Question(s) for TheFermanator

[Destroyer]

Ferm, just a quick question, followed by a comment and maybe another question if I can phrase it correctly. A while back, in a different thread, you made the statement that you shouldn't run an engine with the air box off the front. I have no problem accepting the validity of your statement, because you're a hell of a lot smarter than I about such things. But my question is... why? Specifically, what damage will it do to the engine without it.?
Which brings me to my second statement/question. (And again I admit that I'm a dunce about these things, so I figure that asking you is my safest bet on getting the correct answer)
Outboard engines don't have air filters on them, yet they suck in tons of air. Why don't they have some kind of filter? An I/O has a filter on the intake manifold, so why not an outboard?

There's no particular reason for me asking these questions other than I'm curious as to the reasons. It's the engineer in me.. I have to/need to know how thihgs work. Thanks

[THEFERMANATOR]

Outboards run on the water, and you tend to not get alot of dust and debris when out on the water so air filters aren't a big neccesity. As for running without the airbox, the carbs ar jetted for the restriction from the factory. If you add air, you have to jet up about 6 sizes for an OMC to compensate for the airbox removal(but 6 sizes is the MINUMUM and you have to be careful at that to check it). The OEM's use the airbox as a restrictor to help smooth out the mid range transition some and to keep them from leaning out in the mid range. This helps the driveability of the engine, but means you have to jet down some on the top end to keep it at a good fuel air ratio. The old 200XP from 86-87 didn't have a restrictor in the airbox, but they had 74 jets whereas the 225 with the restrictor would have 65's or close to that in them. The 200XP's ran AWESOME on the top end with there MASSIVE carbs and open airbox, but they were known for burning up if ran in the mid range for extended periods and many were converted over under warranty to the 225 set-up due to it.

And I haven't seen many I/O's with air filters on them. ALL of them do have flame arrestors, but this is for USCG requirements. They look like air cleaners, but they flow alot of air and are only there to prevent flames from the intake catchong any vapors on fire in the bilge in case of a back-fire. Some do use a K&N filter for qa spark arrestor, but it is mostly for the USCG regs and not for filtering.

[willy]

I shocked the crap out of myself I actually knew those answers too, must be from all the talking I do with Ferm Skools and Spare on the phone.
Maybe a few years from now I will be able to find my arse in the dark.

[Destroyer]

Originally Posted by THEFERMANATOR

Outboards run on the water, and you tend to not get alot of dust and debris when out on the water so air filters aren't a big neccesity. As for running without the airbox, the carbs ar jetted for the restriction from the factory. If you add air, you have to jet up about 6 sizes for an OMC to compensate for the airbox removal(but 6 sizes is the MINUMUM and you have to be careful at that to check it). The OEM's use the airbox as a restrictor to help smooth out the mid range transition some and to keep them from leaning out in the mid range. This helps the driveability of the engine, but means you have to jet down some on the top end to keep it at a good fuel air ratio. The old 200XP from 86-87 didn't have a restrictor in the airbox, but they had 74 jets whereas the 225 with the restrictor would have 65's or close to that in them. The 200XP's ran AWESOME on the top end with there MASSIVE carbs and open airbox, but they were known for burning up if ran in the mid range for extended periods and many were converted over under warranty to the 225 set-up due to it.

And I haven't seen many I/O's with air filters on them. ALL of them do have flame arrestors, but this is for USCG requirements. They look like air cleaners, but they flow alot of air and are only there to prevent flames from the intake catchong any vapors on fire in the bilge in case of a back-fire. Some do use a K&N filter for qa spark arrestor, but it is mostly for the USCG regs and not for filtering.

Ferm, thank you. That's kinda what I thought on the restrictor side of the answer. Not sure if I agree with the factory(s) on no filters, but that's just the Navy and the engineer sides of me talking... I've been at sea long enough to know that even in the middle of the ocean the dust and especially the salt will dirty up anything left unprotected.

My old V with the I/O setup had a flame arrestor in it, but it had a really thin filter between the inside and the outside metal mesh. Come to think of it, I think it may have been a K&N brand.

In all cases, thanks for the swift and (as usual) informative reply... One more thing to add to the storehouse of knowledge tucked away in my crainum.

And Willy, you live close enough to Forked River.. you arse should glow at night making it easy to find.

[nipper]

The replacement 4.3 litre V6 I put in my 91 V20 cuddy in 2004 (new) just has a flame arrester and no filters, at least not as it came from the factory.

[RidgeRunner]

I thought I knew the answers too. Never played with jet sizes too much. Scared to ruin a motor.