Non engine related HP loss

[Texasmark]

Without regard to anything but the posted subjects, HP is reduced: by 3.5%/1000' of altitude and by 1% per 10*F of ambient temperature above 60F. Picked this up on the www on a petroleum site discussion.

What is needed to complete this is the relative humidity since (in my opinion) that has as much to do with loss as temperature.
So, when you folks post on here about your boat was running this way yesterday, and that way today with everything being the same, did you take ambient temp into account?

I was out the other morning and did a WOT run and was running 47. Couple of hours later did it again and was down to 45 and best I could tell nothing had changed with the boat and the only weather change (wind-waves) was that the air heated up and humidity lowered as it was slightly foggy and cooler on the first measurement.

 

[Mohawkmtrs]

You wrote about how altitude affects air pressure...does temperature and humidity affect air pressure as well?

 

[Old Ironmaker]

Both in my auto's and boat I always felt they ran best in the Fall when humidity dropped. More pep in the step as well as better fuel consumption. Hot humid summer days they ran like poo.

 

[Old Ironmaker]

You wrote about how altitude affects air pressure...does temperature and humidity affect air pressure as well?

I'm not sure he was talking about air pressure rather than available oxygen in the air. The higher altitude there is less O2 available. Where we are there is 21% O2 by volume of air, Denver has 18%. Turbo's and Superchargers force more air into the combustion chamber to get more oxygen in and the result is more HP. Once a certain elevation is reached you can't start a fire, not enough O2. Air with high humidity, water, inhibits good combustion resulting in poorer HP output, that's my theory I'm simplifying it. .

 

[Sprig]

Electronic fuel injection on modern vehicles/engines produces air/fuel ratios to compensate for air temp., humidity, and air pressure effects from weather and altitude. They work together with engine sensors and computers to give you optimum performance regardless of weather and altitude. Carbureted engines are for the most part unable to make such adjustments electronically.

 

[Old Ironmaker]

Electronic fuel injection on modern vehicles/engines produces air/fuel ratios to compensate for air temp., humidity, and air pressure effects from weather and altitude. They work together with engine sensors and computers to give you optimum performance regardless of weather and altitude. Carbureted engines are for the most part unable to make such adjustments electronically.

I agree EFI is great. Not all older engines such as my 94' Mariner have EFI, it's carbureted. But EFI can't create more oxygen in higher altitudes than what % is in the atmosphere. Adding nitros oxide will. I've yet to see a pleasure boat that has nitros oxide tanks. I bet there's some speed demons out there that have it.

 

[Texasmark]

I posted this because the subject comes up fairly often from high in the sky boaters and folks commenting that their boat isn't running like it did back......and were looking for something to fix. I couldn't help them as I didn't have the numbers and didn't feel like chasing after them at the time.

Air density has an effect and the more/denser the air, the bigger the bang....per turbo charger operating principle. Notice the cold air in a cold front comes in under hot air forcing it to rise (and in doing so helps to spawn tornados). 100% relative humidity air weighs more than 10% taking it to extremes. Turbochargers function is to pack more air into the combustion chamber, thus getting a denser concentration for a bigger bang. Where air molecules are far apart, like at altitude, turbos compress them into something more supportive of a good bang.

Side point. My tractors are naturally aspired. If I lived in Denver, they would be turbos for that reason.

 

[ahicks]

I can share that pilots flying small planes can tell you all about the effects of altitude and temperature, or they should be able to we'll say.

Humidity though, is not used to calculate take off distances (engine power), even though common sense would seem to tell you otherwise.

My own experience agrees. I have never seen evidence regarding the performance of anything when it comes to the effect humidity has on the way an engine runs. If you see a weather related difference, it about a temp change. When driving your car for instance, would you expect to see a difference in your gas mileage on a foggy, rainy 80 degree day vs. a hazy 80 degree day for instance? A crystal clear 80 degree day? That's me though, after a lifetime spent messing with engines. FWIW.

 

[JimS123]

Both in my auto's and boat I always felt they ran best in the Fall when humidity dropped. More pep in the step as well as better fuel consumption. Hot humid summer days they ran like poo.

Well, I never had an engine run like poo unless there was something wrong with it, and then it got to the doctor real quick.

However, years ago I DID notice poorer performance when the weather was hot and humid. Of course that was with old carbureated 2-strokes.

I have to say that my current EFI 4-strokes run the same all the time, and even under the worst conditions they out-perform a carbed 2-stroke. When you have a computer controlling the whole process it sure makes a difference.

 

[Old Ironmaker]

Well, I never had an engine run like poo unless there was something wrong with it, and then it got to the doctor real quick.
.

I'm talking British and German sports cars with dual or triple Stromberg carbs from the 60's and 70's that ran like poo .I had a 69' Mercedes 280 SE that had a carb the size of a toaster. Never could get it right. I swear I put more than a few mechanics kids through University back then. I was great at breaking things not so good at repairing them. They say they don't make things like they used to. Thank God they don't make engines the way they used to. I can truthfully say I can't complain about my 94' 115 HP Mariner, It never really ran poorly, it was more about water conditions.

 

[dwco5051]

Both in my auto's and boat I always felt they ran best in the Fall when humidity dropped. More pep in the step as well as better fuel consumption. Hot humid summer days they ran like poo.

