NZ Performance Car - - Contents - WORDS: JADEN MARTIN

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.

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