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      07-11-2013, 06:10 PM   #271
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Drives: BMW M2
Join Date: Aug 2012
Location: Bedford UK

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Originally Posted by swamp2 View Post
Nice charts. We should have been using these all along to discuss lag - a graph of torque vs. time due to step response on throttle. I've taken the liberty to add a typical NA response in purple and highlighting turbo lag in orange, it's probably more accurate to stick with it as a description simply as the time duration along the x-axis (rather than the highlighted area). Other than an exchange of power for torque this matches my first definition of turbo lag quite closely. However, to give one tiny concession to NISFAN, the case he likes to talk about would not have the NA and turbo torque asymptotes at the same level (and would then be headed right back to saying the NA engine has the lag...).

Also interesting are the double "kinks" in the blue curve which is what the prior poster was referring to in describing the electrical and computer controlled stuff as a bit artificial feeling (not sure if that was the exact term he used), which is indeed apparent in this system and you would feel this for sure and it would be a bit odd.
Swamp, this engine looks like a generator pack diesel. Note the increase in torque, but constant revs (almost). This can only be due to a load that increases with power output, like a generator set.

In any case the torque delay on the un assisted turbo doesn't make any sense. Lag that lasts for 4.5 seconds plus? No chance. More likely due to an uncontrolled wastegate, which starts boost leak very early, or other factors.

If it is indeed a generator set, the turbo system is matched so that at full power, the flow is exactly in the center island of the flow map (maximum efficiency island). In other words a very big turbo for the application. OK for static RPM/Load generators sets, no good for dynamic engines.

I am trying to find some graphs I had of Turbo response at different RPM WOT events. These clearly show high RPM response as being fractions of a second.