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Thread: VCM Scanner: Log information accuracy

  1. #1
    Tuner in Training
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    Oct 2020
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    Iowa/Florida
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    VCM Scanner: Log information accuracy

    I'm sure most of you have been at this much longer than I have. I have a quick question..

    How accurate are the torque and boost PSI numbers that are logged by VCM Scanner?

    I'm not trying in anyway to replace going to the dyno, however, I'd like to understand the accuracy of the numbers that the VCM Scanner produces for our cars. Mine is a 2011 S4 (B8). I would assume that, at best, it is generating calculated, or ECM produced, numbers for all PIDs, and from torque perspective what is expected at the crank. Is there a correction factor I should be using when looking at the raw numbers?

    Just curious...

  2. #2
    Boost should be an actual reading if the car has a MAP sensor, assuming the PID you are logging is using that sensor.

    Torque is modeled using the airflow entering the engine. Stock I've found this to be pretty accurate but a bit high as it is before any losses to the accessory drive ect. I've found that the farther you stray from stock the less accurate this number becomes. It also depends on how you are changing these models to tune the car.
    Previous
    2007 Mustang GT w/ Whipple supercharger
    2013 Focus ST
    2016 Volkswagen GTI

    Current
    2019 Golf R

  3. #3
    Tuner in Training
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    We are definitely still working through the tuning of this platform. However, I attached a screen shot of my log, this is why I asked.

    Note, CHP (Crank Horsepower) and WHP (Wheel Horsepower) are both being calculated via "Maths" based on Torque and RPM.

    MaxHP_11222020.JPG

    Max Calculated HP

    MaxTQ_11222020.JPG

    Max Torque

    HP_Maths.JPG

    Math used to Calculate HP

  4. #4
    Did you download a scanner layout file from a thread here on the forum? I've never seen any maths pre populated. I've attached a screenshot of a table below. The car is just taking cylinder airmass and RPM and using a lookup table to determine delivered torque. The torque number is only as accurate as the lookup table.

    Capture.PNG
    Previous
    2007 Mustang GT w/ Whipple supercharger
    2013 Focus ST
    2016 Volkswagen GTI

    Current
    2019 Golf R

  5. #5
    Tuner in Training
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    Oct 2020
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    Iowa/Florida
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    Scanner layout was populated via pulling in the individual PIDs, not downloaded. Maths were put in by me based on research on HP Tuners on how to calculate HP (readily available in multiple areas in the overall forum and the internet). That said, are you saying that, even logging a stock S4 with no editing/configuration of any tables or resources, the numbers are relatively inaccurate?

    I do have to notate again, I was "told", when I bought the car, as well as after an inspection, that the car is 100% stock. I have only added an Injen Intake system.

    MaxHP_base.JPG

    Calculated HP

    MaxTQ_base.JPG

    Torque PID based

    Again, no tuning had been done at this point. Only a base logging. This is before I even bought the credits.

    Ultimately, the numbers are a bit irrelevant to me, more interested in the real life impacts and % increases on daily driving. However, I am interested in the accuracy of at least the torque numbers.

  6. #6
    Advanced Tuner
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    In my experience, the best method for tracking power/torque is using virtual dyno. It basically calculates acceleration based on RPM rate of increase and tire size, accounting for wind resistance, and some sort of correction factor applied and smoothed out.

    If you keep variables to a minimum--flat road (ideally same stretch of road), little to no wind, etc.. I have found it to be very consistent. Some cars tend to read a little high or low depending on other factors that are baked in such as aerodynamic drag data etc.

    when tuning, the only torque value I care about is the internal ecu computed one so I know where in the tables i am operating.

  7. #7
    I'll add that by turning up the boost you are changing the airflow used to calculate torque so it isn't going to be the best for A/B comparisons. For example the stock area of the torque model may be more or less accurate then the higher areas of the model you enter by increasing airflow.
    Previous
    2007 Mustang GT w/ Whipple supercharger
    2013 Focus ST
    2016 Volkswagen GTI

    Current
    2019 Golf R

  8. #8
    Tuner in Training
    Join Date
    Oct 2020
    Location
    Iowa/Florida
    Posts
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    Thanks for the feedback guys, I appreciate it.

    Taking the numbers in the logs out of the picture and only basing things on the net increase (%), I'm looking at the following.

    Manufacturer Base numbers:
    333 HP
    325 ft/lbs Torque

    Current Tune (work in progress)
    HP: 30% increase = 432 HP
    Torque: 28% increase = 416 ft/lbs Torque

    I would assume this to be the, relatively, most accurate way of looking at performance increases. Given:

    Sea level is different for everyone
    Tires and tire size may be different for everyone
    Conditions may be different for everyone
    etc..

    I welcome thoughts here as well.

    So, based solely on the percentage increases, my tuner seems to be doing a pretty damn good job, I believe. I looked at the % increase numbers against stock, and they look really good against:

    Unitronic
    APR
    IE
    O38
    etc.

    I'm really excited to see what the final "stage 1" will look like as we progress, before I get in to my Water/Meth kit. Once all is said and done, I'll get her on to a dyno to see what comes from that. However, in the end, she feels really good. We spent some good time getting KR under control, as the S4 seems to be really aggressive in pulling timing. We are on revision 16 of the tune. I've worked with him on other projects too, and very happy with his work every time.