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Thread: Why not use MAF for entire RPM range?

  1. #1
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    Default Why not use MAF for entire RPM range?

    I've tuned for both MAP(with MAF disabled) and MAF(400 RPM up) and the truck runs good either way. In fact I really cant tell any difference between the two.

    So, why not run completely using MAF or MAP? Why mix the 2 or run the MAF from 4000RPM up?

    Could you zero out VE table, set MAF at 0 RPM and run entirely using the MAF?

    Just curious

    230" Dragster - 2000 LS1, 02020003 Speed Density, PRC 2.5 Heads,
    MS3 Cam 237/242 .603/.609, Vic Jr. intake, Holley 1000CFM TB,
    PowerGlide, 5000 stall converter. 8.70@154 MPH

    My Projects Homepage: http://www.horsepowerracing.com

  2. #2
    Lifetime Member swingtan's Avatar
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    Short answer, Yes.

    Long answer....

    There are certain times where the MAF will simply not work correctly, some of these would be...

    • Big cam with high overlap: This causes air flow reverberation at certain RPM's that cause the MAF to read incorrectly.
    • Intake setups that move the MAF: Sometimes, relocating the MAF can cause measurement issues, especially if the MAF is directly in front of the TB.
    • The MAF tables in some OS's have maximum limits of 512gm/S air flow. In FI installations, the actual airflow can exceed this value, meaning you loose fine control of the fueling over this point.
    • The MAF "will" cause an amount of intake restriction. If you are going all out for power, you may decide to remove the MAF because of this. The amount is likely to be very, very small.
    • The MAF can introduce a "computing delay" for the fueling. The further the MAF is away from the TB, the longer it takes for it to read airflow changes. Because the MAP sensor is inside the manifold, it sees changes in pressure much sooner.


    Some of the above are pretty marginal on the effects they would have. For me, I see two general rules for the MAF vs MAFless debate.....

    1. For older ( slower CPU ) controllers like the LS1, MAFless seems to give excellent results when running COS3 or COS5.
    2. For newer ( faster CPU ) controller like the E38, MAF based tunes work extremely well unless you run into the problems above. If the same sort of COS deail was available for the E38, this might change, but for a daily driver ( especially a manual ) a few of us have found that retaining the MAF makes for a more enjoyable driving experience.


    It comes down to what the car is going to be used for. If you were talking about your drag car, I'd probably go MAFless no matter what the controller was. But I'd be trying both and seeing what worked the best at the track.

    Simon.

  3. #3
    R.I.P Shawn, 1956-2011 WeathermanShawn's Avatar
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    Dragster:

    I have tried zeroing out the VE Table. Car (LS1) would not start. IMO it still looks for VE Values to start..both cranking and 'regular' VE.

    You can run total MAF easily (non-idle). Where you might miss the VE Table's influence is on sudden throttle transients. It seems to take the MAF about 1/2 second to react..MAP appears instantaneous. I.E. Dynamic Fueling may be adversely affected. It is subtle, but important.

    It is an interesting question that is not easily answered. And if for no other reason than a legitimate MAF failure, to have no values in the VE Table would be disastrous. So even though the MAF may be primarily controlling Trims, Spark, and steady-state fueling..you have to have a back-up if the MAF fails.

    Good question..
    2002 Black Camaro Z-28 M6 Hardtop 11.0:1CR 425HP/410TQ SAE (400TQ@3500RPM)
    200cc Heads, 228/232 110+2 Cam, 1 3/4" LT's w/catts, GMMG, Koni Shocks, Hotchkis Springs, 35/21 Sways, 17" ZR1's, 3.90 Gears Roadrunner PCM LM-2 Serial Wideband
    EFILive Closed-Loop MAF/SD Hybrid Tune..


  4. #4
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    Great information guys.

    Now, I think I read somewhere that there are certain transmission functions that will only work with the MAF operational like shift times D1108-D1110, is this true and is there more functions that get negated with the omission of the MAF?

    There's a FI setup that incorporates the MAF in the throttle body. Wouldn't this give instant response or at least cut down on the reaction delay?

    Could it be possible to run any size engine, any amount of cylinders and any amount of HP purely on the amount of air flow? If you new the amount of air being delivered you should be able to add fuel accordingly. To me if the MAF sees x amount of air flow it could represent a 4 banger at 50% throttle or a 632CI at 5% throttle and in either case it would inject the same amount of fuel to maintain 14.68 AFR or what ever you choose.

