I have new 540's in my Formula 272 SR1. Finally had a chance to uncork it and found it didn't have what HP500s have in 35 foot boats
Beat my head against the wall along with my engine builder. 3/4 throttle would get me 75/76 mph (GPS). WOT not much more . On the dyno they did 625hp and 702 ft lb tq
After the third time out and I was scrubbing the black soot off the back of the boat it hit me . Reread the boxes my nice K&N filters came in where it shows it flowing 887cfm. Read the real fine print and found that was for a 3 1/2" X 12" filter...not the 2 3/4" X 9" filter found in their 59-0284 "MARINE" filter for a Dominator. So I call them up and start to explain. There answer "Oh yeah , we know thats to small" WTF Why you selling it then? Got some B. S. answer. They said I could PURCHASE a 59-1197 filter assembly but couldn't just purchase the filter. Finally they agreed to exchange filters for the $ difference but I have to send them my existing filters and being on opposite sides of the country , unless I "red label" them. I'm looking at 2 weeks.
Any suggestions for other good flame arrestors??

The K&N's are restrictive even if you have the right one ....
Alot of people say they gained lots of speed and power on the dyno by just using the large wire mesh type flame aresters ,and not an actual paper filter . "Excavator" on the board , said he saw drastic difference on the dyno ! You know ,you don't realy see much "dust" out on the water ! Just my .02 JOE

Boot,
Notice I said Flame arrestors not filters , I know what you mean about dust on the water

Did you try running them with the arrestors off just to see if they were making a negative impact? Another thought that comes to mind is engine room ventilation. Try running with the engine hatch off?

After that, all the normal things come to mind like total advance, jetting etc. What are you running for props and WOT rpm?

Be patient, optimizing takes time and usually some setbacks. My engines will probably be wore out by the time I get done optimizing

BT

OK , feel free to jump in here
Come on Bobby Daniels...No words of wisdom

When I had my 540's on the dyno, we picked up 3hp going from an "open" carb to the K&N air filter with the reddish paper element in it. Can't remember the part number on my K&N filters, but they are about 8-9 inches tall.

So you guys are saying NOT to use the K&N paper element filter---and that I would get better results without them? Thanks

Ah ha, maybe thats where the power went on one of my engines with the KN on it. Ill have to take it off and see what happens.

Kaama,
K&N sells a #59-0284 for a dominator carb that has a 2 3/4" X 9" filter for a Dominator. That doesn't flow enough for a 540. Worst part is they know it and even admitted that to me. That only flows about 568 cfm , you 8 or 9 incher should flow 3X that. That's fine but I'll bet it doesn't have a USCG number on the filter element itself. According to K&N they only sell a 2 3/4 " and a 5" high marine filter
A 540 @ 5000 rpm requires about 780 cfm and about 830 @ 5500rpm. Depending on compression , cam size and volumetric efficiency perhaps a little more. You should be fine with yours
I don't have 8 or 9 inches , if you know what I mean.

OOOOOOOOOOOOOOOkay ,
Got some big azz arrestors from Eddie Marine. Sez I can suck the engine hatch through them....well . You get the point

5" X 10"