You at least don't have to worry about loss of lift along with loss of power in a boat as you do in an aircraft when the density altitude is high. When some one complains about the air being "heavy" on a hot and humid day I am always tempted to correct them but know the explanation will take too long. Just remember that water vapor is 66% hydrogen and 33% oxygen and in a form that the oxygen can't help combustion and that air is usually 80% nitrogen and 20% oxygen that is usable.

 

[Texasmark]

I'm talking British and German sports cars with dual or triple Stromberg carbs from the 60's and 70's that ran like poo .I had a 69' Mercedes 280 SE that had a carb the size of a toaster. Never could get it right. I swear I put more than a few mechanics kids through University back then. I was great at breaking things not so good at repairing them. They say they don't make things like they used to. Thank God they don't make engines the way they used to. I can truthfully say I can't complain about my 94' 115 HP Mariner, It never really ran poorly, it was more about water conditions.

"I'm talking British..................." How about an MG "B" single seat roadster, bright yellow, tan leather seats, luggage rack on the "Boot", wire spoked wheels, Michelin Radials, I4 dual carbs.

 

[Scott Danforth]

you are all talking about the SAE HP corrections that must be taken into account when dyno testing anything and certifying it.

you want to make slightly more power, lower the incoming air temp to about 20F, drop the humidity to about 10% or less, drop the fuel temp to about 20F, and be at sea level on a high-pressure day. however we are only talking about a few % more power.

Agree with Jim, if the motor runs like poo, something is awry.

 

[ahicks]

"I'm talking British..................." How about an MG "B" single seat roadster, bright yellow, tan leather seats, luggage rack on the "Boot", wire spoked wheels, Michelin Radials, I4 dual carbs.

'67 Triumph GT6 w/leather, wire wheels, and an overdrive tranny that could be used to split each gear. When you first hear the tires starting to protest in a curve, you could make it going about 10mph faster without loosing it...... That car was a serious grin. There was also an Austin Healy Sprite, and an MGB. Thanks for the memories!

 

[Sea Rider]

Varying outside temp, pressure, humidity will make any motor to run slight less or slight more say on 2 consecutive morning runs while keeping same load equal.

Will disagree about modern EFI motors will adjust itself to perform top on high altitures. My EFI compact car turns into a pig starting 9 K Feet of elevation, the higher the worse due to less Oxygen availability. No EFI motor will make Oxygen out of its own to work same as when working at sea level conditions. Diesel motors performs much better at high altitude than gasoline powered motors..

Happy Boating

 

[Sprig]

EFI can’t produce oxygen but by adjusting the fuel/air mixture can greatly improve engine performance at altitude. It allows the max amount of O2 available into the engine. Carbureted can’t do the adjustments so you get the same air O2/fuel mixture at sea level as you do at say 8000’. Then you notice a huge reduction in performance. With EFI you may notice a reduction in performance at altitude but it’s slight compared to non EFI.

 

[Sea Rider]

Can greatly improved the performance is not the same as to equal the performance at sea level, for that must install a Oxygen cilinder system to increase the air mixture in the cylinder to match what's available at sea level. Some old radial motor airplanes used this sytem to cross high elevations. Sorry you can't add more of what's not already found there. 8 cylinder motors will lose less performance that 4 cylinder ones...

The only difference betwen a carbed and EFI motors going to high elevation is that on carbed motors need to manually increase the timing advance some + degreees while the EFI does it automatically. Have had both types working at high altitudes so can tell..

Happy Boating

 

[ahicks]

Timing change may be part of what an EFI system (fuelie) is capable of changing (maybe, not so sure there), but I can assure you that's not all that's happening. A MUCH bigger performance change is due to the fuelie's ability to lean the fuel mixture to compensate for the much lower percentages of oxygen available at altitude. A carbed engine at altitude is blubbery fat rich as it's still trying to consume all the fuel that's required at lower altitude (with much more oxygen available). Fuelies read barometric pressure AND temperature to allow them to compensate for changes required as each change.

 

[JimS123]

Will disagree about modern EFI motors will adjust itself to perform top on high altitures.

My comment about the superiority of computer controlled EFI was directed at temperature and humidity. I said nothing about altitude. That's a whole other ball-o-wax.

The bottom line is the O2 to fuel ratio. Obviously, nothing can manufacture O2, but a computer can certainly maintain the proper ratio. Adding an O2 system really ain't practical for everyman - unless your bizness is professional racing.

British cars......OMG. Back in college one of my classmates was a sports car nut. He and his father and uncle ran a sports car repair / detailing / restoration shop. He told me they wouldn't even let a brit on the property, much less work on one. But that's just him. I once drove an MG-B and I didn't want to do it a second time.

 

[Old Ironmaker]

"I'm talking British..................." How about an MG "B" single seat roadster, bright yellow, tan leather seats, luggage rack on the "Boot", wire spoked wheels, Michelin Radials, I4 dual carbs.

Don't forget the knock off wheel spinners. The best thing the Brits every came up with, in fact I think they stole it from us Italians. I had a 65 Triumph Bug Eye'd Sprite, 67 "B" and 72 TR-6. I never learned. The MGB and TR-6 actually had roll up windows. And I ran them in winter in Canada. I was always under the "bonnet" adding oil to the carbs.

Here's the GT6 in case no one ever saw one, very rare.

https://www.bing.com/images/search?q...+gt6&FORM=IGRE