What's in a Dyno graph?

You’ve had it all checked and graphed but “what really’ is in a Dyno graph”? More importantly “what
should you be demanding” on the report. Dyno graphs are still probably the most misrepresented
piece of paper received by a Vehicle owner.

The most common Dyno used to date for cars, 4WDs and Motor homes would be a wheel roller
Dyno. Simply put the vehicle is driven onto the Dyno for testing. The steel rollers of the Dyno that
the vehicles tyres will turn generally have a large magnet attached to them. Electric current is sent to
them to prevent the wheels from accelerating away and is converted by the Dyno computer to read
a Power and Torque figure on the screen.

This information will vary from Dyno to Dyno due to various conditions including atmospheric
conditions. Any good dyno operator will do multiple runs to gain a repeatable average of the dyno
result graphs. Meaning the first and 5 th run may vary as much as 10% if the engine started off testing
cool and was by the 5 th run well at operating temperature. The old idea of paying for a ‘single power
run’ may as well have been spent on a something else. So my advice is to take the information and
use it more as a guide to what your vehicle or Motor home obtained on that day. The Dyno operator
should explain the results to you. If you have just had the engine tuned you should be able to see
some power gains as well.

Some other very important information rarely included in results is exhaust gas AFR (Air Fuel Ratios)
and Turbo boost if the engine is turbo charged. The actual power results are pretty useless if the
power gained was through incorrect tuning. The AFR reading will show you how ‘rich or lean’ the
mixture is. This will show how ‘safe’ the results are. Particularly on a Diesel engine the engine may
have been tuned up 20% BUT may have had the fuel loadings increased substantially to do this.

Seeing the AFR graph under the power graphs will confirm if the power gain was obtained without
turning up the fuel too much (remembering Fuel makes heat in a Diesel). So many times I see what is
excessive overpowering due to over-fuelling in a Diesel. The Dyno graphs looked great until the AFR
reading is taken only to show worrying over-fuelling.

Turbo boost being graphed as well will make sure that the boost isn’t slow in responding or too high
for sustained reliability.

The key to your vehicles Dyno result is understanding the graphs and figures. Make sure you ask
questions and feel comfortable with the explanations and through this you will be sure that your
tow vehicle or Motor home is in the best condition to tow safely.