flame arrestor - increasing height

Have any of you guys adding something under the flame arrestor to raise the height?

I've seen a couple of posts and one guy at my marina mentioned it. He said it really made a difference. I'm not "what' was used though.

Do they sell something specific or is it just a matter of making something?

I can probably go another 2-3". Mark, I thought you posted sometime back "not use the gasket under the arrestor". Did I get that right? My boat didn't have any but not a big surprise after twenty years. The kits that Cliff sells does come with them.


Bob

Bob,

I know costs can be a factor but those K&N marine filters are replacements for your flame arrestors. You can get them in sizes much taller than my actually fit but with careful clearance measurements, might you not be better off with greater intake volume potential. I looked into them but I can barely gain 1/2 " with confidence so given the cost, I kept what I have but would have liked to get larger ones.

Good Memory! A gasket under the flame arrestor provides an exit path for gasoline in an extreme flooding scenario.

Did your marina buddy quantify the 'difference' made?

What i'm getting at is the improvement you are seeking. My guess is you won't see any noticeable difference anywhere in the operating band unless you have a 'thin' flame arrestor. Going to a 'thick' arrestor will help the upper rpm band due to less pressure drop (more area). They also provide a 'straightening' effect for the air entering the carb.

When we had the thick arrestor installed, the throttle response was improved but not nearly as much as when the exhaust system was opened up. Sadly, we didn't have the clearance to make it a permanent feature (and still don't).

Mark,

The guy who did it thought he felt a little better response after making the change. He's a mechanic by trade and was surprised by the results so I tend to believe him.

I have about 4" to play with so every little bit might help. How thick is the "thick" arrestor? I'm might already have that installed from Crusader already.

The other guy who did this also removed the diverter from the exhaust "Y" and I was planning on doing this as well.

Is that what you are referring to?

Bob

Bob:

My stock thin ones are about an inch tall, for the inlet portion of the arrestor. The thick one I got was close to 2.5" along the same spot. It's in the basement so, if you are interested, I can measure later.

On the exhaust, we went from 3" at the elbows to 4" out of the Y, into the muffler and 4" out the transom. When done, 4" elbows to the Y pipe, 5" out of Y pipe, thru the mufflers and 5" out the transom.

If the existing pressure drop is tolerable, you can get the straightening effect by inserting a staight piece of pipe between the air horn flange and the arrestor base. also need a longer stud to keep it all together. 2" should be enogh to get the desired effect.

Mark,

I'll be going to the boat later today and will check it out. Just to clarify, the "inlet" is what makes contacts with the carb correct? (i.e., where the paper gasket installs).

I wasn't sure if the filtering part of the arrestor got thicker also.

I was using "inlet" to refer to the air intake on the arrestor. Some have the close spaced 'fins' and others have a screen. If you look up 'flame arrestor' in the parts section of this site, you can see several and get the gist of what was referenced.

I have doubts about the size of the flame arrestor making any significant difference. They aren't that restrictive. What may help is a spacer between the carb and the intake manifold. This increases the effective runner length of the ports, isolates the carb from engine heat and improves emulsification of the air/gas mixture. These are available from Jegs, Summit, Napa etc. Again, not gonna feel it in the "seat of your pants" but maybe over a years' worth of time it'll save a few bucks in gas money.

I have a another question that's similar - would any improvement be noted if fresh and "cooler" air was ducted to carbs from outside engine compartment?

Cooler air is more dense and therefore would improve efficiency of an internal combustion engine.

Are you likely to notice the difference- probably not.