Review of HP and Torque
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Torque is a measurement of twisting force.
A 1 foot wrench with 1 pound of force pushing on the
end of the wrench is said to produce 1 foot-pounds of
torque.
There does not need to be motion to create torque,
unlike horsepower.
Torque is a SCALAR measurement, which means it has
magnitude only.
Electric motors can produce torque at zero rpm.
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Engines can’t because they won’t run at low rpm.
Review of HP and Torque
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Horsepower is a measure of work.
Horsepower can only be calculated after torque and
rpm are known.
Horsepower is a VECTOR measurement, meaning that
it has both magnitude and direction.
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Direction in this case is rotary.
If there is no motion, no work is done.
Because of this, the engine must be rotating to create
horsepower.
Review of HP and Torque
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Can be thought of as weight lifters.
‘A weightlifter can lift 400 lbs’
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All this tells us is that he can lift 400 lbs.
We don’t know how many times per minute he can lift this
much.
We can compare this to TORQUE.
‘A weightlifter can lift 400 lbs 5 times per minute’
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Not only does this tell us how much he can lift but how
much per minute.
We can compare this to horsepower.
Dynamometers
What is a dynamometer?
 On the most basic level, a dynamometer is a tool
for measuring the torque output and rpm of an
engine.
 Using the torque measurement and rpm the
dynamometer will automatically calculate
horsepower.
 Horsepower is not directly measurable.
 Horsepower = Torque x RPM / 5250
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Dynamometers
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Today’s dynamometers take a variety of
measurements.
Air/fuel ratio (AFR).
Air/fuel ratio is measured using a device calling
an air/fuel ratio analyzer.
A popular AFR analyzer is MoTeC’s PLM.
High end units are made by Horiba or Labcell.
Hobby level kits are made by various
manufacturers and are available by companies
such as Summit Racing.
Dynamometers
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The air/fuel ratio analyzer has a sensor, similar
to an O2 sensor, which is bolted into the
exhaust using a ‘bung’.
The sensor is called a UEGO (universal exhaust
gas oxygen) sensor.
Also known as a ‘Lambda’ sensor.
It is not the same as an oxygen sensor or
air/fuel ratio sensor found in a normal
passenger car or truck.
Dynamometers
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The high end air/fuel ratio analyzers use a
sensor which is very accurate and has a very high
sampling rate.
The ‘sampling rate’ is the speed at which the
measurements are updated.
Air/fuel ratio is defined as the ratio, by weight,
of air to fuel.
The stoichiometric ratio, also known as ‘stoich’,
is 14.7:1 for gasoline.
Dynamometers
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The stoichiometric ratio is that ratio at which
every molecule of air will chemically react with
every molecule of fuel.
In practice, this never happens – there are
always molecules that do not react and leave via
the tailpipe.
A 14.7:1 AFR would be 14.7 lbs of air to 1
pound of fuel.
Dynamometers
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An AFR less than 14.7:1 is considered ‘rich’.
This means that there is more fuel in the
mixture than is chemically correct.
For example, 12.5:1 AFR.
An AFR more than 14.7:1 is considered ‘lean’.
This means that there is less fuel in the mixture
than is chemically correct.
For example, 16:1 AFR.
Dynomometers
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Some tuners prefer to tune in ‘Lambda’.
Also known as the ‘excess air factor’.
In Lambda, stoich is represented by ‘1’.
Anything less than 1 is rich.
For example, .85 Lambda corresponds to a
12.5:1 AFR
A 1.1 Lambda corresponds to a 16:1 AFR.
Dynamometers
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Coolant temperature.
It is very important that the engine coolant
temperature be consistent from one dyno ‘pull’
to the next or readings could be inaccurate.
Exhaust temperature (using thermocouples).
A thermocouple is a device which plugs into
each individual exhaust port and measures
temperature.
Dynamometers
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By probing individual exhaust ports you can determine
if there is a problem in one cylinder. Or, on a
carbureted engine, you can determine if equal amounts
of fuel and air is being delivery to each cylinder.
Lean cylinders will have higher temperatures that rich
cylinders.
The extra fuel in a rich mixture causes combustion to
be cooler due to a phenomena called ‘latent heat of
vaporization’.
Dynamometers
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Brake specific fuel consumption (BSFC).
BSFC is a measure of fuel efficiency.
