Have any of you noticed a change in max rpms by changing to an aftermarket flame arrestor?

No, Unless you have a very little or very dirty one.

Same results for me. No change in performance but looks better.

There is a pretty interesting artical in one of the latest issues of one of the performance boat magazines concerning flame arrestors. They dyno tested an engine with about 5-6 different aftermarket flame arrestors against the stock Merc flame arrestor. They even tried some of the real expensive, oval shaped, billet machined aftermarket flame arrestors-------well, they turned out to be VERY disappointing! They were very restrictive (some more than others) and thus killed HP. The Merc actually gave the best horsepower results and let the engine breath the way it should.

If I remember correctly, they made mention that while doing this they did not make any jet changes in the carb and it showed to have caused lean conditions within the engine being dyno tested. Therefore, I think the author of the artical cautioned about going out and buying an aftermarket flame arrestor, and just bolting it on your engine(s).

The only disappointing thing about the artical (I felt) was that they did not try any of the K&N air filters. I personally have the Coast Gaurd approved K&N's that comes with a mini velocity stack. And while dyno testing my engines with an "open" carb a couple of years ago, I found that once we bolted the K&N air filter/spark arrestor on the engine, made a pull on the dyno and it actually picked up 3hp without any warning signs that we could see.

Better than a sharp stick in the eye!

Tried a k&n on a 502 magnum, 75.5mph before vs 75.5mph after, multiple runs on GPS before & after..........Nothing..............

You guys must be doing something wrong. I bolted one of them thar breathers on mine and picked up 10mph.

Hey, it's not written in stone gang. I don't believe speed was the point I was really trying to make. Whether a boat will increase speed or not, I was actually suprised that by bolting an air filter/flame arrestor (whether it was a K&N or any other) on an otherwise "open" carb----that it actually gained HP vs a loss in power----hence a better breathing flame arrestor whether it was 3hp or 30hp.

I think the more important point about the article they were trying to stress (if I recall) was not to just go out and buy a flame arrestor and bolt it on an engine for fear of a possible lean condition/higher EGT's without doing some plug checks.

I just thought it was some interesting info to pass along.

KAAMA makes a good point. I do get a kick out of the ads I see though about bolting on 15-25 hps with a flame arrestor.

mine is very little and very dirty... but how did you know?