What’s in a Dyno Graph

Tow safely by understanding your dyno results

Words by Andrew Leimroth

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 motorhomes 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 vehicle’s 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 result graphs, meaning the first and fifth run may vary by as much as 10% if the engine started off testing cool and was running at normal operating temperature by the fifth. The old idea of paying for a ‘single power run’ may as well have been spent on something else.

So, my advice is to take the information and use it more as a guide to what your vehicle or motorhome 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 AFRs (air-fuel ratios) and turbo boost if the engine is turbocharged. 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, and this will show how ‘safe’ the results are.

Particularly on a diesel engine, the engine could 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 vehicle’s 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 motorhome is in the best condition to tow safely.

Safe Driving

Andrew