    I'm just thinking out loud as I wonder why FI as it sits right now is fairly complicated with so many tables effecting each other. I've used the Holley commander 950 on several cars and it's so damn simple and easy yet works so well. And now I see so many self tuning setups and I'm wondering how they are doing it....

    Lee

    230" Dragster - 2000 LS1, 02020003 Speed Density, PRC 2.5 Heads,
    MS3 Cam 237/242 .603/.609, Vic Jr. intake, Holley 1000CFM TB,
    PowerGlide, 5000 stall converter. 8.70@154 MPH

    My Projects Homepage: http://www.horsepowerracing.com

  5. #5
    Joe (Moderator) joecar's Avatar
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    GM have made it like this (seemingly complex) so that it fail-safes itself when something goes wrong...

    and it detects unsafe conditons and protects the powertrain...

    and it helps you diagnose problems (DTC's and the various scanner modes).

  6. #6
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    Anyone have info on this:

    "Now, I think I read somewhere that there are certain transmission functions that will only work with the MAF operational like shift times D1108-D1110, is this true and is there more functions that get negated with the omission of the MAF?"

    230" Dragster - 2000 LS1, 02020003 Speed Density, PRC 2.5 Heads,
    MS3 Cam 237/242 .603/.609, Vic Jr. intake, Holley 1000CFM TB,
    PowerGlide, 5000 stall converter. 8.70@154 MPH

    My Projects Homepage: http://www.horsepowerracing.com

  7. #7
    R.I.P Shawn, 1956-2011 WeathermanShawn's Avatar
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    Dragster:

    Not sure on the tranny, but unless you run COS, most OS's will default to a Low-Octane Spark when the MAF is disabled.

    Seems like EVAP is affected also, and I have seen some threads on Dynamic Fueling/Misfire Detection, etc..

    A lot can be overcome with a COS, but it shows how MAF-enabled vehicles seem to be designed..well around the MAF..
    2002 Black Camaro Z-28 M6 Hardtop 11.0:1CR 425HP/410TQ SAE (400TQ@3500RPM)
    200cc Heads, 228/232 110+2 Cam, 1 3/4" LT's w/catts, GMMG, Koni Shocks, Hotchkis Springs, 35/21 Sways, 17" ZR1's, 3.90 Gears Roadrunner PCM LM-2 Serial Wideband
    EFILive Closed-Loop MAF/SD Hybrid Tune..


  8. #8
    Joe (Moderator) joecar's Avatar
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    I have observed effects that seem to indicate the shift times not following the tables while the MAF is failed...

    [ I worded it vaguely because I don't have the data at my finger tips... but yes, I seem to vaguely remember this... my $0.02. ]

    But, yes, various functions seem to disable while MAF is failed.

    To find a way of running SD without failing the MAF would be advantageous.

  9. #9
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    Yes, I'm running CO3 in all my cars!

    It does appear that the factory relies on the MAF, maybe too much.

    Lee

    230" Dragster - 2000 LS1, 02020003 Speed Density, PRC 2.5 Heads,
    MS3 Cam 237/242 .603/.609, Vic Jr. intake, Holley 1000CFM TB,
    PowerGlide, 5000 stall converter. 8.70@154 MPH

    My Projects Homepage: http://www.horsepowerracing.com

  10. #10
    Lifetime Member swingtan's Avatar
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    If I was working at any auto manufacturer, the MAF would be "the sensor of choice". It's a great bit of gear and does so much in a single package. It doesn't measure "air flow" as such, but more along the lines of "intake charge characteristics". The "hot wire" measurement system instantly corrects for both air speed and air density at the same time. The "wire" its self has almost no "thermal inertia" so it reacts very quickly ( it doesn't help that the MAF is normally some distance from the TB though... ). When coupled with a fast ECM, the MAF is a very nice bit of gear and works very well.

    RE: the use of a MAF on any engine. I think you'll find that different engines have differing combustion characteristics and will require differing amounts of fuel. While the same amount of air may be going in, burn rates will vary, optimal spark timing will change and even the RPM the engine is doing will alter the efficiency of the motor. In an ideal world, where all thing are equal, I think you are right. But once you change too many factors, like RPM,cylinder size, combustion chamber shape, valve timing/ lift, etc. then too much has happened.

    Simon.

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