BSFC is the rate of fuel consumed divided by
the power produced.
BSFC is expressed in ‘pounds per horsepower
hour’ or lbs per hp/hr.
Dynamometers
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An efficient engine might be around .35 lbs per hp/hr.
An inefficient engine might be around .60 lbs per
hp/hr.
It is possible that both these engine make the same
amount of horsepower.
The engine with .35 lbs. per hp/hr would get
considerably better fuel consumption.
Fuel efficiency very important in endurance racing
(races lasting a long time – 4, 12, or 24 hours) for less
pit stops.
Dynamometers
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Intake air temperature.
The temperature of the air coming into the
engine.
Air temperature has a very large effect on power
output.
Colder air = more power.
Cold air is more dense and therefore contains
more oxygen per unit volume.
Dynamometers
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Ignition timing and advance curves.
Some dynamometers can track ignition timing
advance.
Some dynamometers have integrated detonation
detection equipment.
Dynamometers
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Ambient conditions.
Ambient temperature.
Humidity.
Barometric pressure.
Different brands of dynamometers have
different capabilities.
Dynamometers
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First dynamometer was called a prony brake.
Dynamometers
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Prony brake was made of wood and leather.
Wood block mechanism attached to ouput shaft
of engine.
Lever arm rests on a scale (like a bathroom
scale).
As engine is run, thumb screws are tightened
until rpm is steady.
Force on scale is read and rpm is recorded.
Very primative.
Dynamometers
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Different types of dynamometer mechanisms.
Type of dynamometer is determined by it
absorption unit.
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The absorption unit is what loads the engine.
Eddy current or electromagnet brake.
Hysteresis type is used for small engine dyno’s
(<200 HP).
Dynamometers
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Electric motor/generator type.
Has the ability to both load the engine and motor it.
 This can be useful for measuring the amount of
friction when the engine is motored.
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Hydraulic brake
Output shaft drives gear-drive pump
 Variable orifice on outside of the pump
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Dynamometers
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Water brake
Have high load capacity
 Low cost
 Uses something similar to a torque converter in an
automatic transmission to load the engine.
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Dynamometers
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Inertial Dynamometer.
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Dynojet Dyno’s, which are the most popular dynamometers,
are inertial.
Do not have the ability to load the engine.
Works by spinning a large, heavy drum.
Horsepower and torque are ‘interpolated’ by how fast it takes
to spin up the drum.
Readings are typically 10% higher than other dynamometers.
Many people use the term DHP (Dynojet horsepower)
instead of wheel horsepower.
They are inexpensive and therefore popular.
Dynamometers
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Different types of horsepower and torque
measurements.
Brake torque and means it was measured with a
dynamometer which has the ability to load the engine.
Torque is referred to as ‘Brake Torque’
BHP = ‘Brake Horsepower’
HP measured at the wheels on a chassis dyno is called
WHP or ‘Wheel Horsepower’.
Dynojet horsepower sometimes called ‘DHP’.
Dynamometers
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There are 2 basic types of dynamometers.
Engine dynamometer.
 Chassis dynamometer.
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An engine dynamometer tests the engine only.
A chassis dynamometer test the engine while it
is in the car, therefore it is also testing the
drivetrain.
Dynamometers
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Engine dynamometers.
Some common manufacturers.
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Superflow.
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Superflow was originally ‘Go Power Dyno’s’
First dyno was installed at Dema Elgins shop in Redwood City.
California Dynamometer was run for years out of Dema’s shop by
owner Gerard Rainey.
Shop has moved to San Carlos.
Superflow offers a wide variety of engine and chassis dynamometers.
Image of Dema Ferrari 206 engine on Superflow Dyno.
Dynamometers
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Some common manufacturers
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Mustang Dynamometer.
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Taylor Dynamometer
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Offers a complete line of engine and chassis dynamometers.
Eddy current type.
Hydraulic and eddy current types.
I don’t have experience with there but they look to be dynamometers
for large powerplants like diesel engines.
DTS (Dynamic Test Systems)
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Offers complete line of engine dynamometers.
Also sells valve spring dynamometers.
Recently merged with Superflow.
Dynamometers
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Parts of a dynamometer
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Test stand
This is what the engine is bolted to.
 Usually has wheels so engine can be removed from it
quickly and another engine put in its place.
 Engine dyno operators usually have multiple stands so
engines can be swapped out quickly.
