AT 261 Engine Performance
Chapter 2 – Basic (And mostly true) Physics
Review.
•	Homework Review – 
•	Video Review – 
•	Lockers/Locks
•	Any Issues?
Physics of energy

Newton's Laws
•	1st law – Body in motion
–	Car coasting w/o power
•	2nd law – Acceleration is based on the power applied to an object
–	Applying more rotational force to the wheels from the engine
•	3rd law – Equal and Opposite reaction
–	Friction from road surface and wind drag
Where are the 3 laws?
3 Laws?
Physical laws
•	Work - is a byproduct of the force exerted on a mass to move it
•	Power - is work in a given time frame
•	Horsepower - is a given power over a given distance
•	Kinetic Energy - Energy in Motion (log rolling down a hill)
•	Potential Energy - Energy Stored (log still at top of hill)
Energy Conversion
•	Energy cannot be destroyed, only changed.
•	“Heat” is the ultimate result of energy.
•	Chemical = Gasoline
•	Burned = Heat/Motion
•	Motion = Alternator = Electrical
•	Electrical items put out heat.
•	What parts of a car “waste” heat?!
Automotive Physical Laws
•	Liquid is not compressible
•	A gas is compressible
•	“Air” is at 14.7 pounds per square inch
•	1” “square” 50 miles high = 14.7 pounds
•	Anything less than 14.7 is considered a vacuum

More Laws:
•	An object in motion will tend to stay in motion/rest – Inertia 
•	Friction - is heat, and sound given off by two objects rubbing against each other
•	Aerodynamics.
•	Which would be more efficient, based on wind resistance?

•	Mass and Weight - measurements that are used to determine the size of an object.  See side bar – pg 24
•	Volume - the amount of “space” an object takes up or can hold.

Torque
Break
Twisting Force..
•	Imagine that a wrench is placed on a bolt. The wrench has a 100-pound weight hanging on its end (Weight = 100 pounds). The distance from the centerline to the bolt to the end of the wrench is 1 foot. (Distance = 1 foot).
•	Because we know Torque = Distance x Weight (force applied), we know how much torque is being placed on the bolt:
•	So how many Ft/Lbs?

Power.
•	Horsepower is a measurement of torque
•	HP = (Torque x RPM)/5250

•	Which means, an engine that is putting out 200 Ft/Lbs at 5000 RPM… is putting out…  How much HP?
•	HP = (200x5000)/5250

•	Now if we are measuring torque and RPM how can we calculate horsepower? Where does the equation HP=TORQUE * RPM / 5252 come from? We will use Watts observation of one horsepower as 150 pounds, 220 feet in one minute. First we need express 150 pounds of force as foot pounds torque.

•	Pretend the force of 150 pounds is "applied" tangentially to a one foot radius circle. This would be 150 foot pounds torque.
•	Next we need to express 220 feet in one minute as RPM.
•	The circumference of a one foot radius circle is 6.283186 feet. ft. (Pi x diameter 3.141593 * 2 feet) 
•	The distance of 220 feet, divided by 6.283185 feet, gives us a RPM of 35.014. 
•	We are then talking about 150 pounds of force (150 foot pounds torque), 35 RPM, and one horsepower.
•	Constant (X) = 150 ft.lbs. * 35.014 RPM / 1hp
•	35.014 * 150 / 1 = 5252.1
•	5252 is the constant.
•	So then hp = torque * RPM / 5252

190.4761904761904761904 HP
•	Other ratings.
•	Watts = Heat output
•	KW = SAE term (1000 watts)
•	1 hp = 745.69987158227022 W 
•	Meaning a 115HP engine = 85755.48505 watts of energy 
•	Or 85.75 KW of power. 
Work it out…
•	How much HP for a engine?..
•	300 Ft/Lbs @ 3000 RPM
•	HP = (Torque x RPM)/5250
•	How many KWs?
•	1 hp = 745.69987158227022 W 

HP and Torque

Race them…
•	Torque is off the line winnings
•	VW Golf – 115 HP @ 5000 RPM
•	Honda Civic – 115 HP @ 6100 RPM
•	(yes, these are real numbers)
•	                     Horsepower * 5252
•	Torque  =     _______________
•	                               RPM

•	VW - ??

•	Honda - ??

•	Right?!

•	Who’s going to make the most torque in the 1st 50 (made up) feet?

•	VW  - 120 ft/Lbs, and the Honda makes 99.

•	Do it again..

There is…
•	Dynamometers can measure torque, in foot-pounds; they can NOT - directly measure horsepower. 
•	A long time ago, before any of us were born, James Watt performed some experiments and determined that a horse could lift 550 pounds at a rate of 1 foot per second. This unit of power, 550 foot-pounds per second, became known as the "Horsepower." 

So.. Why can’t we just go on for ever?
•	The reason is friction, of which there are three main sources: Aerodynamic drag, losses through the transmission, and tire friction. 
•	The loss from each of these sources increases geometrically with increased speed. 
•	Eventually, you reach a point where all the engine's power is being used to overcome these losses, so none is left over for acceleration. 
Horsepower to weight ratio:

Free “HP”.
•	Make car lighter
–	Spare tire
–	Seat
–	CF parts
•	Make it more aerodynamic
•	Reduce tire friction (higher pressures)
•	Reduce parasitic losses due to friction
–	Synthetic oils
Temperature;
•	More of “it” makes things expand
•	Less of “it” makes them shrink
•	More of “it” expands gasses
•	Less of “it” shrinks gasses (to the point of a solid..)
•	If we compress a “gas” the “gas” gains temperature
•	When we release the gas it looses temperature – Example!

Liquids
•	“Are not compressible” for us..
•	However….
•	You can compress water, or almost any material. However, it requires a great deal of pressure to accomplish a little compression. For that reason, liquids and solids are sometimes referred to as being incompressible. 
Atmospheric pressure
•	14.7 PSI @ Sea Level
•	Cooler air is more dense (more O2)
•	Pressure and Altitude
•	Higher up = Less pressure = Less O2
•	Author’s Note? – Lets read it…
•	http://www.csgnetwork.com/h2oboil2calc.html/

•	If the temperature of the boiling water on the mountaintop is 185 degrees Fahrenheit, then the time taken to cook the egg will have to INCREASE to get our hardboiled egg. 
•	It is no different to cooking a piece of steak or cooking the potatoes. You can cook at a low temperature for a long time, or a high temperature for a short time

•	It is time and temperature that does the cooking. 
•	It has nothing to do with whether the water is boiling. 
•	That is only a physical phenomenon that you can see. 
•	You have to measure for temperature and time, as these are the two factors that determine when the egg is hardboiled.
Vacuum Scale
•	Take a look at chart – 2-17 pg 32
•	Hg = Mercury
•	Think of a long tube sucking a metal up into it…..
•	Engines run at (idle) at 18-22” Hg
•	30” Hg = Total vacuum (for us)
•	0” Hg = 14.7 PSI = 0 PSIG (gauge)

HOMEWORK!

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