That's what it had. So I tested with and without. I was out tuning the boat that day. Carb, timing, props, etc. 2nd to last test was with muffler inserts with and without. Last, was the Arrestor.

Just Looked up my notes and they state: 1.6mph by removing it's K&N #59-3364. 68.1 mph without vs 65.5 with,. Edit: I believe notes where a typo and is supposed to be 66.5 with KN Arrestor.

I am no mathmetician, but I believe that is 2.6MPH

I would like to see some dyno sheets on this 1000hp NA engine with a dominator.

Oh snap. That's my computer notes taken from my written notes. Written notes are long gone of course.

It was a bunch of years (7 or 8?) ago but I would believe the 1.6mph as I remember just under 2mph for the FA and just about +2mph from removing the muffler inserts in the tailpipes. That boat gained good mph that day playing with it. The 68.1mph was correct as I have a pic of the GPS as part of my notes.

I have the k&n on the new 502 and the stock merc on the 454 should I use the stock one on my 502?

Well let me clarify. I doubt in real world conditions you are going to see any speed increases with Merc HP style flame arrestor, vs a Gil vs K&N, ect in a 26' Baja. Yes if you slap on a merc 330 arrestor you are going to choke the engine and lose speed. On the same hand, I kind of doubt if you spent to the money to build a 600 hp engine your going to slap that on your carb. When I was trying to squeeze every last MPH out of my 242 Formula, which had a very well built engine in it, I tried all sorts of arrestors and it didn't make any difference what was on top of the carb, but that is just my experience.

i think the k&n will be fine for stock power.

maybe it had a 400 hp shot of nitrous.

I understand you have scoop but without one for anyone, next time raise your engine hatch some if possible to see if you pick up some rpms & speed. On some boats the air flowing cork in the bottle is the how well the engine compartments are sealed up not allowing enough clean fresh air to enter along with holding heat.

Merc years ago had a SB about checking raised temps in the engine compartment and make sure not to exceed 176 degrees inwhich can promote vapor lock. Also as we all know higher air temps & engine compartment temps you lose hp numbers.. IMO it is better to reduce engine compartment temps and allow fresh air to enter and heated air to escape better, before worrying about which flame arrestor to use..

Me to waiting on a set of heads from CFE about 3 weeks out.