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Understanding The Dyno
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In recent times there has been much confusion about dyno testing and what it means. There are many terms related to dyno testing, and some of these definitions can be confusing.
The term DYNO TESTING means that an engine is running under its own power coupled up to a controlled amount of resistance. The resistance is normally in the form of a water brake or an electric brake. The amount of resistance is typically measured in foot-pounds.
The term DYNO TUNED COMBINATION means that a particular combination of parts has been dyno tested in prior engines, and they are using this same combination of parts for other engines. If you buy an engine with a dyno tuned combination, it does not mean your particular engine has been dyno’d.
The term RUN IN has two different meanings. One means the engine is mounted with a driveshaft coupled to an electric motor, and the electric motor is spinning the crankshaft. This engine is not running on its own power.
The second one means the same as the term "HOT RUN", which is that the engine is bolted to a stand and is running under its own power, but there is no resistance being put against the engine.
When we dyno run an engine, we go through a lengthy procedure where the engine is first pre-lubed with the timing and carburetion roughly set. The engine is started and held at 2000 to 2,500 rpm’s for the first 15 minuets, but there is no resistance against the engine at this time. We then set the timing, and with the engine at operating temperature, we set the idle mixture screws and the resistance against the engine set at approximately 35 foot pounds. This simulates the engine idling in gear with an automatic transmission. We then go up and down the rpm range adding and subtracting the resistance, as this allows the rings to seat within the piston grooves. After a period of time, we apply more and more resistance which helps complete the break-in period. Now were ready to do a light power run up to 5,000 rpm. We double check the air fuel ratio, set the accelerator pump, and recheck the timing.
Now we’re ready to do one of three full power runs up to 6,000 rpm. Usually, when we do the second or third power run, the engine will pick up approximately 10 horsepower, due to the engine completing the break in process.