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Dynamometers
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Cooling tower
Contains coolant hose connections that connect to
engine.
 Used instead of a radiator.
 Can be used to keep engine temperature constant
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This is important for getting consistent readings.
Absorption unit
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There are different types as mentioned earlier in
presentation.
Dynamometers
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Sensor box
Has leads for the different types of sensors.
 May have basic gauges on it also.
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Oil pressure.
 Coolant temperature.
 This is so if someone is in the dyno room they can keep
an eye on the vital basics.
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Throttle actuator
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Throttle is operated remotely.
Dynamometers
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Dyno room
Room contains dynamometer.
 Has provisions for supplying fresh air into room
 Has large exhaust fans for getting exhaust fumes out.
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Flexible exhaust tubes mount to exhaust.
Usually there is a tool box kept in room for working
on the engine.
Dynamometers
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Observation booth: Gerard Rainey
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Instruments
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Controls
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Torque
RPM (Tachometer)
Temeratures
Ambient conditions (weather)
Throttle
Load
Today’s dynamometers usually just have a computer instead of analog
instruments.
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However they still have mechanical controls for throttle and load.
Dynamometers
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Chassis dynamometers.
Some common manufacturers.
Superflow
 Mustang Dynamometers
 Dynapack
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Maker of hub mounted dynos
Dyno Dynamics
 Dynojet
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Not a true dynamometer, an inertial dynamometer.
Dynamometers
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Roller type
Drive wheels ride on a large textured drum which is
connected to the adsorption unit.
 Vehicle is tethered down with tie-straps.
 If tie-straps break, vehicle will launch.
 Variables need to be kept constant.
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Tire pressure.
 Strap tension.
 Sample video – Dynojet
 Sample video - Mustang
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Dynamometers
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Types of absorption units
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Same as with engine dynos
Depends on manufacturer
Exception is the Dynojet
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Uses an inertial drum
Large, heavy steel drum.
Vehicle is accelerated when on rollers
The time it takes to accelerate the drum is ‘interpolated’ into horsepower
and torque.
Can not load engine and hold rpm constant.
Readings are normally 10% higher than other dynos.
They are low cost, therefore very popular among the ‘tuner’ crowd.
Dynamometers
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Hub type
Bolts directly to hubs
 Can be used for 2 wheel drive or 4 wheel drive
 Eliminates variables associated with roller types.
 Are only a few manufacturers that currently make
them.
 Dynapack is the most popular.
 Sample video – dynapack.
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Dynamometers
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A dynamometer is only a tool.
A tool for verifying power goals have been met.
A tool for confirming that a modification has
made the increase in power which was
anticipated.
Results from one dyno should not be compared
with results from another dyno, especially of a
different brand.
Dynamometers
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Before and after test.
Vehicle or engine is tested before installing a
performance part.
 Vehicle is tested after performance part is installed
under same conditions.
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If weather is different results will be different even with
corrections.
A before test on a Dynojet and an after test on a
Mustang is invalid.
Dynamometers
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Before doing the dyno run.
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Temperatures must be stabilized to ensure
repeatability.
Coolant temp
 Engine oil temp
 Transmission oil temp
 Intake air temp
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Doing runs one after another is a good way to get
inconsistent results.
Dynamometers
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Cooling fan for chassis dyno
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Very important to have a very large fan in front of vehicle
during and after runs.
Most dyno operators do not own a proper fan.
Sample photo – small fan
Dinan has a 4 foot diameter fan with shrouding that narrows
down to about 1 foot by 2 feet.
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Has 40 HP electric motor
Can blow air at 80 MPH.
Large fan is especially important when testing cars with
intercoolers.
Dynamometers
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Corrections
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Since we can not control the weather, it is impossible to
ensure consistent conditions during dyno runs.
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Ambient temperature
Humidity
Barometric pressure.
Because of this, dynamometers have built in corrections
which adjust results to a standard.
SAE (Society of Automotive Engineers) standard J1349
Uncorrected
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People sometimes use to make it seem their engine made more power
than it did.
Do the run on a cold, dry day for maximum air density.
Dynamometers
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Dyno videos
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Cosworth 2.3 Liter
Mitsubishi Lancer
Lamborghini Gallardo
Renault F1
Dyno FAIL videos
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Mitsubishi EVO
Drag car
Unknown engine