected at a glance and changed with a screwdriver (while
the boat is in the water!).  
Internal flappers can
not be changed so easily! The boat needs to be pulled from the
water
and the exhaust tips need to be removed from the transom!
The mufflers are 10 inches long with 5 inches
inside the flange and 5 inches outside of the
flange.
Exhaust Tip Kit 4" Stainless Steel
two tips with flappers  580-3-101                   $195.95 pair

Muffler Exhaust Tip Kit 4" Stainless Steel
two tips with flappers 595-3-002                    $245.95 pair

Exhaust Tip Flapper 4" external 89250          $16.95 each

Block-Off Plate for "Y" pipe 560-3-001           $29.95 each
The inlet to the muffler is tapered to funnel the exhaust gases into the muffler from the
4 inch rubber exhaust hose.
The muffler has a 4 inch outside diameter with a 2-1/2 inch inside diameter.
The muffler core is perforated and packed with stainless steel and silences without
restricting exhaust flow.  
The tapered outlet reduces the "rushing air noise" as the fast moving exhaust gases
exit the muffler.
Exhaust Tips
When installing thru-the-transom exhaust the "Y" pipe
should be removed and the hole in the transom assembly
covered with a block-off plate.
"Y" Pipe Block-Off Plate
Exhaust Tips with Mufflers
Questions?  Call Dennis Moore @ 626 357 3573