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article details
Author WongKN
Categories General Information, All Honda/Acura, TOV World
Create Date May 02, 2002 00:00
Last Update May 13, 2002 14:53

How to Use a Dynojet

Modding our cars has now advanced to the stage where every serious modder realizes that proper dyno sessions are critical to getting the most power. This applies equally well to the professional mechanic as well as the hobbyist. Nevertheless, in my many interactions with fellow Honda enthusiasts and especially those who mods their cars, I was constantly surprised by the number who have not actually seen a dyno test in progress. Because of my good fortune in having witnessed numerous DynoJet sessions in detail, I thought it would be interesting to take a look and understand the DynoJet testing process.

I've written this article in a different format, relying on pictures and narratives as it is the clearest and most informative way to explain the dyno testing procedure. However, as with all other topics with Hondas, there are a lot of myths and misconceptions concerning the dyno process. To address a little of that, I added a section where I look at and discuss three of the more common misconceptions.

The Dynojet Procedure

A Dynojet measures power by measuring the acceleration of two huge drum's rotation. The basic procedure involves positioning the car's driving wheels so that when power is applied to them, they turn the Dynojet drums. Rate of rotation change is then used to calculate the amount of power being applied to the drums very accurately. This process is very simple and gives very consistent measurements. It is also now very clear why the Dynojet is said to measure your car's power at the wheels which should be the actual power we will be concerned about in the first place !

After visiting the Dynojet Far East office, I decided to follow the procedure as used by Dynojet Far East Sdn Bhd in this article. The pictures were taken over several separate dyno sessions.

1 The first step is to position your car so that the driving wheels rests on top of the dyno drums that is going to measure your car's power. The tyres should rest directly on top of the drums. However, if they don't rest exactly on top, do not get excited because fine adjustment will occur when they harness the car down later. It is also important that the car be pointing straight, ie both driving wheels are directly on top of the drums so that when power is applied, the car don't swerve around. A slanted position can also affect the accuracy of the dyno reading.

2 The bonnet is opened and a probe is attached to one of the spark plug leads to measure engine rpm. Because the Dynojet measures rpm by detecting the actual firing of the plugs (via electrical activity at the plug lead), it is very accurate and will often show if your car's tachometer is inaccurate. Similarly, rotation of the dyno drums will also show actual speed of the car at any time, again very accurately (the measurement is in feet per seconds). Thus, the accuracy of the car's speedometer can also be checked using a Dynojet !

3 The car is now harnessed down using special harness and securing hooks built into the testing floor. This will keep the car securely down when power is applied to the wheels otherwise the car might shoot off the dyno! For safety reasons, Dynojet Far East uses four harnesses, two each for the front and back of the car using the car's towing hooks. As an additional backup safety feature, Dynojet Far East also uses wheel wedges on the non-driving wheels.

4 The control box is now hooked up and the computer switched on. Air pressure is supplied to the control box in order to operate the air-brakes. The computer is usually permanently hooked up and just needs to be booted up. The Dynojet control program used to run on DOS but all current dyno jets will be using the newest Windows based versions called WINPEP. There is also a load-control program called DYNOTRAC which is a diagnosis tool. This allows the dyno to work in various modes, for example, keeping the 'speed' (ie rate of rotation of the wheels) of the car constant for all throttle positions in order to simulate lack of power during uphill climbs at low speed. Since the car is stationary during a dyno test, the engine can be studied to find out the cause of a problem.

5 The dyno fan is now carefully positioned. Dynojet Far East's procedure is to have the fan aimed at the air-filter or air-filter inlets and to direct airflow over the engine. The objective is to simulate an airflow equal to that generated when the car is travelling at low to moderate speeds. This fan is also critical when doing an extended dyno session because all engines will overheat when doing multiple consecutive full-throttle runs without proper air-flow to cool it.

6 The hand control (or control pendant) is made available to the driver who will do the actual dynoing (or dyno 'run') of the car. This box has two buttons, a red and a green. The red button activates the air-brakes to stop the drums while the green button when pressed will initiate the dyno measurement process.

7 Immediately before starting the dyno process, the car's particular will be keyed into the WINPEP program. Besides things like the owner's name and the car's registration plate number, other things includes the engine's configuration, like its red-line and spark-plug firing frequency measured in degrees of crank rotation, (eg B16A spark plugs will fire once per 720 degree of crank rotation).

The atmospheric conditions are the other crucial parameters for a dyno-run. In older dyno jets, the Dynojet operator has to measure parameters like air temperature manually. Dynojet Far East used to measure these using a digital meter. The values are measured once immediately before the start of the dyno-run and also re-measured again at various points in the case of a lengthy dyno-session. With the advent of the new Dynojet software/hardware, these parameters are now measured automatically by the system, once every 10 seconds !! All important atmospheric conditions; air temperature, pressure and humidity are measured by the control stack, shown at the photo on the left. The stack also forms part of the controlling hardware for DYNOTRAC.

8 Just before the dyno-runs proper starts, Dynojet Far East will check the tyre pressures to ensure they are at the proper levels. The car is now started and the engine allowed to warm up if necessary. The engine will then be revved several times primarily to allow the operators to tighten the harnesses properly. Thus the car is revved hard and the harnesses suitably tightened. When they are done, the car should be properly positioned on the drums and very securely fastened against it and the ground. Revving the engine will also help ensure that it is running at optimum.

When everything is properly set, the harnesses are re-checked once again for safety. Once done, the car is now tested to find the lowest starting rpm without the engine bogging down. As a guideline, Dynojet Far East works with an initial rpm derived as 1/3 of the engine's redline. Once this rpm is found, the green button on the hand control is pressed and the operator waits until rpm drops slightly below the starting rpm and then goes full-throttle until just after the redline.

9 The objective of all this effort - the actual dyno'ed power curve of the car at the wheels. Each new dynorun will be plotted together with the previous ones so after a number of consecutive runs, the chart becomes very congested and unwanted results will have to be deleted.

WINPEP will identify the maximum power and maximum torque by default, listing each run's respective values correlated by color. However it does not identify at what RPMs they occur at, the operator will have to identify that manually. It is also possible to pass the cursor over any part of the dyno chart and have WINPEP display the power/torque at that point. A typical dyno chart will plot power against rpm. If the torque is also displayed, it appears as a separate curve like in the photo on the left. If desired, the graph can be re-plotted against speed instead of rpm. This may be necessary in cases where the ignition cables are worn-out and the Dynojet probe will not be able to detect the spark firing pulses consistently.

The standard method of printing the dyno-run results is the graph as displayed by WINPEP. However, there is also an option to have the dyno-run results tabulated.

December 2000
© Temple of VTEC World
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