Ok who has the skinny on this question I have been given conflicting info on which is better in the marine environment. The humidity changes in Florida on summer nights are brutal on carbs you can really experience a drastic loss of power. I have been told that a m p f i unit will cure this so ok who knows has any one tried one out.
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MULTI PORT F I vs CARB
- Thread starter cntry141iq
- Start date
A
Anonymous
Guest
EFI makes broad power and better low end torque but believe it or not Carburetors make the most peak power. I’m a nut case I actualy carry a complete set of holley jet’s when I go riding/racing. Unless you are concerned about every single possible horsepower (like me) your jetting requirements will not change that rapidly. Humidity is a big factor but corrected altitude and air temp play the biggest roll. Corrected attitude, air coolness and humidity dictate how much oxygen is present in the air. Of the hundreds of aircraft guy’s I know I have not meet one that rejet’s from summer to winter. They generally think stock is always best. Generally in a day’s weather change you will not loose more than 15hp in a 400 inch air boat motor turn under 6,500 RPM’s. Now if you run a dual quad 700inch motor turning 9,500 RPM’s that’s a different story. The only major change will be if air temp drops and the air gets dryer, in this scenario you will make more power and even more if you rejet accordingly. Generally the later in the night it gets the cooler the air and this usually off set’s the humidity. Now another contributing factor over looked accept by pilots is when humidity increases the moister in the air will require more horsepower to turn a prop the same exact RPM. Humidity actually induces drag on a propeller. Thus magnifying what appears to be a horse power loss. Anyway I will always prefer a carb in a airboat because if you sink it just clean it out however if you have a DFI you will need to replace expensive parts. And my redneck ass can make a carb get me back in no matter what goes wrong with it. You can’t do that with a computer controlled fuel system unless you bring a spare of everything and your spare parts stay dry when you sink.
Waterthunder,
If the airplane engine guys are running the airplane carb, or the fuel injection for that matter, it has a mixture control in it. The airplanes need it to lean out at high altitude. So, the mixture would be infinitely adjustable from the drivers seat.
If an egt and a map are installed you could lean to the manufacturers specs for any given power setting. You could get max power at full power and max economy at cruise. You can approximate it without those gages, but it is not as accurate.
Jim
If the airplane engine guys are running the airplane carb, or the fuel injection for that matter, it has a mixture control in it. The airplanes need it to lean out at high altitude. So, the mixture would be infinitely adjustable from the drivers seat.
If an egt and a map are installed you could lean to the manufacturers specs for any given power setting. You could get max power at full power and max economy at cruise. You can approximate it without those gages, but it is not as accurate.
Jim
A
Anonymous
Guest
Planes must do that because the various altitudes they operate at. From see level up to ten thousand plus feet. If you can read a spark plug properly you can do the same thing as you mentioned with no cost and you don’t need to add any gadgets to your boat. Remember in an airboat you don’t change altitude more than ten feet unless of coarse you sink it. I have used the Bernstein race pack computer that utilzes digital thermal couples (digital EGT’s) in pro mod motors they cost a fortune and do not react to temperature quick enough to help tune any better than a magnifying glass and a good pair of eye’s. They use even slower working analog systems in planes because they run for long periods of time across a broad range of air conditions and you can’t shut off the motor to check you plugs for jetting conditions. Planes do not throttle up and down that much in flight these systems work great under a consistent load. However if you push the edge of performance and race around a lot they will not respond quick enough to do any good. I have melted 20 or so pistons before a thermal couple (EGT) even hinted there was a problem. Now if all you do is cruise around at a constant RPM for 15 minutes or more than you can take advantage of an EGT sensor and maximize fuel consumption.
My point was that the airplane motors can change the mixture for local conditions without changing jets.
There are digital systems available for aircraft that measure egt and cht for all cylinders, will alarm if a preset value is exceeded, and will record maximums. They are expensive, but so are engines. The digital data bus systems do all of that without the spiderweb of wires, but now you are talking big money.
edit
I think there may be better ones available now, but this one has been around since 1980 or so:
Jim
There are digital systems available for aircraft that measure egt and cht for all cylinders, will alarm if a preset value is exceeded, and will record maximums. They are expensive, but so are engines. The digital data bus systems do all of that without the spiderweb of wires, but now you are talking big money.
edit
I think there may be better ones available now, but this one has been around since 1980 or so:
Jim
WEll here is what happened ... It was a hot muggy summer night early in the evening just after dark ... I went to climb the dike at Okeechobee no one else was there thank goodness. My boat was lightly loaded but the humidity was 100% or felt like it anyways not a breathe of air movin on the lake I wanted some relief from the bugs while waitin on the frogs to come up and decided the place to wait it out was on top of the dike. I normally blow to the top no problem with 4 guys 3 coolers bait buckets and other odds and ends. This time just me and my lady 1 cooler no bait buckets and it barely made it up the dike had to turn off to the side pick up speed and then turn back up hill to get there. I had several people say a m p i would have corrected for the humidity and temperature and I would have no problems.. I agree sinkin a computer would not be a good idea and given the nature of airboats that is a real possibility. I probably will stay with the carb jsut because of the simplicity and reliability. Breakin out the laptop and runnin a diagnostic in a thunderstorm probably would cause a little tension. I already carry a spare hei distributor beacuse the msd box went out and stranded me once I dont need to carry a spare carb in case the puter goes out for the fuel system. THANKS GUYS I was just curious.