Math Quiz for a Math Wiz


How many gallons of air per hour are used in an engine with the following parameters?

710 cubic inch displacement x 12 cylinders = 8520 cid

800 rpm x 60 minutes = 48,000 rph

Airbox pressure = 28-32 psi (almost 2 atmospheres)

Airbox temperature 110 degrees F

Trying to convert cubic inches to cubic feet to gallons
I came up with over 3.5 million, is this even close?


I have no idea. But there are 231 cubic inches in a U.S. gallon. Now, excuse my limited engine experience, but if it is a 4 stroke you are only drawing air on one stroke so it would take two revolutions to complete one “inhalation” for each cylinder for your calculations?

A gallon of air is a gallon of air at 23 psi or 230 psi. If you are looking to find the gallons of air at sea level pressure then there is some more ciphering you gots to do. [B]ft<SUP>3</SUP> / hr = ( lbs / hr ) / ( lbs / ft<SUP>3</SUP> )[/B]
so you would get your cubic feet per hour = by dividing the weight (density) of the compressed gas at it’s temperature /by the weight (density) of the air at 1 atmosphere at your reference temperature or what ever reference you wanted. Do all that and convert to gallons per hour. 7.48 gallons in 1 cubic foot.

Probably cause you to have more questions, but this should get you close. Depends on whether you are trying to win a bar bet or get your PHD. My internet signal won’t hold out long enough to get you any more info. Post back what you find. Inquiring minds want to know.

And remember there are no stupid questions, but there are a lot of inquisitive idiots! (Please don’t take offense to that as it just my sense of humor, I would certainly be one of the later).

Good luck and cut me in on the profits is this was a bar bet.



[QUOTE=seadog!;31639]How many gallons of air per hour are used in an engine with the following parameters?[/QUOTE]
My question is…Why GPH??


I was hoping you’d weigh in.

GPH to be able to compare with fuel GPH. As in: For every gallon of fuel burned, X gallons of air are consumed, or: we burn 150 gallons of fuel per hour and 1.75 million gallons of air.

I think a gallon of air being a gallon of air only applies after that gallon has been pressurized, a gallon of air at 2 atmospheres should be 2 gallons if allowed to expand. It would be twice as dense.


I’m still trying to figure why you’re calculating air flow in gallons. The CID of the engine is only a partial requirement for calculating ventilation. EMDs use much more air in the scavenging process than piston displacement. The older medium speed direct reversible 2 cycle engines (Bronz) needed pressurized engine rooms for reliable starting and slow bell operations. Air change requirements have increased with electronic controls and oil mist detectors. Many variables to consider…


If you really want to get exact you’ll have to look at the temperature of the air post supercharging. Easiest way to take that into accont is using the ideal gas law. A gallon of hot air will have less air molecules then a gallon of cold air.


You’re right about the cycles. (Although this is a 2-stroke)[/QUOTE]

2-Stroke was my nickname in high school.


My wife still calls me that.

She said she was looking forward to some good hot sex, and would I stay at sea a little longer until she had a chance to get some.