DYNO SHEET DECIPHER
WHAT ALL THOSE NUMBERS ON YOUR DYNO SHEET MEAN
So you’ve hit the dyno for a fresh tune and want to make sense of that weird-looking sheet handed to you? It may look quite complicated, but it’s actually relatively simple to understand once you know what you’re looking at. All the different dynos will give out different readings, so, for the sake of this article, we’re going to stick with a Dynapack for the sample. What most people don’t understand is that the dyno relies on a series of input values to calculate your power and torque figures. How these are entered can affect the result you will receive, which is what all that information on your dyno sheet is actually telling you. We teamed up with Jacky Tse of Jtune Automotive to give you a quick rundown on what each of these are.
This shows the torque curve over an X-axis (horizontal) of Newton metres (Nm) and Y-axis (vertical) of revolutions per minute (rpm). This figure is then outputted on the line below with the representative measurement, either in Nm or ft.lb.
This is the value difference between the plotted crosshair markers on the graph(s). It is typically used by the tuner as a comparison before and after a tune, or the difference between low- and high-boost power runs.
This shows the power curve over an X-axis of kilowatts (kW) and a Y-axis of rpm. This figure is then outputted on the line below with the representative measurement, either in kilowatts (kW), horsepower (hp), or pferdestärke (ps) — with 1kW being equal to 1.34hp and 1.36ps.
Created by the Society of Automotive Engineers (SAE), this is a correction factor that most don’t know about. Its purpose is to standardize correction values so that, regardless of whether a vehicle is tuned in Auckland, Christchurch, or Tokyo, the reading is the same or similar. The current gold standard is SAE J1349, enacted in 2004 — although you may find that some tuners use an adapted SAE to tweak certain correction factors. There are also STP and DIN, which are less common and will change the outputted power, generally making it higher.
This is known as the ‘transmission correction factor’. When the TCF is set to 1.000, power is being measured straight from the axles. To show power at the engine, a tuner can adjust this value to compensate for drivetrain loss. Every tuner will have different ideas on power lost for the vehicle’s specific set-up. Typically, four-wheel-drive vehicles will have a 10–15 per cent loss, which is represented by 1.10 or 1.15 TCF values.
This is the final-drive and gear ratio. For the dyno to calculate correctly what is being measured, the tuner needs to set the dyno rpm to match the gearing of the vehicle. For this example, the Honda Civic sampled has a 4.900 final-drive ratio, and, as the pull will be made in fourth gear, which has a 1.00 fourth-gear ratio, the ratio is inputted as 4.900:1. Changing this value incorrectly will alter the final power and torque reading; a higher ratio will result in more power shown.