I am planning on replacing the carburetors on my 7.4 litres with Holleys and also was considering replacing the factory flame arrestors because they seem restrictive. Some friends tell me that all K&N filters & housings are all OK for marine use but I noticed that K&N sells a marine line but they cost 3-4 times as much as their automotive line. Can anybody shed any light on this? Thanks.

Got to say "marine" to be USCG approved. I got my complete filter and SS top and bottom for less than $100 at Summit. Part # KNN-59-3364.

Will they all function effectively as flame arrestors??? Maybe - maybe not: it really doesn't matter from a legal perspective cause if it doesn't have the USCG approval stamp on it then it isn't legal and your insurance will balk if you have a fire issue and they are able to discover the use of non approved parts.

My guess - since K&N fabric elements all contain a wire supporting mesh within the fabric I would expect them to be effective flame arrestors.

I have even heard, though, that USCG approved K&N's will catch fire under the right conditions (be aware, though, that flame arrestors do NOT have to be "unburnable", they just have to be able to stop a flamefront due to backfire).

The K&N marine filter element is exactly the same as the regular elements. You're paying the extra money for a SS enclosure with is stamped with the approval number. And yes, I've actually had one of their elements catch on fire. Apparently fire is not covered under the million mile warantee.

The filter is not exactly the same. I have two and one is marine, one isnt. Both the same size. The marine version has a more heavy duty stainles steel mesh inside the filter than the auto which just has a thin wire mesh. The thing I dont like about the marine is that it is short. I run a K&N stub stack under mine and the top of the stack is just below the lid. Thats why I bought a taller auto one to try. Didnt make a difference anyhow.

I just bought a 5 inch tall K&N marine flame arrester from CP performance. Part number is 59-3370. Total height is 61/4 inch. My stock merc was 2 inches tall and 3 inch total. Also the merc is 8 inch diam. and the K&N is 9 inch. I don't expect any performance gain, but I can use more air to my engine, so I figured it couldn't hurt. Plus it looks real nice

So, let me play a little devil's advocate. With the very little amount of "mileage" that a boat engine actaully sees compared to an auto and the very little amount of "crap" that needs to truly be filtered while on the water, the onlything a K&N may give you is increased flow.

So, why not just use a larger flame arrestor? I made a double height flame arrestor from two Merc stock arrestors and I gotta believe it will outflow any K&N filter.

I just bought one from summit.
59-3364 I think it was $87.95

Thanks for the input from everybody. The local speed shop quoted me $75 for the regular and $290 for the marine version. They looked the same and I wasn't sure. It sounds like there are some better deals on the web.

I bought mine from CP performence. It was 129 bucks. If you have the room go for the 59-3370. Good luck!