VW Trends January 1991

'IIIIMOIIETER
BASICS
REVVING UP AND RECORDING THE .RESULTS IN PONIES
Story and photos by Jimmie O'Dell
E
1. Bob Goshen's "brake" absorption engine dynamometer Is capable of handling up to 400 HP.
The air-cooled VW is mounted-up and ready for a test session inside Bob's shop.
34
VW TRENDS/JANUARY 1991
ngine builders for years have
secured their trust in a mechanical device called a dynamometer when building and testing their
automotive powerplants. A dynamometez: is a device with a rotating shaft
coupled up to the drive shaft of the
engine or machine being tested. This
device measures the mechanical power
output and the driving torque of the
engine. This torque figure measured
by the dynamometer is calculated with
the shaft's velocity which is measured
by the tachometer, thus arriving with
an overall computed horsepower for the
tested machine.
The principle operation of a dynamometer is based on Newton's third
law of motion, which states that the
forces of action and reaction are equal
and coexistent. In engines and generators, for example, the torque developed
by the armature current ofthe machine
2. The mounted In the floor "chassis" dyno at Automotive
Performance Systems Is capable of recording up to 250 HP produced
from a vehicle's drive wheels.
3. The engine dyno master control board features a torque gauge
(center), fuel flow meter (top right), air density gauge (top center) and
the load dial (far left).
exerts an equal and opposite reaction nects up directly to the main shaft of
torque on the machine's frame. When the water brake reservoir.
a dynamometer is used to test engines,
The brake shaft contains a rotor in
its reaction torque is used as a meas- . the form of a paddle-like fan which
ure of the tested powerplant's maxi- rotates within an enclosed casing conmum horsepower.
taining veins filled with water. The
So, what actually is horsepower? The power of the engine is transmitted to
horsepower an engine produces is mea- the paddle rotor churning the water,
sured by the rate at which it can per- thus putting a drag on the running
form work. One horsepower is equiva- engine. The dynamometer's water
lent to lifting 33,000 pounds per foot brake absorbs the power produced by
in a minute. The horsepower developed the engine as it churns the water
by an engine depends upon the pres- within the brake casing. The water
sure exerted on the pistons by the would become extremely hot if left
expanding gases and the rate at which inside the water casing, so a continuthe power impulses are applied to the ous circulation of water is provided
crankshaft.
through an outside tap water source.
The "brake" horsepower of an engine
The enclosed casing tends to flex
is the actual horsepower delivered from and twist in the same direction as the
the crankshaft measured by means of engine's rotation due to the torque,
an "engine" dynamometer. Bob Goshen but this is prevented by means of a
of Bob Goshen Racing Engines con- weighted pivotal arm. This pivotal arm
ducts all his engine dyno testing aboard connected to the water brake reservoir
his 400 HP absorption brake dyna- relays the leverage reading into tormometer, manufactured by Stuska En- que pounds of pressure onto the opergineering Co. Kept cool by a high power ator's control board.
A torque curve for a tested engine
fan blowing in cool air, the engine is
mounted on a special dynamometer is obtained by the operator rotating
engine stand where the engine con- the dial located on the master control
board for a specific ~mount of load,
all while controlling .the running engine in the full-throtf!e position. The
load is adjusted and applied to the
engine with the torque figures registered and recorded on the torque scale
at various RPM levels ranging from
2000 RPM to 10,000 RPM, depending
upon the desired purpose the engine
was built.
Beyond looking for high horsepower
numbers, renown -off-road VW race
engine builder Bob Goshen, tests and
evaluates all of his race engines that
receive his personal horsepower improving modifications. When testing on
an engine dynamometer, only the
engine's essential driven equipment is
installed. Most engine builders opt to
retain the air filter and exhaust system to simulate a specific race environment during testing. Bob also
evaluates carburetor jetting, testing the
engine for the appropriate jetting combination that will be best suited for
a specific race track's demands. Bob
Goshen Racing works on an appointment only basis for performance VW
race engine building and dyno evalVW TRENDS/JANUARY 1991 35
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7. ABOVE - Aaron Neumann of APS logs in
the engine's performance figures during a test
on tneir " chassis" dyno. The dyno's load and
brake are controlled from a remote inside the
vehicle.
6.
LEFT - Once the vehicle is loaded onto
the rollers, the center support is dropped away
beneath the wheels, the engine is revved, and
load is applied to the rotating rollers.
4.
The large black circular shaped housing is
the water absorption brake. A paddle-/Ike fan,
connected to the engine, churns the water
enclosed Inside the housing.
8. The engine's overall "chassis" dyno results of " net" horsepower and top MPH
here on the Clayton Industries dyno digital readout.
5. Bob Goshen rev.s an engine up on his
dyno, controlling the load with one hand and
the engine's throttle with the other, as he
searches for the optimum horsepower.
