# Maximum power piston engine

1. Dec 14, 2011

### oldboyonrgv

Is there any equation for calculating the maximum power possible for a given 4 stroke engine? per cylinder.
I guess it would involve:
Octain rating of fuel used
RPM
CC
some factor of bore X Stroke
And an efficiency of 100%!

2. Dec 14, 2011

### edgepflow

Yes, you can figure from brake specific fuel consumption, displacement, and volumetric efficiency. I have a book I will try to find and get back to you...

3. Dec 15, 2011

### edgepflow

OK, here is a simple approach for rough estimating. Actual engine power is based on many more variables that this method does not account for.

Lets try this for the new Boss 302 Mustang rated at 444 hp at 7400 rpm.

Compute the air flow rate at peak horsepower:

CFM = (VE)(CID)(RPM) / 3456 = (0.85)(302)(7400)/3456 = 550 cfm

A volumetric efficiency of 0.85 was assumed.

The mass flow rate of air:

mass_air = density X CFM = 0.076 lb / hr X 550 cfm = 2506 lb/hr

Now air and gasoline burn at a ratio of about 15:1, so the rate fuel is burned:

mass_fuel = mass_air / AF ratio = 2506 lb/hr / 15 = 186 lb/hr.

We convert the mass_fuel to power with "book value" of brake specific fuel consumption:

brake_hp = mass_fuel / bsfc = 186 lb/hr / 0.37 lb /hr-hp

brake_hp = 452

which is reasonable compared to published value of 444 hp.

4. Dec 15, 2011

### oldboyonrgv

Cool but I have some questions:
what is the 3456 number ? is it just a constant that should be used?
The book value is that a constant.......

5. Dec 15, 2011

### edgepflow

The 3456 number is a constant "conversion factor" to make all the units work.

And the book value can also be considered constant although bsfc for gasoline is a measured parameter and you will see some variation in the published values.

6. Dec 15, 2011

### pantaz

12 cubed (converting feet to inches), multiplied by 2 = 3456

7. Dec 16, 2011

### oldboyonrgv

OK thanks guys got it.