Boost Readout Discrepancy

Discussion in 'Forced Induction - 5.0L V8 Engine' started by AZtrophy, Nov 1, 2019.

  1. AZtrophy

    AZtrophy Member

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    Anyone notice a significant delta in the boost readout from the dash versus either gauge or ebc? I'm not expecting the 2 to be dead nuts, but they are quite a ways off. See below...

    For reference, I'm running a StageII Procharger kit pulleyed @ ~15psi. Since I'm running pump (91), I added a GFB G-Force III electronic boost controller and a Tial MVR wastegate w/5.8psi spring.

    The dash reads somewhere north of 8psi (I believe I saw 8.9psi at peak) while the GFB peaks between 3.5psi - 3.9psi. As a result, I haven't pumped the duty cycle too much (10%-30%) thus far as I'd like to definitively eliminate the possibility of overboosting if the ebc is incorrect.

    Vacuum seems to be much closer between the two but I can't get as granular there since the GFB only reads whole numbers (inHg).

    Based on the spring pressure, I'm more inclined to believe the dash readout at this point.

    Thoughts?
     
  2. Roush05

    Roush05 Well-Known Member

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    Pretty sure the dash is a calculated value but I forget what it is based off of. Is the gfb tapped into vacuum? Or is it sensor based
     
  3. OP
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    AZtrophy

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    #3 AZtrophy, Nov 1, 2019
    Last edited: Nov 3, 2019
    There's a 1/8 line directly off of the controller which taps into a manifold vacuum source. The 3-port solenoid is connected per GFB's instruction for external wastegates (see pic below).

    Forgot to add, the boost source comes via hose barb tapped into the "hot pipe", just above the WG which is located right before the IC.
    Screenshot_20191101-161216~2.png
     
  4. ugstang17

    ugstang17 Well-Known Member

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    My research on the topic revealed the same as stated in reply #2. Further I found out that 17GT's will not display boost on the LCD display like 15 and 16 GT models. The vac/boost gauge I have in the car however is pretty close to what is displayed on the LCD at idle. So for vacuum purposes it seems pretty reliable. Just install a vac/boost gauge (mechanical) and be done with it. Simple install. If you look in the interior parts or section for electronics/audio/gauges you will see that there is a guy on here that makes a vent gauge mount and it is much nicer and cheaper than the one available on Lethal Performances website. It actually angles the gauge so you can see it without protruding out of the vent. Or you can pillar mount it with the Autometer pillar mount which I hear works out nicely as well.
     
  5. Meatball

    Meatball Well-Known Member

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    So especially on a 2017 the boost estimate via obd2 can be very wrong? (Worse than just inaccurate). I was hoping not to have to install a mech boost gauge in addition to an nGauge / Interceptor
     
  6. ugstang17

    ugstang17 Well-Known Member

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    On the 2017 GT only vacuum is available from my research with regard to LCD display. If the data is there to be used by a third party device such as the Interceptor I cannot answer. I only looked into whether or not the LCD display could be programmed to read vac/boost (since it only shows vacuum) like the 15-16 models have and if so how reliable it is. However I was assured that a mechanical gauge or using the vac/boost sensor required for use with the Ngauge will read more accurate. As for Lund Ngauge you have to purchase a vac/boost sensor to use with Ngauge to collect that data according to Lund AND my local speedshop (Team Beefcake Racing/Finishline Performance).

    This has nothing to do with doing an ecoboost PP gauge swap like many will do. I never looked into that nor had any interest. I prefer aftermarket gauges when it comes to seeking reliable data like boost or fuel pressure etc.
     
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  7. Plimmer

    Plimmer Well-Known Member

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    2015 to 2017 does not have a map sensor. Boost on dash is calculated
     
  8. ugstang17

    ugstang17 Well-Known Member

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    Once again...2017 GT will nor display boost...only vacuum. Only 15 - 16 models had the ability to display even the calculated vac/boost. Verified through VMP and Lund and PBD.
     
