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has been replaced by an open-element.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
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
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