I keep looking at Flame arrestors from AZ speed, and some others, but they just look like a K&N filter element. WHat makes them Flame arrestor, or are they just a plain old air cleaner filter element?

I want some Ovals for my 383 HO's I am building, but WOW, 400.00 is a little hard to swallow. Anyone have any suggestions?

Not sure if there is a real difference in the composition of the regular K&N's and the marine ones. The big diff is that one is USCG approved and won't void your insurance with an engine fire.

Yeah, I know that the "Flame Arrestors" are CG approved, I just can't tell the difference, if there is one in the K&N style filters.

K&N makes 2 completely different product lines. The difference between the automotive style "Filters" and the "Marine Flame Arrestors" is their ability to contain sparks or flames in the event of a carburetor backfire.

That ability after testing is why they can display a Coast Guard Approval number which is required on boats with closed engine compartments.

No you cant' tell the difference visually, but their makeup is actually different to achieve the required safety levels.

Flame arresdtor makers are allowed to display an Underwriter's Laboratories number or an SAE number now instead of a USCG number.
SAE J-1928
UL 1111

Actually they're supposed to be stamped to be "legal". The USCG stopped testing products years ago, and all current testing is done by UL or a similar lab.

My (older) K&N flame arrestor had the coast guard number stamped on the cover. When I was selling the boat the appraiser tried telling me that I had an illegal air clean and he was going to report it to the buyer. I pointed to the cover and he shut up. I had the same issue when I was having the boat coast guard inspected. Just remember to clean the filter on a regular basis. My filter had gotten dirty and a healthy back fire caused it to light up. The aircleaner was still smoking heavily when somebody started shouting that I was on fire. At first I dismissed it thinking there was a little fuel burning off but closer inspection revealed the air filter was burning bright red like a cigar butt. I took the air cleaner cover off and threw the filter overboard.

I have Gaffrig flame arrestors with SAE numbers. Whenever my boat gets inspected, whether it's on the lake or sitting at the dock, the flame arrestors are the very first thing they look at. This past summer while we were on Mac Island the boat was inspected by the St. Ignace Coast Guard. They remarked that it was very common to find go-fast boats with "non-certified devices" in place of legal flame arrestors. They completed the inspection, I got the gold copy certifying compliance and everyone was happy.