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Misconceptions

At this point, I would like to briefly discuss three often misunderstood points about the dyno process.

1. The fan
As explained above, the fan is used to simulate an amount of air-flow equivalent to low to moderate speed against the front of the car. More importantly however, the air-flow also helps to cool the engine, to prevent it from over-heating. There have been a lot of debates on the perceived benefits of the fan's air-flow against an open engine bay, especially when the air-filter has been replaced by an open-element.

The Dynojet procedure do not recommend performing a dyno-run with the bonnet closed. As explained, this will quickly overheat the engine. Also results from various Hondata's HondaLogger captures I did on my car showed that the actual air temperature as measured by the ECU (via the temperature sensor mounted on the intake manifold runners) during dyno-runs are similar to that during normal road-use (in fact, in a couple of dyno-runs, air-temperatures at the end of the full-throttle run were in fact higher than those captured in full-throttle runs when driving in normal traffic on the roads !).

2. Correction for atmospheric conditions
WINPEP automatically corrects the results of a dyno-run to 'standard' atmospheric conditions (air temperature, pressure and humidity). This helps to allow different dyno-runs at different locations and different times to be compared against each other. Nevertheless, atmospheric conditions do impact the absolute power output of an engine. When two dyno-charts done during widely differing atmospheric conditions are brought up for comparison in WINPEP, the program will in fact issue a warning to that effect.

Another point to note is that immediately after a dyno-run, WINPEP will show the uncorrected power curve as the provisional result of the run. When the run result is saved to WINPEP and then brought up for examination, WINPEP will now show it corrected for the standard atmospheric condition.

3. The 'correct' number of runs
This is another point where a lot of confusion arises. When determining the power output of a car, the official Dynojet Far East procedure, which is adopted from guidelines from the Dynojet factory, is to perform dyno-runs until two consecutive runs produces the same results. Alternatives like performing a fixed set of dyno runs and then selecting the 'best' (ie the one with highest power) are not favoured. The Dynojet procedure ensures that we are measuring the consistent power output of the engine, ie the power we can depend on getting from the engine during normal driving conditions.

In addition, the official Dynojet procedure recommends that dyno-runs are performed in 3rd gear for 'smaller' engines, typically 2.0l and below and 4th gear for engines larger than 2.0l. For a particular car, dyno-runs are done using one gear only.


In this article, I took a look at the Dynojet dyno-testing process using the official Dynojet Far East procedure. Hopefully readers find this article interesting and useful when they eventually do their first dyno-test. I have also attempted to discuss some of the more important misconceptions and again I hope I have been successful in bringing out interesting perspectives on them.

WongKN
December 2000
Temple of VTEC World


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