I changed my Mercruiser air filter with a K & N on my 496 HO in a 28 Heat. The results are that I lost rpms and top speed. I drove the boat for about 3 hrs thinking maybe a break in period but no improvement.

My experience is that the K & N air filter was a waste of money and I put the Mercrusier air filter back on.

I've heard that experience from others as well. What kind of speed are you seeing your Heat?

Total waste....you don't really need an air filter in a boat. The flame arrestor is just that, nothing more. You can't get any less restrictive than the screen for the 496. If you have any doubts, take it off and run it, there is no difference. I would think that the K&N just makes it harder to breathe.

I have read that the stock flame arestor has better airflow than the K&Ns on the 496.