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View Full Version : Lb/min to CFM for air?

Unregistered
02-04-2006, 07:49 AM
I'm trying to convert air flow in pounds per minute to cubic feet per minute. Is there a conversion for this? It doesn't seem logical to be able to convert a flow density unit to a flow volume. Also, I've heard that there is a method of detemining horsepower in a car using CFM. The conversion factor I've been given is 1.6 CFM = 1hp. Wouldn't temperature have to be taken into consideration? I would think that a car ingesting 500 CFM at 50 deg. F would make more power than 500 CFM at 80 deg. F. It seems to me that a conversion from lb/min to hp would be more accurate, no? Thank you.

Todd

Robert Fogt
02-06-2006, 10:11 AM
The temperature definately needs taken into account.

I have density data for dry air at 0º C. I could create the conversion for that temperature, but for other temperatures I would need to know the density.

I think maybe the cooler the air the more it will expand when ignited with the fuel, giving more horsepower. Though being a computer nerd I've had little experience with automotive conversions. ;)

powerflowusa
02-16-2006, 06:53 PM
The temperature definitely needs taken into account.

I have density data for dry air at 0º C. I could create the conversion for that temperature, but for other temperatures I would need to know the density.

I think maybe the cooler the air the more it will expand when ignited with the fuel, giving more horsepower. Though being a computer nerd I've had little experience with automotive conversions. ;)

Yes this is true. HP is more based on the Fuel ratio and the Oxygen content, The cooler the air the more Oxygen molecules there are and more HP is produced. Same thing if you drive your car up in the mountains that's why cars feel like they make no power, Then you start changing things to compensate like the Pistons Compression Ratio will compensate across the board but there are many other things you can do too. Anyways.

Unregistered
03-30-2007, 04:07 PM
well a typical engine will make 9.5-10 hp per lb/min of air flow according to [..guest link posting not allowed..] they have all sorts of tech info like this on there. i would think you would have to find the mass of a particular volume of air (ex. cubic foot) at a certain temperature that you would normally operate your car in (ex. 70 deg.) and convert to find how many cubic feet of air at that temperature equals one pound. or vice versa.