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Thread: Trying to understand base fuel tables

  1. #1
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    Trying to understand base fuel tables

    Ok So as the title suggest I am trying to understand the base fuel table, it seems simple enough at a particular throttle position and RPM a desired lambda is commanded but what I don't understand is why are they set so rich on an N/A falcon as opposed to a turbo?

    If I compare various N/A tunes to various turbo tunes the turbo tunes commanded lambda all appear to be leaner.

    Can anyone please shed some light on this for me? have I missed a part of the equation?

    Thank you in advance to anybody able help educate me.

  2. #2
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    Ok so in part maybe I can answer my own question for the next persons benefit at least. I have revisited the speed density thread

    https://forum.hptuners.com/showthrea...n-Ford-Turbo-6

    From the aforementioned thread (Or rather it's attached files by Darrylc)

    Fuel Mass = AirMass / (Stoich AFR * Desired Lambda)

    There is a separate equation for AirMass which is

    AirMass = (MAP – “MAP at Zero Airmass High Res”) / “MAP per Airmass High Res”

    Yet to my limited understanding it still appears that the base fuel table for the NA falcon is set richer than the Turbo version.

    E.G looking at the table "FUEL BASE vs RPM vs TPS" at 3000rpm and a TPS of 34.2

    Turbo = 0.97 or 14.259 parts of air per one part of fuel
    Naturally Aspirated = 0.89 or 13.083 parts of air per one part of fuel

    Or using a MAP of say 14.65 at the 3000rpm a TPS of 34.2 and a cam angle of 10 deg I ended up finding that the FUEL MASS for the N/A car would be 0.00001628 higher than the turbo.

    Where the hell have I gone wrong with my math???

  3. #3
    Quote Originally Posted by Cracka View Post
    Ok So as the title suggest I am trying to understand the base fuel table, it seems simple enough at a particular throttle position and RPM a desired lambda is commanded but what I don't understand is why are they set so rich on an N/A falcon as opposed to a turbo?

    If I compare various N/A tunes to various turbo tunes the turbo tunes commanded lambda all appear to be leaner.

    Can anyone please shed some light on this for me? have I missed a part of the equation?

    Thank you in advance to anybody able help educate me.
    Is it because the injector high and low slope values and calibrations are different between n/a and turbo, even though it is still the same size injector?

  4. #4
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    which tunes are you looking at? lol
    if you're comparing the base fuel table, theres only a small patch of cells that are different but mostly by only .5 - 1.
    sure it's silly that the na is that lil bit richer, theres lots of shit in the factory tunes that wont make sense if you go looking lol.
    I saw the most differences around 4000-6000 50ish% throttle, you'd be way more likely to be either full throttle or cruising with light throttle in closed loop anyway.

  5. #5
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    Thank you both! I had almost given up any hope of anyone answering my call for education, I've been reading and learning and trying to understand but as I don't have all of my equipment yet I'm yet to really dive in and make changes to see the results.

    JVK I would have thought that the fact that they have calibrated the injectors differently was more to do with the fuel pressure regulator being different with the end goal of course being to deliver more fuel under boost, as for the commanded lambda I would have hoped that they would have made the strategy so that if you were commanding a lambda of 0.96 via these tables that it would actually be aiming for that as part of the FUEL MASS equation. But maybe you are right and that's how Ford have done it

    misk you are correct, heaps of shit doesn't make sense! especially to me, it's early days on my Ford tuning journey and little things like this make it difficult for me to understand the rhyme or reason behind how Ford have setup these strategies.

    The only way for me to ever know for sure what is going on will be to get a wide band and log it, I bet if I do that I'd find the N/A is running rich AF! but that would be no great discovery I think everyone already knew that.

    I've attached two tunes from the repository for reference, these are just one example but it's pretty well every stock tune I've looked at including between my 2003 XR6 Turbo and the Mr's 2004 SX Territory and my mates 2004 BA XR6 N/A. All four speeds too.

    2002 BA 4spd NA.hpt2002 BA XR6 Turbo 4 Speed.hpt