Heat and Humidity vs Performance.

[Whitedog]

How much does high heat and humidity affect an outboard's performance in rpm loss or gain.

 

[cpj]

Re: Heat and Humidity vs Performance.

I would like to have that answered also.From my experince the other night,I lost about 1.5 mph when it was humid compared to when it was dry the time before.

 

[walleyehed]

Re: Heat and Humidity vs Performance.

95-100 deg day and high humidity, I lose about 300-400 RPM easy from running on a dry, 50 degree day with my 200 carbed Rude.<br />Seems like from 50 on down, there isn't as much gain. some are worse than others...depends how closely jetted a carbed engine is, and the EFI and DFI's aren't quite as bad, but still lose some performance.

 

[umblecumbuz]

Re: Heat and Humidity vs Performance.

Now that's strange.<br /><br />In the next factory unit to one we had before we moved, a firm was selling a water injector device for auto engines. Puts vapour into the inlet tract. Claimed it releases power, and it seemed to work. <br /><br />And when it rains, I swear my diesel motor goes better. <br /><br />Yet high humidity in two strokes seems to do the opposite.

 

[pine island fred]

Re: Heat and Humidity vs Performance.

Higher temps. will produce lower power output. An engine likes colder/denser air. As for humidity, dont quite know or remember. Older jets used water or water /alchoil injection to reduce egt. at take off power. Larger old radials used water injection called Anti-detonation injection. I am sure it works the same for 2 strokes. regards fred

 

[rodbolt]

Re: Heat and Humidity vs Performance.

think of it this way. in a cubic foot of air there is so much oxygen. about 20 percent. as the air temp increases the amount of oxygen in that cube diminishes. as the temp increases the amount of water vapor at a given temp increases. now we have even less oxygen. internal combustion engines like cool dense air. the humidity is not quite as critical as the air temp and the o2 density but anything that displaces o2 in our cube detracts from the power output. in measured quantities water caan turn to steam and assist in controling detonation. as the piston really does not care what pushes it down and water actually expands more than gasoline it can actually produce power as long as there is enough other fuel and o2 to sustain the correct combustion temps. similar to NO2. nitrogen is actually inert, the O2 molecules become seperated from the nitrogen during combustion. thats why ya have to add so much extra fuel or you lean out and almost instantly melt valves and pistons. ya outta see what happens on a 150 HP fogger at mid track when the fuel solinoid fails. gets a tad nasty.depending on altitude and temp you can lose 15% or so of the avalible HP at sealevel. thats why the top fuel people monitor barometric pressure, ambient air temps and relative humidity before adding nitro-methane. another oxygen bearing fuel.if not mixed correctly it goes lean and creates more problems. the leaner you can get it the faster you can go but if your a tad to lean its over. smoking metal

 

[pine island fred]

Re: Heat and Humidity vs Performance.

DAMN rodbolt, think you said it all. Would not suprise me if you didnt cut you teeth on old flat head FORDS. Ever run liquor? FRED p.s. believe water expands 36 times in volume when turned to steam at atmospheric pressure.

 

[CalicoKid]

Re: Heat and Humidity vs Performance.

Great explanation, thanks.

 

[rodbolt]

Re: Heat and Humidity vs Performance.

nope, I helped some buddies with some ford iron and some old hudson inline iron but I mainly stuck with chevy and olds. few pontiacs and buicks tossed in with the odd pakard and studebaker supercharged models tossed in just to aggrevate me. if ya really really want an exercise in frustration try to keep the electric torsion bar leveling system on a 56 clipper working . thats part of why I work on boats, more relaxing with less frustration . sometimes I think of getting back into hotrodding, lucky I am sober by morning and the thought has passed. but just for giggles how about this, a 330 olds forged crank, 350 olds heavy duty rods with a 403(4 5/16th bore) block with twin 500 CFM holleys and a w30 type cheater cam . or a lightly modified volvo 8.2 motor with an aftermarket adjustable EFI set up.the first would be a very short stroke large bore motor, should have very quick revs, the second would be expensive but could produce 600 HP with a smooth idle. gotta love smooth idle, even if ya have to do it at 100 RPM and slip the clutch at shut down, keeping it through the chevy HP 2.5" mufflers and full exhaust with balance tubes. keeps it quiet <br /> my 455 olds loved it .<br /> some of the kids with cameros and mustangs with glasspacks and big tires did not <br />but couple either the above with a 2500 pound body a nash 5 spd and 323 gears and you would have something that could stroll through the gears and still get groceries.