Let have a technical discussion on optimum performance tuning for a N/A FE.

[jayb]

- I have an 8' X 10' room, with an 8' ceiling.  The room is at sea level, and 68 degrees Fahrenheit.  How much horsepower can I make with the air in the room in one minute?

No guesses?  The answer goes like this.  Density of air at sea level is .075 pounds per cubic foot.  There are 640 cubic feet of air in the room, so that means there are 48 pounds of air in the room.  An engine that uses1 pound of air per minute will generate 10 horsepower.  So, in one minute 48 pounds of air can make 480 horsepower, assuming the correct amount of fuel is added to the air.  The point here is that if too much or too little fuel is added, the engine will make less power, not more.  So the airflow through the engine is really what determines potential for power production.  This is why everybody focuses on flow for cylinder heads, intakes, etc., because that is where you can pick up power.

Here's another one.  For our engine that uses 48 pounds of air to make 480 horsepower in a minute, let's assume the engine is a 427 cubic inch FE operating at 100% volumetric efficiency.  What RPM will the engine be turning to make that horsepower?

[plovett]

- I have an 8' X 10' room, with an 8' ceiling.  The room is at sea level, and 68 degrees Fahrenheit.  How much horsepower can I make with the air in the room in one minute?

No guesses?  The answer goes like this.  Density of air at sea level is .075 pounds per cubic foot.  There are 640 cubic feet of air in the room, so that means there are 48 pounds of air in the room.  An engine that uses1 pound of air per minute will generate 10 horsepower.  So, in one minute 48 pounds of air can make 480 horsepower, assuming the correct amount of fuel is added to the air.  The point here is that if too much or too little fuel is added, the engine will make less power, not more.  So the airflow through the engine is really what determines potential for power production.  This is why everybody focuses on flow for cylinder heads, intakes, etc., because that is where you can pick up power.

Here's another one.  For our engine that uses 48 pounds of air to make 480 horsepower in a minute, let's assume the engine is a 427 cubic inch FE operating at 100% volumetric efficiency.  What RPM will the engine be turning to make that horsepower?

Jay, you sexy man!  I've decided you can have my daughter's hand in marriage.  I used to think you were a stranger, but now I feel like I've known you my whole life.   Forget about my daughter.  Marry ME!  Just keep talking about that air.

just sayin'

paulie

[69Cobra]

Ok if my math is right. There is 1,728 cubic inches in one cubic foot. 1728x640=1,105,920 Cubic inches of total volume. 1,105,920 / 427 = 2,589.97 x 4 = 10,359.90 RPM's???

[JamesonRacing]

Each cylinder takes in air every other revolution in a four-stroke engine, so I think you'd be at twice the RPM?  Doesn't seem right, must be missing something.....

[jayb]

Ok if my math is right. There is 1,728 cubic inches in one cubic foot. 1728x640=1,105,920 Cubic inches of total volume. 1,105,920 / 427 = 2,589.97 x 4 = 10,359.90 RPM's???

Pretty close, Kris, but I'm not sure where you got the additional multiplication factor of 4 in your answer.  The way I think of this is that it takes two revolutions of a four stroke engine to take in it's complete displacement.  So, for a 427" engine, for one complete revolution it will take in 427/2 cubic inches of air, or 213.5 cubic inches.  Using the numbers you calculated, 1,105,920 / 213.5 = 5180 RPM.

[jayb]

Jay, you sexy man!  I've decided you can have my daughter's hand in marriage.  I used to think you were a stranger, but now I feel like I've known you my whole life.   Forget about my daughter.  Marry ME!  Just keep talking about that air.

just sayin'

paulie

Geez Paulie, are you drinkin' again? Or just lonely or something?  

By the way, in the mountains at 6000 feet of elevation, our room contains on about 80% of the weight of air as it does at sea level, or 38.4 pounds, so our mythical 427 FE can only make 384 horsepower with that air in one minute.  Pretty big difference...

[69Cobra]

Ok if my math is right. There is 1,728 cubic inches in one cubic foot. 1728x640=1,105,920 Cubic inches of total volume. 1,105,920 / 427 = 2,589.97 x 4 = 10,359.90 RPM's???

Pretty close, Kris, but I'm not sure where you got the additional multiplication factor of 4 in your answer.  The way I think of this is that it takes two revolutions of a four stroke engine to take in it's complete displacement.  So, for a 427" engine, for one complete revolution it will take in 427/2 cubic inches of air, or 213.5 cubic inches.  Using the numbers you calculated, 1,105,920 / 213.5 = 5180 RPM.

Yeah I was just thinking 4 stroke but you are correct it only takes two revolutions to complete a cycle so it should've read 2,589.97 x 2 = 5,179.94

[Barry_R]

Don't give up on the fuel just yet.
Power comes from releasing the energy in the fuel.
Oxygen is the catalyst.
Not all fuels release the same BTU content once lit.
You are assuming that all of the oxygen comes from the air.

[plovett]

I don't know much about fuel, but I would say it's relatively easy to add more fuel, compared to adding more air.   

JMO,

paulie

[plovett]

Jay, you sexy man!  I've decided you can have my daughter's hand in marriage.  I used to think you were a stranger, but now I feel like I've known you my whole life.   Forget about my daughter.  Marry ME!  Just keep talking about that air.

just sayin'

paulie

Geez Paulie, are you drinkin' again? Or just lonely or something?  

By the way, in the mountains at 6000 feet of elevation, our room contains on about 80% of the weight of air as it does at sea level, or 38.4 pounds, so our mythical 427 FE can only make 384 horsepower with that air in one minute.  Pretty big difference...

I would say what we're basically talking about here is the "n" in PV=nRT.   n is more important than the volume of the room.  More n is more power potential, whether you look at it moles or mass or number of molecules.    Let's see, 38.4 pounds of air = about 150480 grams = about 519.4 moles = about 3.1 x 10E26 air molecules?    Well is that really helpful since air is made up of a mixture of different molecules?  Should we calculate the mass of just the oxygen molecules in our air?  What's equation for the reaction of air and fuel when it burns?  And all the gas will be expanding when it reacts, even the inert Nitrogen.   I need some more homebrew........

paulie

[plovett]

Oh yeah, how much water is in the room's air?   

paulie

[jayb]

Don't give up on the fuel just yet.
Power comes from releasing the energy in the fuel.
Oxygen is the catalyst.
Not all fuels release the same BTU content once lit.
You are assuming that all of the oxygen comes from the air.

Good point Barry, my example assumes a fuel that is non-oxygenated.  Fuels with ethanol or methanol, or nitro for that matter, will not follow those rules because they release oxygen during the burn, adding to the available oxygen for combustion.  A 10% ethanol fuel, like what you might get out of the pump, will be pretty close to the example given.  If I recall correctly methanol will be around 5% higher in power, and nitro will be WAY up there, like 2X the power. 

[jayb]

Oh yeah, how much water is in the room's air?   

paulie

My example assumed 0% humidity (even though I didn't say that  ).  Water in the air will displace oxygen, reducing power production.

[plovett]

What about water in the air allowing you to compress the air/fuel harder without preignition?  A small gain against a larger loss?

paulie

[jayb]

What about water in the air allowing you to compress the air/fuel harder without preignition?  A small gain against a larger loss?

paulie

Hmmmm, I don't know the answer to that one.  I assume you are correct that it would be a small gain against a larger loss, because if it wasn't, the car companies would be water injecting all their engines...