I have one of those old style flame arrestors. I had no idea there was a newer version that flowed less.
The k&n from the procharger kit (works on n.a. apps with the tb adapter) is pn re-0920.
Can make a unbelievable difference in intake noise in some cases

When we redid mine a couple months back, we ran the newer stock flame arrestor and then swapped to the K & N style (not the one with alum end plate, it's like the one CP Performance sells) and it was 1 hp difference.

That's on stock 502.

So was your new style flame arrestor the flat one with silver plates in it? I have seen 2 different KN 502 mag air filters, the big square one like posted by bg3 and aone with a necked down adapter, sorta like a procharger inlet adapter with a conical clamp on filter, that one looks restrictive

Smitty - Here are some pics of the style of K & N that I have on my 502.
It is conical in shape and I believe it has more surface area than the Vortech style.

Thats the one I have seen pictures of and consider it as posssibly restrictive. The reason why is my Baja 272's previous engine was a 540 that made 1100 hp blown and a best of 657 NA on the dyno. I had 2 ecu's, one witha NA tune, one with a blower tune and I could swap ecus, pull blower belt off (or in some cases cut what was left of it out of the pulleys), swap props and boat. With the intake manifold and 56mm throttle body im testing on THIS 502 on my old 540 the boat ran a best of 76mph (no blower) and that was with the procharger throttle body adapter off the throttle body, with it on (and its very similar to yours) the boat lost a solid 1-2 mph, even with no element, just the adapter , maybe Ill find one to test locally while Im wrapping this up, Smitty

Did you make any pulls with no flame arrestor at all?

That procharger adapter did look super restrictive . That was one i had left over from a kit.went to a guy putting a mag intake and stand alone in a 454 suburban. Prob wasnt as bad with a blower on the other side of it.
i would be curious how inlet temps at flame arrestor from say 90° to 120° affect hp numbers on that 502
at 76mph i wonder what you would of gained by squaring the transom

I don't think we did. They made 436/438 between the 2 motors at 5000.

was thinking that too, the procharger one was built w expectation that aur would be pushed thru it so its not as radiased as the kn. Back when i tuned my 540 na and ran boat that was a few times i even tried pulling air thru the innercooler w idea maybe cold air would give it more hp but it slowed boat down even further. I also built a really cool bellmouth radiased entry piece for the procharger adapter for running na but it didnt help.

I built this bellmouth on a metal lathe with sandpaper and a tool steel cutter from a 3x4 pvc coupling, really thought it would help air into the procharger adapter running na but it didnt help