Outboard motors adjustable for altitude

[Fishman38]

This may not be the most appropriate place  for this topic but being impressed with the knowledge base I find here, thought I'd give it a go.  The 1983 70 hp Johnson on my old johnboat is a very good machine............at or near sea level.  However the only way to adjust for altitude is basically by trial and error changing high and low speed jets, a total of six of them since its 3 cyl with a carb for each, as well as prop size and/or pitch.  Not very convenient if you want to fish occasionally at sea level as well as in the mountains!  There's probably nothing to be done about the prop issue, which is no big deal anyway, but can anyone tell me whether any of the later model outboard motors are equipped with electronic controlled fuel injection systems that may solve the fuel mixture problem and/or possibly equipped with a turbocharger?  Or even with manual hi and lo speed manual mixture controls as we (at least used to) find on the small single carb motors. 

[Fishman38]

I found an article online that answers the first two questions and they are "yes" and "yes".  The article didn't address the third question but the answer to it is probably "no" since the answers to the first two are "yes".   BTW this article talked about two stroke engines only.

 

The article also didn't address how these new technologies handle performances at different altitudes so if anyone out there has experience with that issue I'd love to hear from you.  Seems to me that these motors would handle altitude changes as well as modern cars do.   

[PAR]

I don't know of any outboards equipped with a turbo, nor why you'd want one, though an intercooler would be an interesting set of engineering problems, not to mention keeping the powerhead cover from melting, if so equipped.

 

The bigger 4 strokes can adjust to altitude changes if a real EFI setup with a MAF. Only the newest and bigger engines are setup like this, as the smaller (portable) engines fall under a different set of EPA and DOT guidelines. If you are looking at a new 70 HP, then the Honda seems the best choice, in this regard, though maintenance and consumable replacement, is much more costly than carb equipped engines.

[Fishman38]

Thanks for the input PAR.  The only reason I might want a turbocharged boat engine would be to compensate for the power loss due to lower air density at higher altitude and I assume they'd have to be designed to adjust fuel to air ratio as well.  I don't remember the exact rate of power loss with increasing altitude but I once calculated that my 70 hp sea level rated Johnson would rate about 45 or 50 hp at 9000 feet where I often fish.  I think it's 3% for every 1000 feet.  And that's only if the fuel mixture is correct.  BTW I read that one company is marketing or about to market a turbocharged outboard but only in the 300 hp range. 

 

But no, at some point I'll be looking for a larger motor probably 90 to 115 hp, for the Ocracoke 20 I'm building and hoping to find one that can handle the high altitude better than the '83 Johnson 70 I have as well as near sea level occasionally.   Also a new boat warrants at least a newer motor  .  I'm just trying to learn more about what's available so I know what to look for when that time comes.

The bigger 4 strokes can adjust to altitude changes if a real EFI setup with a MAF.

 

What does MAF mean?  I've seen lots of motors for sale that claim EFI, some I think in the 90-115 range but don't remember seeing the MAF part.  I guess I more or less assumed that any Electronic Fuel Injection system would adjust for changing atmospheric pressure.  

[hokeyhydro]

MAF = Mass Air Flow Sensor. Fuel injected cars use them along with several other sensors to maximize engine/fuel efficiency and minimize nasty emissions.

[PAR]

The Mass air flow sensor is part of a series of monitoring devices, to optimize the air fuel charge in the cylinders. Technically, the MAF senses volume, not density, but other devices in concert with the MAF can offset altitude changes. The engine still has to work with a decreased air density, but at least it can regulate the air/fuel mixture to compensate as much as practical.

 

A turbo is a fine way to make a little engine produce bigger engine power, but the draw backs can be considerable. For the HP you're looking for, a turbo would be a great way to cook a little motor, that's trying to be bigger than it really is. With the exception of high output engines, where forced induction is desirable for some reason, normally aspirated engines are decidedly the better way to go.

 

If you expect high altitude use frequently, select a bigger engine and learn to throttle back when lower. It's a difficult set of conditions to ask of any engine, so you'll probably need to make a hard choice as to which way you go - convenience adjusting mixture settings or a more high tech approach with it's related costs and temperament. If you go the high tech route, it may be possible to have a button that re-maps the EMC, one setting for altitude, the other for sea level. This will mean some aftermarket devices or possible a swap out for the EMC for each situation. Check with the engine manufacture to see what's available for high altitude operation.

[Fishman38]

PAR, a tip of my hat for a great post sir, exactly the kind of information I was looking for.  And gee, I've always had the impression it was a relatively simple issue in small airplane engines!  Now you've got me wondering why it has to be so much more difficult in a boat motor.    Don't think I want to dig deep enough to find out the answer to that!

Of course what little knowledge I have of airplane engines derives from '30's, '40, and maybe '50's technology!

Hydrohokey, thanks for supplying the MAF translation.  I have 3 or 4 boater glossaries in my favorites list and still sometimes can't find the answer.  I'm still trying to figure out what a "beard line" is, also a "breakshear".

[hokeyhydro]

Shaking the dust bunnies off my ancient brain cells, I recall normally aspirated model airplane engines didn't seem to have a problem with altitude. Those engines were 2-stroke and ran on methanol & oil. Back in the 80s when I owned a hobby shop I witnessed two of our Washington D.C. area pilots duke it out for an altitude record at Dahlgren VA NAS. The winner went over 31,000 feet with his radio control plane. The radio Rx & battery pack had to be heated to work, but the glow ignition engine ran like a champ.

[Fishman38]

That's amazing!..............and brings up a lot of questions.  

[ecgossett]

The only problem I had with a 3.5 4hp Mercury Longshaft brand new at high altitude was it took a couple of extra cranks to start...

[rattus]

The Mass air flow sensor is part of a series of monitoring devices, to optimize the air fuel charge in the cylinders. Technically, the MAF senses volume, not density, but other devices in concert with the MAF can offset altitude changes. The engine still has to work with a decreased air density, but at least it can regulate the air/fuel mixture to compensate as much as practical.

 

...

 

Actually, a MAF sensor *does* sense density, in that it senses the cooling effect of flowing air (typically with the resistance of a wire) versus a reference "still air" wire. The cooling is brought on by flow rate * density - thus mass. At higher altitude, density is lower, the sensor gets cooled less, and it senses less mass. They're pretty accurate.

 

Edit: I meant hot film or wire.