36
VW TRENDS / JANUARY 1991
are displayed
uations. For more information write or . the engine dyno and the chassis dyno.
call Bob Goshen Racing Engines at 620 In most comparison cases, the results
N. Berry St., Dept. VWT, Brea, CA are an approximate 20% power loss
92621 (714) 990-2591.
between the two types of dynos. This
The " net" or "as-installed" horse- power loss is due to the additional drag
power an engine develops can be re- on the engine from the transmission,
presented on a "chassis" or "drive-on" fan, alternator, smog emissions system,
dyno where the entire vehicle is driven etc. Automotive Performance Systems
on rollers, testing the engine's effi- conducts tests on their Clayton C-796
ciency, performance, and road horse- "chassis" dyno, capable of recording up
power without ever removing the en- to 250 road horsepower. Aaron Neugine. The actual performance the en- mann of APS uses the unit primarily
gine creates is recorded with th'e fan, for testing purposes, recording horseair filter, exhaust system, alternator, power increases gained after installaetc., all installed on the automobile. tion of their products on various waterThe final horsepower performance cooled VW's.
readings present a noticeable differThe vehicle's total horsepower and
ence when comparing figures between
Continued on page 82
DYNAMOMETER
BASICS
Continued from page 36
top speed output is measured through
the rotation of two driven rollers. The
vehicle's drive wheels (whether it be
front or rear wheel driven) are driven
onto a roller assembly located in the
floor. A remote control module operated by the technician lowers the center
support between the rollers hydraulically, with the two rollers cradling the
auto's two drive wheels. While a high
powered fan blows cool air onto the
engine, torque is applied to the wheels
revolving the rollers connected to the
power absorption unit (PAU) and the
load to the engine is applied. The
remote controlled absorption unit dissipates the power the vehicle produces
by controlling the flow of water within
the unit's rotor and stator assembly.
Resistance or "load" is created according to the flow of water and electrical
current fed through the assembly. The
unit's water is stored below the dyno
underground inside the huge 200gallon water storage tank.
The " net" horsepower and miles per
hour figures obtained on the chassis
dyno are displayed on a remote digital
readout panel. APS presently schedules dyno testing on their "chassis"
dyno for water-cooled customers on an
appointment only basis, with testing
prices starting around $65 . Automotive Performance Systems can be contacted at 1464 North Hundley St.,
Anaheim, CA 92806. Or give them a
call at (714) 630-1144.
Bob Goshen of Bob Goshen Racing
recommends a few valuable accessory
instruments for use when testing on
the dynamometer. The first instrument he advises for use, is an accurate
fuel flow rate meter. Bob personally
uses a device manufactured by Stuska
Engineering Co. when conducting tests
on his dyno. The fuel flow rate meter
is capable of obtai~ing instantaneous
fuel flow rates at any RPM or throttle
condition.
The calculated "brake fuel consumption" (B.S.F.C.) is measured by this
unit, displaying the engine's overall
efficiency. The instrument reads on a
ten inch scale, in increments of pounds
of fuel supplied per hour. The fuel flow
rate meter also proves invaluable when
testing an engine on the dyno to determine proper carburetor jet sizes, injection pressures and orifice sizes. The
finai air-fuel ratio of an engine can be
adjusted on the dyno for the particular
intended use of the engine. For in-
stance, competition engine fuel ratios
are usually set for maximum torque
throughout the RPM range, thus, saving hours of unnecessary testing at
the track on race day.
Bob Goshen says of his second recommended item, "I can't accentuate
enough, on how necessary an air density gauge is for the racer and engine
builder to use". Outside elements such
as altitude, temperature and humidity
all play a big role in the engine's
capabilities of producing optimum
horsepower figures. The gauge can be
used to record the air density at the
time of dyno testing, when optimum
horsepower was produced, and then
again for recording the air density at
the track. If any change is detected,
the engine builder has the opportunity
to correct the amount of fuel to be
added-to or subtracted-from the carburetor, insuring the engine the optimum
air fuel mixture, just as it was tested
in the dyno. An engine's best power
is obtained through using just the right
fuel mixture; too rich or too lean will
produce less overall power. Neither
fuel injection, nor carburetors have
the automatic capabilities to change
the amount of fuel that they meter
into the engine when the air density
changes. The gauge manufactured by
Kinsler Fuel Injection, is simply a
small metal bellows with some air
sealed inside. When the atmospheric
pressure rises, the belows compresses,
moving the needle on the face of the
gauge higher.
Each time your piston goes down, it
sucks in the same volume of air, the
weight of that volume will vary from
day to day. When the temperature cools,
the air shrinks slightly; making it
denser. The cooler temperatures will
also shrink the air contained inside
the air density gauge belows, pulling
the sides together and moving the needle higher. The gauge will give one
needle reading showing the net affect
of the atmospheric pressure and temperature on the air density.
If the atmospheric pressure increases,
a high barometer reading results and
the air becomes compressed slightly,
becoming denser. When the air density
increase, it is necessary to increase
the fuel mixture because the same
volume of air weighs more. If the fuel
mixture is not increased, a substantial
power loss will occur due to the extremely lean conditions, which could
result in damage to the engine. This
gauge will prove itself invaluable when
used correctly with the dyno and at
the track.
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