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    • The difference density altitude makes - 60-130 Testing in +2000 DA vs. -700 DA

      This video really can be summed up in one screen grab but the guy sure loves to hear himself talk. The car you are familiar with as it is the ES750RS Porsche 991.1 Turbo S recently written about which has factory GT2 RS VTG turbochargers.


      It's a quick car and a good test bed for how much a 60-130 mph sprint can sway in different DA (density altitude).

      This is important to note as the problem with times is they vary. They are fluid. They are not static yet you will notice that forum racers will always choose the quickest time or comparison purposes rather than the average time.

      A guy will cherry pick a run from ATCO in -3000 DA and then wonder why another car in Arizona in 90 degree weather is more than a second off.

      This is a difference of roughly 2700 feet yet it affects the 60-130 sprint by almost 4/10's of a second:


      The larger the DA disparity the larger the difference. A 2700 foot spread is not even that large considering how elevation and weather changes across the USA let alone the globe.

      There is a reason the quickest and fastest times all come from ATCO (or MIR) in the winter. That reason is DA.


      This article was originally published in forum thread: The difference density altitude makes - 60-130 Testing in +2000 DA vs. -700 DA started by Sticky View original post
      Comments 15 Comments
      1. Stevenh's Avatar
        Stevenh -
        A. Double check your math.

        B. 2,000 DA?! Sounds like a nice day to get to the track!
      1. Sticky2's Avatar
        Sticky2 -
        Click here to enlarge Originally Posted by Stevenh Click here to enlarge
        A. Double check your math.

        B. 2,000 DA?! Sounds like a nice day to get to the track!
        2700 I mean...
      1. Markblackwell's Avatar
        Markblackwell -
        It was interesting but, One was done from a roll the other was done from a dig as well so there’s that.
      1. Sticky2's Avatar
        Sticky2 -
        Click here to enlarge Originally Posted by Markblackwell Click here to enlarge
        It was interesting but, One was done from a roll the other was done from a dig as well so there’s that.
        A fair point as well
      1. F16HTON's Avatar
        F16HTON -
        The acceleration(g) slope is the differentiation, not the DA. You can clearly see the shifts in the slower pull.
      1. Sticky2's Avatar
        Sticky2 -
        Click here to enlarge Originally Posted by F16HTON Click here to enlarge
        The acceleration(g) slope is the differentiation, not the DA. You can clearly see the shifts in the slower pull.
        The slope is close enough that’s it’s mainly the DA
      1. F16HTON's Avatar
        F16HTON -
        Click here to enlarge Originally Posted by Sticky2 Click here to enlarge
        The slope is close enough that’s it’s mainly the DA
        You're probably thinking of the height. I can clearly see multiple gear changes in the acceleration(g) slope in the +2000 DA pull vs the -700 DA pull.

        What you have clearly demonstrated is that "a guy can cherry pick a one run against the other, since you have been fooled". Pay no attention to the man behind the curtain we learned as a child watching the Wizard of OZ.

        Both you and I know that DA affects acceleration, you just happened to pick one of the worst possible examples on the planet to demonstrate it.

        Attachment 58626
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by F16HTON Click here to enlarge
        You're probably thinking of the height. I can clearly see multiple gear changes in the acceleration(g) slope in the +2000 DA pull vs the -700 DA pull.
        I was talking about the height and not the g-force, you're right.

        Click here to enlarge Originally Posted by F16HTON Click here to enlarge
        Both you and I know that DA affects acceleration, you just happened to pick one of the worst possible examples on the planet to demonstrate it.
        Well it's not my comparison but the -700 DA runs produced consistently the quickest 60-130's.

        If you want to attribute the G-force to something else go ahead but you don't know if there is a hiccup in GPS sampling or if the reason the -700 DA car is pulling harder is because the DA is playing the main role in it doing so.

        It's an imperfect comparison but there is no perfect comparison that eliminates all the variables and the more people that learn to factor in DA the better as that is the overall point and not what this one guy hit.

        The NHRA has DA adjustment corrections for a reason.
      1. F16HTON's Avatar
        F16HTON -
        The only thing we need to know is SAE J349 JUN90. I'm not sure why you are giving this guy lip service as he is using an apple to describe the flavor of an orange.
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by F16HTON Click here to enlarge
        The only thing we need to know is SAE J349 JUN90. I'm not sure why you are giving this guy lip service as he is using an apple to describe the flavor of an orange.
        You're right and I'm not a fan of his but I am a fan of pointing out DA is a major performance factor when I can.
      1. F16HTON's Avatar
        F16HTON -
        The keyboard warrior could easily take this guys words and twist them in any direction. It would be a shame if somebody were to say that his run from a dig is much slower because his tuner is unable to manage the power off the hit.
      1. Payam@BMS's Avatar
        Payam@BMS -
        Click here to enlarge Originally Posted by F16HTON Click here to enlarge
        The keyboard warrior could easily take this guys words and twist them in any direction. It would be a shame if somebody were to say that his run from a dig is much slower because his tuner is unable to manage the power off the hit.
        I'm pretty sure we can all agree that his point was clear. DA makes a huge difference... If you think otherwise because it's not in a controlled environment with same everything happening you're delusional.
      1. F16HTON's Avatar
        F16HTON -
        Click here to enlarge Originally Posted by Payam@BMS Click here to enlarge
        I'm pretty sure we can all agree that his point was clear. DA makes a huge difference... If you think otherwise because it's not in a controlled environment with same everything happening you're delusional.
        For sure, that is what makes the draggy such a great tool.
      1. Emre@Esmotor's Avatar
        Emre@Esmotor -
        Click here to enlarge Originally Posted by F16HTON Click here to enlarge
        The keyboard warrior could easily take this guys words and twist them in any direction. It would be a shame if somebody were to say that his run from a dig is much slower because his tuner is unable to manage the power off the hit.
        Unfortunately you do not know how to read a graph.

        at 60mph both graphs have almost 1 G and average is about same till 77.5mph.
        so its not about launch.

        I know what you are trying to do but you are on the wrong point bud.
      1. allmotor_2000's Avatar
        allmotor_2000 -
        What are you saying.. East Coast runs don't count Click here to enlarge