  9. Plimmer

    Plimmer Well-Known Member

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    Ok, I have a 2015. Didn’t know the 2017 won’t calculate boost.
     
  10. OP
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    AZtrophy

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    Thanks for the great discussion so far everyone. I thought about adding a mechanical gauge but there are some potential cons as well:
    1. The obvious... buying and installing yet another component. Not the end of the world but it's already getting a bit cluttered.
    2. If the ebc isn't reading properly, I will still have a much higher probability of over-boosting since it's likely reading low.
    3. If the mechanical gauge brings yet another boost reading to the party, I would have 3 possibilities to choose from which puts me further from the goal.
    If I inadvertantly swapped the hoses between ports 1 & 2 on the solenoid, would that have a similar behavior? I don't think that this is the case and I assume that the solenoid is just looking for a delta in pressures. That said, I'd rather not take the bumper off for the 3,000th time unless someone thinks the idea has merit.

    Any other ideas? Thanks again.
     
  11. 96gt4.6

    96gt4.6 Well-Known Member

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    My '17 GT/Whipple'd setup seems to calculate properly. This is with the Whipple stage 1 kit, which states 9psi. My gauge seems to read about right on.

    All I had to do is enable it with ForScan in the cluster As-Built.

    '17 GT Premium, all stock less the supplied Whipple tune/kit.

     
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  12. OP
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    AZtrophy

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    Thanks 96gt4.6, for the confirmation on the readout.

    Guess I'll be pulling the bumper to check everything one. more. time. :headbang:

    Let me know if you happen to have suggestions of what else to check. Current plan is as follows:
    1. Verify no kinks or tears in hoses and that all are still connected.
      • I'm not expecting to find anything since the vacuum seems to read fine.
    2. Verify hose connectivity (ie. is the correct line going to the correct port of the solenoid)
    3. ???
    Full disclosure: I'm not pulling to red line or anywhere close. Shutting it down around 5500 RPM which I suspect should be more than enough to see higher numbers than I am given the pulley + headers + MAK pipe should be good for about 16psi. Couple this with 75% duty cycle on the EBC in the latest pulls and I can't justify seeing less than WG spring pressure, again 5.8psi spring. The peak boost per the EBC on these pulls was 4.9psi.
     
  13. 96gt4.6

    96gt4.6 Well-Known Member

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    No problem. It should be noted, that as others have stated the MAP/Boost is calculated.....not actual. Therefore, this value is determined entirely by the 'boost' value inferred by the tune/engine data. It appears Whipple tunes like OEM, so the calculated 'boost' value is accurate in my instance. However, I have had some say that using this method shows boost levels that are not the actual measured boost level in the manifold, and in some instances far from it.

    Being as my power adder is fixed boost wise, I have no desire to have a different method of displaying the current boost level. However, if I had anything but a PD blower setup, I would certainly have a manual boost gauge installed. Nothing wrong with 'inferred' like this shows, but in instances where the boost can change like a centri or turbo application, no sub for hard measurements in my opinion.
     
  14. Torinate

    Torinate Well-Known Member

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    I agree. I would be looking more for the consistency of the number. Does anyone know if the inferred method is consistent in what it displays? The overall number and its accuracy is not as important as the consistency of the measurement. Make sense? Does the Forscan boost / vacuum gauge display accurately day to day or does it vary outside the norm of temp and pressure changes?
     
  15. OP
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    AZtrophy

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    I would love to be able to trust the values reported on dash but regardless of whether or not that's possible, I need to be able to rely on the reading from the electronic boost controller. I pulled the bumper again and verified everything mentioned above. It all seems to be per the instructions so I'm lost as to why it's reading so low.

    Here's the G-Force3 boost solenoid routing instructions again for convenience.


    Here's my actual setup. As I tried to note, the purple hoses are connected to port 1 and tee; one side to bottom port of WG and the other side to the boost source which is where I tapped my hot pipe. Yellow hose connects to port 2 as well as the top port of WG.
    Boost_Solenoid_Routing.jpg

    Any clues as to what the :curse: is going on here? Thanks again everyone.
     
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