'IIIIMOIIETER BASICS

REVVING UP AND RECORDING THE .RESULTS IN PONIES Story and photos by Jimmie O'Dell

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

E ngine builders for years have secured their trust in a mechan­ical device called a dynamom­

eter 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 torque on the machine's frame. When a dynamometer is used to test engines, its reaction torque is used as a meas­ure of the tested powerplant's maxi­mum horsepower.

So, what actually is horsepower? The horsepower an engine produces is mea­sured by the rate at which it can per­form work. One horsepower is equiva­lent to lifting 33,000 pounds per foot in a minute. The horsepower developed by an engine depends upon the pres­sure exerted on the pistons by the expanding gases and the rate at which the power impulses are applied to the crankshaft.

The "brake" horsepower of an engine is the actual horsepower delivered from the crankshaft measured by means of an "engine" dynamometer. Bob Goshen of Bob Goshen Racing Engines con­ducts all his engine dyno testing aboard his 400 HP absorption brake dyna­mometer, manufactured by Stuska En­gineering Co. Kept cool by a high power fan blowing in cool air, the engine is mounted on a special dynamometer engine stand where the engine con-

nects up directly to the main shaft of the water brake reservoir.

The brake shaft contains a rotor in . the form of a paddle-like fan which rotates within an enclosed casing con­taining veins filled with water. The power of the engine is transmitted to the paddle rotor churning the water, thus putting a drag on the running engine. The dynamometer's water brake absorbs the power produced by the engine as it churns the water within the brake casing. The water would become extremely hot if left inside the water casing, so a continu­ous circulation of water is provided through an outside tap water source.

The enclosed casing tends to flex and twist in the same direction as the engine's rotation due to the torque, but this is prevented by means of a weighted pivotal arm. This pivotal arm connected to the water brake reservoir relays the leverage reading into tor­que pounds of pressure onto the oper­ator's control board.

A torque curve for a tested engine is obtained by the operator rotating 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 eval-

VW TRENDS/JANUARY 1991 35

D y N A M

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.

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

0 M E T E R B A s c s

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.

8. The engine's overall "chassis" dyno results of " net" horsepower and top MPH are displayed here on the Clayton Industries dyno digital readout. -

uations. For more information write or call Bob Goshen Racing Engines at 620 N. Berry St., Dept. VWT, Brea, CA 92621 (714) 990-2591.

The "net" or "as-installed" horse­power an engine develops can be re­presented on a "chassis" or "drive-on" dyno where the entire vehicle is driven on rollers, testing the engine's effi­ciency, performance, and road horse­power without ever removing the en­gine. The actual performance the en­gine creates is recorded with th'e fan, air filter, exhaust system, alternator, etc., all installed on the automobile. The final horsepower performance readings present a noticeable differ­ence when comparing figures between

. the engine dyno and the chassis dyno. In most comparison cases, the results are an approximate 20% power loss between the two types of dynos. This power loss is due to the additional drag on the engine from the transmission, fan, alternator, smog emissions system, etc. Automotive Performance Systems conducts tests on their Clayton C-796 "chassis" dyno, capable of recording up to 250 road horsepower. Aaron Neu­mann of APS uses the unit primarily for testing purposes, recording horse­power increases gained after installa­tion of their products on various water­cooled VW's.

The vehicle's total horsepower and 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 200-gallon 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. ~