Run the boat in the water with and without the arrestor. Lig the runs on the Holley. Did it make more boost without the arrestor? Did the computer add more fuel? That will tell you which way is making more power.

BoatNT,

I can tell you the FA was, in fact, collecting belt dust, as I had to clean it off every year. Part of that was how the engine was initially set up when we bought the boat, with the crankcase vent hose just kinda dangling in front of it, so I'm sure a lot of that was a combination of belt dust and oil vapor. I made an adapter that goes between the ProCharger and the FA where I connect that crank vent that, at least, keeps the oil vapor off the breather. I also now have a catch can that that vent hose goes through, so there should be little to no oil vapor getting to the intake tract; the crankcase vent hose simply acts as a vacuum source now.

I certainly get the insurance thing, and the safety thing, in general. But the reality is the intake tract is dry to the valve runner, is about four feet long, and a flame front would have to make it through the intercooler and the ProCharger to get to the FA. Add to that the fact that I've literally never had a backfire.

There very well may be little to no effect from a FA in an NA scenario, but I have to think there would be in a boost application. Anything that reduces restriction is going to increase flow. Physics. Will it make a difference in my application, given the stock heads and exhaust? Maybe, maybe not. Gonna see.

As for Merc and their pursuit of HP.... I've given up on that mindset. They could have easily gotten 500+HP out of the 496, with nothing more than slightly heavier valve springs, a better cam and a proper tune. All they'd have had to do was sell what GM was selling as the HP3. But they didn't. They went after GM legally for it instead. These engines are so incredibly neutered for the sake of longevity and reliability (I get it) it's not funny. In the case of the FA, they simply complied with USCG requirements and went with it. There was probably literally zero lab time involved.

At the end of the day, I can buy a good used OEM FA on eBay for $100, or maybe your K&N for $65. Time will tell.

Thanks. Brad.

UnderPSI,

I would have to build a bellmouth, or this test would be an exercise in failure. In our model boating world, there were a couple guys that did exhaustive testing of carb intake opening shape, and found that a straight tube, with no funneling geometry at all, was the absolute worst-case scenario, short of an inverted funnel. What I would likely do, if I were interested (I am curious), now that I've gutted mine, is to get a non-molested FA and try them back-to-back. But we know a bellmouth is beneficial, because we see the drag guys use them almost exclusively. It is interesting to note that the OEM 496 FA does, in fact, have a bellmouth feature, even if minimal, behind all that restriction.

As it is, we have no way of knowing if this modification actually has any effect, as we've changed several things over the winter that can't not have an effect of its own; smaller ProCharger wheel (from Ø4.25" to Ø4") and a significantly larger cam). We were seeing ~4lbs of boost at WOT (5K RPM) last year, and we expect to see 6 or so in our current configuration. I've made a spanner wrench and added holes in the blower wheel hub so that, in the event MAT is too high, I can go back to the Ø4.25" wheel on the water.

Thanks. Brad.

This thread and post reminded me of when I bought this jet boat with a 468 years back. When I brought it home I noticed it had a PAPER air filter/cleaner on it! Could there BE a worse option to put on a boat?!
Backfire: blow up boat
Splash air filter: blow up motor

Dave,

Ah, yes. The old garden hose. I remember dad blowing these off the water in our blower motor V-drive without even getting into the secondaries. Good times.

Thanks. Brad.

Oh absolutely! There is very little chance but still, anything is possible! Just not a place I would gamble

I was having an engine dyno'ed and for fun decided to remove the arrestor, no difference in numbers on the screen, it was actually 2hp lower but chalked that to variance. Point being there wasnt any reason not to run one in my case

I'll have to swap mine out with some kindling, let's see how she breathes after that

CheckmateScarab,

If you just pulled the FA off, leaving the TB neck bare, THAT was your loss of HP. Had you put a bellmouth on it, you'd have seen a significant increase.

Thanks. Brad.

$478, what are they made of... gold?

Padraig

Padraig,

Totally agree. It's a performance part. Wadaya 'spect?

That was just the first link I came across.

Thanks. Brad.