Not etirely correct. The change in pressure is largely due to the change in volume. The change in temperature is an adverse effect of this change in volume since the gas needs to exert work to expand, also known as the Joule Thompson Effect

Backpressure is actually reduced when you expand a gas into a larger space, think about it...would you rather blow through a drinking straw or a 3" pipe?

Temperature does not define the size of pipe used to transport gases, the limit is actually when the gas moves into critical (or choked) flow where the velocity of the gas becomes the speed of sound and the flow rate becomes independant of downstream pressure. A gas is a compressible fluid so is very felxible about the space it can fit in!

Economics come into play WAY before this critical point though, especially in a chemical plant. For choosing a pipe diameter in the processing industry we choose the optimum based on price to manufacture a pipe diameter versus acceptable system pressure loss from friction. We are also bound by acceptable velocities to ensure the pipe is not eroded.

The velocity increase can be best described by Bernoulli's Theorem

The effect on back pressure comes from the increase in frictional pressure loss (a resistance to flow!) due to the higher velocity of the gas.

As I said before in this thread, we don't break the rules of thermodynamics in Perth-WRX Nothing comes for free (especially energy!).

too much crack pipe ludwig

The Tomei 3" twin scroll dumps reduce in OD to gain power and torque they gradually step down from 75mm>70mm>65mm.

True - but the Torque scaling is the same on both graphs.

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MY09 Evo X - 1.6bar@3500rpm - got lag?
Barbagallo - 56.03 (S); 1:08.09 (L)
Collie - 50.77
Possibly the most under-driven Evo X in the world??

when you see the config on the dynapack for plotting the results, it makes sense-
the results can be made as smooth or as bumpy as you like, its the advantage of a hub dyno in that it is accurate enough to show these deviations, where a roller has no chance thanks to the inertia of the wheels/rollers.

horses for courses, remember dynos are a tool.

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Stace

Not that I wish to dwell on this, but my point still remains. How can you tell if the graph has more data points just by looking at the spacing on an axis? I assume that the dynapack allows you to set the min, max and spacing on an axis, or does it work these out based on the number of data points that you use? If that was the case then fair enough, but why wouldn't it do it over the rpm axis, as I assume that this is where you actually set your number of data points (i.e. sample every x rpm)

Intra is right, I guess it doesn't help that I've never used one.....

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John Stamos fan club lifetime member

the grid on the chart is irrelevant (its only there for reference), its the resolution of the datapoints that the graph plots over.

take a look at most plots, they are at 250rpm/20 or 10hp increments, but depending on the sample rate, the plot will either be smooth or shakey depending on the samples and time of the ramp for that power run. (quick ramp = fairly straight/smooth, slow ramp = much more data collected/more accurate)

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Long live the WRC

And can ramp rate be determined by looking at the graph, other than the "lumpiness" of it?

I'm just wondering how people can say that just because one plot is smoother than another means it has less data points, and is therefore a less accurate plot? As far as i can see, ramp rate is not listed on the dyno printout.

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John Stamos fan club lifetime member

its the sample rate mainly, check out this page for a bit more detail.

http://www.dynapackusa.com/tech.htm

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