Dyno-mite Articles

 National Kart News

^THE
DYNAMOMETER

The ultimate tool?
By: Bob Chiras
With Input from Bob Bergeron, Land and Sea Inc. and Bill Price of Bill Price Racing

 There are a lot of issues that are discussed when it comes to dynamometers, and the answers provided could fill one of racings greatest joke books. Dynamometers are among the most misunderstood tools owned by the racers and engine builders.
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The frequently asked questions are:
Can I own a Dyno?
Should 1 own a Dyno?
How much money will I make if I buy a Dyno?
What can 1 Dyno to make money?
Will they pay me to run their motors on my Dyno at the track?
How much faster will a dyno make me go?
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    The answers are simple and complex in the same sentence. We will explore the uses of the dyno as a tool, opinions of some of the industries premier motor builders, and hear their and my answers to the frequently asked questions.

    A dynamometer is nothing more than a tool to deliver an effective comparison or analysis of an engine output or performance. Dynamometers are what is called a lagging indicator, that means that the dyno only tells you what has occurred during the dyno run or test period... After you have applied your best engine building skills, the dyno serves the purpose of evaluating the engine's capabilities at a given moment in time.

    So what does the typical dyno measure? Horse Power (typically at the crank shaft but in the case of a chassis dyno we measure HP at the rear axle), torque measured in foot pounds, RPM range over which the engine was tested, temperatures, air flow (volume and velocity of the air entering the engine), some measure noise levels of exhaust and intake manifold pressure, fuel flow, BSFC (the measured fuel flow in pounds per hour divided by the horsepower), and pressures such as oil pressure when appropriate.

    Dynamometers measure engine output; therefore, it's no surprise that top racers own a dyno. A dynamometer isolates and quantifies the metrics of horse power and torque...

    Racers understand that, without horsepower a kart goes nowhere. Like most test equipment, a dynamometer isolates and quantifies a particular metric (in this case the engine's output of horsepower and torque). Many modifications only help at specific RPMs, actually reducing performance at other points in the power band. With hours of track testing, you might condemn some new high rpm pipe as useless. How will you know if the modification only works with a dramatic jet change? Using a dynamometer helps you avoid discounting small gains from modifications. Just because you can't "feel" a power increase does not mean you want to forego ten such modifications. Combining small improvements is how championships are won...

    Because we are using a dynamic tool and we all know that weather and altitude all have an impact on performance, the Society of Automotive Engineers have developed mathematical formulas the allow us to correct any dyno run to provide a baseline comparison. A good dyno allows the user to enter today's environmental or altitude conditions. When reporting, the software provides the correction factors so that each day is measured as though it were the same as the last time that the engine was tested or to a set baseline so that you always achieve a set comparison.

    For years 1 have helped people who bought dynos. At best they got a very loose definition of a "build it yourself kit" where we spent hours chasing needed components, adapters, and the like from industrial supply houses to fabricating all kinds of plates brackets and stands. When we were done and ready to start testing the next big question we always faced was, "now what" as the instructions left us to figure out how and what to do and in what sequence. It was never a pleasant experience to have one of your motors on this concoction for the first few experiments.

    Back to the question: before you make the decision and convince the person in the house with the checkbook or credit card there are some factors to consider. The first is, can you really have a dyno at the location available to you? A Briggs at 7,000 RPMs, a Yamaha at 14,000 RPMs, or a shifter at 10000 RPMs does not go unnoticed by the neighbors. Sound deadening is only one of the issues, when you are running even small motors on the dyno the exhaust is still caustic and it will harm you in a poorly ventilated area.

    To get a great perspective on a well done setup, I traveled to Gilmanton Iron Works, New Hampshire and spent a day with Bill Price the owner of Bill Price Racing. He is one of the leading experts in the application of the Land and Sea DYNOmite Dyno for karting, and Bill has provided technical support to engine builders as far away as New Zealand.

    Bill shared information regarding different types of dynos. The simplest and earliest forms of dynos were brake dynos. They were just that, brakes. A rotating drum with a friction brake pad was used to apply drag at the engine's output shaft. These looked like old truck brakes. To measure torque, some sort of calibrated scale where the dyno's linkage was inserted at belt drive mates the brake pad anchor points to display the applied drag load.

    The DC generator dynamometer is a fancy way of saying that the generator's armature feels like a giant flywheel to the kart engine. High inertia means a lot of horsepower is required to accelerate the armature. Likewise, a lot of stored horsepower will be returned when dropping down in rpm.

    The Eddy current brakes are similar in operational characteristics to electric DC generator absorbers. The main difference is that the Eddy current brake does not actually generate electricity. Rather, the operator uses an electrical power supply to charge its electromagnetic coils. The brake's input shaft spins a metallic rotor inside that results in a magnetic field. When the dyno operator increases the current supply to the coils, the rotor shaft becomes harder for the test engine to turn.

