Examining the dynamometer data
After you have performed your desired dynamometer tests, you need to take a look at the information you received.
If you have a manual recording system it’s time to take the calculator and extend the torque and rpm readings into horsepower numbers.
If you’ve got a manual electronic data collection it’s time to playback or print out the data. On personal computer equipped dynamometers you’ll usually want to name the new data file and probably enter any relevant engine data or special notations about the test run you have completed. There are software packages for your dynamometers that grant you the possibility of entering virtually any parameter you want in predefined windows. This is very handy, as you can store important information in a structured data base, making it more accessible. If your system is not equipped with sensors that automatically capture the weather conditions you should write them down as soon as you finish the dynamometer tests. It is very important to choose an appropriate output report format for reviewing the dynamometer’s data. When examining the data from you dyno, don’t rely on information captured during periods of rapid rpm change.
You should instead look for ranges (during the period of wide open throttle operation) where the engine maintains a steady rpm for a few consecutive seconds. When you examine the recorded data vs. time, it will be easier to spot the ranges where you held the rpm steady enough that your torque data is valid, and not influenced by crank-train inertia. Another important step is to average the data received from the dynamometer. Even numbers with a bit of inertial error can be averaged out to produce usable information. Computerized data acquisition systems allow you to set the averaging and dampening periods set to suit the type of testing you are doing. If something is obviously wrong with your results, like the rpm appears off by a factor of two, you might have selected the improper tachometer pulse setting. Or, if horsepower is only a fraction of what it was supposed to be, you should check if the throttle was wide open during the test.
Inexperienced dynamometer operators have a habit of backing the throttle, instead of cranking up the brake drag, when trying to regulate rpm. You should also remember about the problem of exhaust getting back into the intake system. Do a second pull, repeating the same procedures as the first dynamometer test, making sure you everything is checked and working properly. Remember to bring the engine back to some consistent temperature first. On the second run, you shouldn’t make any significant parameter changes, and concentrate on repeatability instead. In fact, you are really testing the repeatability of yourself and the engine, since the dynamometer does not change between runs. Whenever possible, especially when are chasing small improvements, retest the engine in its baseline form. This additional real-time check saves a lot of time in the long run.
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