Quote:
Originally Posted by Guran
Nice explanation of the dyno numbers, Adrian. Personally, when I look at those charts, the shape of the torque/tractive effort curve is what I'm most interested in. The absolute numbers are pretty meaningless unless you do the rough conversion that you've highlighted. Even then, it's still only a number. The torque curve tells you what you feel in the seat of your pants since torque is directly proportional to acceleration. If you have a flat torque curve, then you feel a constant surge of acceleration. But if you have a peaked torque curve, then you feel a sudden surge of acceleration as boost arrives, followed by an easing in acceleration as torque drops beyond the peak.
And there's lots more to this subject, such as losses in tractive effort caused by tyre pressures (generally higher pressures give better results), and losses due to centrifugal expansion of the tyre diameter at high speed (effectively alters the gearing).
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The shape of the torque curve gives the best indication of how a car will feel to drive as you say. I aim for a flat torque curve. It is actually not that hard to produce gobbs of torque down low, but unless you can maintain it up top, it ends up feeling flat... breathless. I like to see torque go to a peak as early as possible and then stay flat for 3-4000RPM before it drops off. This gives a nice linear feeling power curve. Additionally I like to see throttle control, so that even if you can produce high boost at low RPM, I want to be able to control how much boost I get with the accelerator pedal rather than just have it go straight to max boost making the pedal more like a switch.
Yes there is alot to dynos. They are best used for back to back comparisons for tuning or mods. This way the many non-linear variable remain as close as possible. It is hard to use them to compare different cars in different places. Expecially since different dyno types give different results. I have used them extensively throughout my work, so have done the research to know how to read dyno curves, but it is a shame most of the people who like to show off their dyno curves on forums do not understand them better.
The biggest misconception I see is that of power vs torque. Some people say they would rather tune for torque than power and do not realise that they are the same thing. They really mean they would prefer power at low RPm to power at high RPM.
Adrian