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Thread: What happens when you go into boost?

  1. #1
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    Default What happens when you go into boost?

    I know you go real fast :wink: But really, if you have some type of forced induction, what does the computer use for a spark table at that stage? The spark table stops at 105kPa and I don't see any other provisions such as spark v. rpm at WOT as in the PE table. So does the computer send the same timing number that it was using for 105kPa at a given RPM for anything above 105kPa? Or do you have to revert to other methods to scale everything down? In other words: How the h*** do you tune for force induction without that two bar map support

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    2 bar map support does not affect the spark table in any operating system.

    Spark is calculated from dynamic airflow not map values

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    Quote Originally Posted by Delco
    2 bar map support does not affect the spark table in any operating system.

    Spark is calculated from dynamic airflow not map values
    Woops, your right, got my y axis confused. :oops: Thanks. But let's say that you do not run a maf and run speed density. The VE table stops at 105kpa. Where would the computer get its values at that point. On the other hand, if you did run a maf and it maxes under boost, where do the values come from?

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    Quote Originally Posted by hpcubed
    Quote Originally Posted by Delco
    2 bar map support does not affect the spark table in any operating system.

    Spark is calculated from dynamic airflow not map values
    Woops, your right, got my y axis confused. :oops: Thanks. But let's say that you do not run a maf and run speed density. The VE table stops at 105kpa. Where would the computer get its values at that point. On the other hand, if you did run a maf and it maxes under boost, where do the values come from?
    Thats where a proffesional tuner comes in that recalibrates and modifies the system to run a 2 bar map sensor.

    The ametuer can do it as well - just be prepared to have the possibility of wearing out or breaking the first few engines getting a base tune setup.
    You would experience the same problem if you started from scratch with the stock GM code and didnt have any values in all the tables , that sort of data takes months to years to get right on a dyno.

    As a experiment , go into flashscan and zero all the spark tables , zero the maf and IFR tables as well as the VE table. At this point you still have a big advantage in you know roughly what shape and order of magnitude all those tables should be. Now start tuning the stock vehicle without doing any copy and pasting from from another calibration.
    Thats sort of what its like but you are only doing 4 tables - now go and do all the other 2000+ engine calibration variables and bring them into line - not a easy or quick job.

    The first part of the experiment is exactly what happens when you purchase a code modified calibration ( from any company ) to run 2 or 3 bar.

    If you are going to keep the maf then things become a lot easier as 98% of the work is already done for you as the MAf does not look at VE

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    I think, when a MAF maxes out, the PCM goes to a dynamic airflow calculation based on the maxed MAF values and the VE table.... ?

    The open loop PE vs RPM table can also be used to add more fuel when the MAF maxes out.
    2003 Silverado SS
    N/A: 14.257 @ 94.63 mph
    N2O: 13.200 @ 102.3 mph

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    Quote Originally Posted by deezel
    I think, when a MAF maxes out, the PCM goes to a dynamic airflow calculation based on the maxed MAF values and the VE table.... ?

    The open loop PE vs RPM table can also be used to add more fuel when the MAF maxes out.
    Yes I do not see the fueling as a problem. I just don't see how to compensate for the spark if the maf maxes out.

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    Seems to me if you replace the stock MAP sensor with a 2 bar sensor you essentially need to take all of the tables that refer to MAP and delete every other row and copy the last row into the now empty half of the table. That should make it close to working with the new sensor. I know that's not quite exactly correct, but it ought to be a reasonable place to start. I'd surely do that test before the blower was installed as small mistakes at that point are much less damaging.

    Or am I missing something really big?

    Ira

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    If you put a 2bar sensor on, the PCM will assume at key on (100kPa) that it is in fact about 35 - 40 kPa. The easiest thing to do is adjust the MAP scaler {C6301} to make the value 50kPa at key on (Off the top of my head the number is about 130, up from 94 for a 1bar).
    Then you just have to think in your head to double the actual MAP values.
    So you would see 70kPa in the scan tool, but in reality it would be 140kPa.
    You cannot adjust the scaler so the 2bar reads 100kPa because as soon as you go into boost the PCM has hardcoded limiters to 105kPa.

    You also need to disable the Barometric updates {B0301} or the PCM will adjust the fueling thinking atmosphere is 50kPa!!.

    NOTE: This works on MAF Less setups, not sure about a MAF car.

    Cheers,
    Ross

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    Excellent information - thanks . I have a thought, when the maf maxes out, maybe the computer reverts to engine protection mode? There is a spark vs rpm table for engine protection mode.

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    Quote Originally Posted by GMPX
    If you put a 2bar sensor on, the PCM will assume at key on (100kPa) that it is in fact about 35 - 40 kPa. The easiest thing to do is adjust the MAP scaler {C6301} to make the value 50kPa at key on (Off the top of my head the number is about 130, up from 94 for a 1bar).
    Then you just have to think in your head to double the actual MAP values.
    So you would see 70kPa in the scan tool, but in reality it would be 140kPa.
    You cannot adjust the scaler so the 2bar reads 100kPa because as soon as you go into boost the PCM has hardcoded limiters to 105kPa.

    You also need to disable the Barometric updates {B0301} or the PCM will adjust the fueling thinking atmosphere is 50kPa!!.

    NOTE: This works on MAF Less setups, not sure about a MAF car.



    Cheers,
    Ross
    Ross - Are these the only things that we have to change - every table with map as an axis, map scalar - anything else?

    I think it is a good idea as suggested by Ira to tune the car with the two bar map sensor before adding the turbos. I think I will install the 60 lb injectors as well, get everything running right NA and then add the turbos and finish the tuning.

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