    A more controllable load device is the hydraulic oil pump. These are occasionally seen on low rpm moderate horsepower engine dynamometers. A positive displacement oil pump acts as the brake and an adjustable oil discharge orifice valve sets the load. Like many absorbers, the oil pump units convert a test engine's power into a fluid's temperature rise. Since the oil can't be freely discharged, a cooling system (typically an oil to water heat exchanger) must be used to keep the oil's temperature within safe limits.

    Water brakes are another form of hydraulic pump absorber. These pumps typically have one or more veined rotors spinning in between pocketed stator housings. Load is controlled by varying the level of water in the brake with adjustable inlet and/or outlet orifices. Raising this water level increases the rotational drag of the pump's rotor thus applying more resistance to the engine turning it. Interestingly the water brake is, by design, a very inefficient pump. It uses up your engine's horsepower output by making "instant hot water"! Since the discharged hot water is clean, it can either be allowed to just run off, or it can be air cooled and recirculated.

    All of the above absorbers can be controlled manually by the operator (with a simple knob), or under computer control. Manual valve water brake load control is not as responsive as the electric DC generators or Eddy current controls, but with good electric servo valve controls you can close the gap a lot.

    Bill Price uses a Land and Sea Dyno, which is a computer controlled water brake.

    When we arrived at Bill's shop he had several motors available a 100CC JAKO, 100CC Comer, 100CC Yamaha, a 125 CC Yamaha Shifter and a 5 HP Briggs. Bill started his demonstration with a JACO, 100CC Two cycle motor run in the WKA Euro 5 class and Bill guided me through the controls of the computer and let me run the motor through its paces.

    The controls are impressive to say the least, and I spent most of the time watching the computer control the motor. We set the computer up to take 200 data samples per second. We told the computer the temperature, accurate relative humidity, and barometric pressure. We set the low limit where the data recording was to begin, and we set a high limit so that I could not over rev one of Bill's motors.

    In preparation for performing a dyno test there are certain metrics that you should have or should obtain prior to planning the test. These include the minimum horsepower, the gear ratio if you are not attaching the water break to the output shaft of the motor. With these metrics we will set up some basics in the dyno software. We want to see HP scales that start at about 20HP and above, as this is where we run the 125cc motor in the pictures. Gear ratios are key as they are factored into the calculations that determine torque, and if we do not factor the correct ratio we overstate or understate torque values.

    Other limits that were set included the number of spark pulses per revolution, specific gravity of the fuel, and finally a hold RPM (where we could bring the motor back to an idle and then let me repeat the run so that I could try to see all that was happening).

    Bill began my lessons concerning contemporary Dynos. Gone are the days of a giant setup, which occupied at least one half of a bay on anyone's shop. The Land and Sea DYNOmite occupied less room that is occupied by one half of a sprint kart.

    What was needed was a water supply, as the brake is a small water brake not larger than a dinner plate but about two inches thick, a waste water treatment process to deal with the warm water which is discharged, a secured mount for the torque arm and its deflection is the basis of the torque calculations, and some cables to attach the computer. Of course there are a lot of other attachments and options which really make the whole process more analytical.

    The most impressive part of the process was the data collected in a relatively short period of time. The dyno run was accomplished in seconds as opposed to the old process that was always measured in minutes.

    A second factor, which was impressive, was that we could do repeated runs and then have the computer report one run after another and the repeatability was superb. We could lay graph on top of graph and not see any differences that were greater than the width of a fine line.

    The answer to the question is that you can own a dyno. Make a list of the issues you have to consider and make sure that not only you but also the neighbors agree with your assessment.

    #1 Noise – Can you dissipate the noise of any motors that you run.
    #2 Exhaust – A two or 4 cycle motor will kill you as fast as your car. Even faster as a lot of racers are still using heavily leaded fuels.
    #3 Fuel – Motors require fuel, where can and will you store the race fuel. You cannot store the fuel in the basement of your home.
    #4 Space – Where are you going to set up so that you can be effective with the Dyno.
    #5 Cost – Dynos are a capital investment. How do you plan to recover your investment? Be realistic you are not going to have people sending you hundreds of motors a week to test without a great deal of accomplishments.
    #6 Airflow – Can you keep the airflow sufficient to keep the motors cool?
    #7 Water – Supply If you are on well water you need to verify that you have sufficient water volume for the water brake.
    #8 Do you have, or are you willing to get a PC and color printer? It is not a mandatory but it sure is nice to have.
    #9 Time – to get good with a dyno and to be able to make the small refinements which are necessary for national competition take time and dedication.
    #10 Disposition – do you have what it takes to be a successful motor builder? Dynos debunk all of the myths of what goes fast. Dynos tell the truth and when you find out all of the old wives tales do not change
the performance or degrade the performance it is a whole new day. Are you ready?
    #11 Your community – are the zoning regulations or fire regulations in your community going to allow you to operate the dyno. Make sure, I know professional motor builders who have lost leases because of Dynos.

    Contact others who have the dyno you are considering. Ask all of the tough questions: how long did it take you to get really set up for production work, how much did you really spend, who helped you? What lessons did you learn, and what did you break along the way? Would you do it again?

    Then achieve that dream that you can find the added performance and the combination that gives just that little bit more than all the rest.