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Thread: External Wastegate Opening Early

  1. #1

    External Wastegate Opening Early

    I was putting metal locking nuts on my turbo studs (they work great btw! a lot better than lock washers or star washers) and took the external wastegate off (it was doing this before I took the wastegate off, just explaining why the vacuum line was off), when I put it all together I forgot to attach the vacuum line. I suspected I might have forgotten, but I took it for a ride and it was opening at 12-13psi like it was supposed to, so I didn't worry about it (might been getting to 15psi at one point which is fine with me). I eventually double checked the line and it was off, so I attached it, and boost stayed about where it was.

    My question is, why is the wastegate opening at 12-13psi without a vacuum line? It should be a 10psi spring. I have it dumped to atmosphere, so I know when it's opening. I can hear the turbo spooling fine at lower RPMs and the BOV will open if I accelerate kind of hard without getting in to boost, so it seems like the wastegate is shutting all the way.

    One other thing, the turbo seems to spool late (and has been this way before, with both internal and external gates). It doesn't seem to start actually building pressure in the engine until about 3000RPM. It's a TB0348 (Grand National), which should be similar to a S60 on the compressor side, and it has a .48 turbine housing on it (the exhaust wheel looks like a fan compared to the scoops of the TD turbo, supposed to be a better design).

    I have a 3" exhaust
    +40s
    Boost Button cal
    12* base timing
    Ported head (shaved .011 I think, and I have an offset cam key)
    52mm TB with 2pc intake TB inlet ported to match (ish, I could go slightly larger honestly, there is still a slight lip, maybe when/if I go to a Holset)
    5-speed
    Walbro 255
    3-bar map
    FMIC
    Ported exhaust manifold (not hugely ported, but ported larger than gasket for reversion, and the #2 runner bump ground out. I was using sanding rolls, so probably not as open as a vendor might have)
    TBI Cam
    PT Lifters
    MBC (ball and spring, not bleeder)

    So two issues that I want to address I guess:

    1. Wastegate opens at 13psi with no vacuum line (I don't hear the wastegate open until then)
    2. Turbo also seems to build boost late (although I can hear it spinning up before it builds boost). It has done this before the external gate too.
    Last edited by turbodaytona87; 04-06-2014 at 06:31 PM.

  2. #2
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    Re: External Wastegate Opening Early

    I had the opposite behavior from the wastegate on the r/t before the line was put on; it hit somewhere north of 30psi as I backed out of it...on a 10lb spring no less.
    “If the people of the nation understood our banking and monetary system, I believe there would be a revolution before tomorrow morning.” -Henry Ford

  3. #3

    Re: External Wastegate Opening Early

    Lucky!

  4. #4
    turbo addict Turbo Mopar Contributor
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    Re: External Wastegate Opening Early

    What exactly do you think boost is supposed to be set to with your MBC?

    Wastegates open early to avoid boost spikes. This is why fancy electronic controllers main advantages are that they can hold the wastegate closed longer and then react quickly enough to avoid a spike, especially ones that have a learning function.

    Wastegates will open if you have enough exhaust backpressure to overcome atmosphere + the spring. Could be coincidence that its opening at the same boost. You are attached to the lower port right?
    Brent GREAT DEPRESSION RACING 1992 Duster 3.0T The Junkyard - MS II, OEM 10:1 -[I] Old - 11.5@125 22psi $90 [U]Stock[/U] 3.0 Junk Motor - 1 bar MAP [/I] 1994 Spirit 3.0T - 11.5@120 20 psi - Daily :eyebrows: Holset He351 -FT600 - 393whp 457ft/lb @18psi 1994 Spirit 3.0T a670 - He341, stock fuel, BEGI. Wife's into kid's project. 1990 Lebaron Coupe 2.2 TI/II non IC, a413 1990 Spirit 3.0 E.S. 41TE -- 1993 Spirit 3.0 E.S. 41TE -- 1994 Duster 3.0 A543 1981 Starlet KP61 Potential driver -- 1981 Starlet KP61 Parts -- 1983 Starlet KP61 Drag 2005 Durango Hemi Limited -- 1998 Dodge 12v 47re. AFC mods, No plate, Mack plug, Boost elbow -- 2011 Dodge 6.7 G56

  5. #5
    Super Moderator Turbo Mopar Staff contraption22's Avatar
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    Re: External Wastegate Opening Early

    As stated, if you have quite a bit of exhaust backpressure, it builds up against the wastegate and forces it open. Some wastegates have two ports. One to keep the gate closed against exhaust backpressure. The other port is to equalize that pressure and let exhaust pressure open the gate. The boost controller would simply control the differential between those pressures.
    Mike Marra
    1986 Plymouth Horizon GLMF "The Contraption" < entertaining sponsorship offers
    Project Log:
    http://www.turbo-mopar.com/forums/showthread.php?69708-The-Contraption-2013-14&highlight=

  6. #6
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    Re: External Wastegate Opening Early

    How is the wastegate set up?

    I wonder if the stocker just doesn't flow well enough to use an external gate, or that there really isn't an "ideal" place for it.

  7. #7
    Super Moderator Turbo Mopar Staff contraption22's Avatar
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    Re: External Wastegate Opening Early

    Sounds to me like you might have a boost leak somewhere. That creates a situation where exhaust backpressure can several times higher than boost pressure.
    Mike Marra
    1986 Plymouth Horizon GLMF "The Contraption" < entertaining sponsorship offers
    Project Log:
    http://www.turbo-mopar.com/forums/showthread.php?69708-The-Contraption-2013-14&highlight=

  8. #8

    Re: External Wastegate Opening Early

    Quote Originally Posted by Ondonti View Post
    What exactly do you think boost is supposed to be set to with your MBC?

    Wastegates open early to avoid boost spikes. This is why fancy electronic controllers main advantages are that they can hold the wastegate closed longer and then react quickly enough to avoid a spike, especially ones that have a learning function.

    Wastegates will open if you have enough exhaust backpressure to overcome atmosphere + the spring. Could be coincidence that its opening at the same boost. You are attached to the lower port right?
    I am attached to the lower port. I figured that with a 10psi spring and no vacuum line, that it would hit more than 13psi (sometimes will get to 15).

    - - - Updated - - -

    Quote Originally Posted by contraption22 View Post
    Sounds to me like you might have a boost leak somewhere. That creates a situation where exhaust backpressure can several times higher than boost pressure.
    I can see where excess exhaust pressure can open a gate early, but I'm not making the connection with a boost leak. The MBC would block any boost from the wastegate until it got close to it's target PSI right?

    - - - Updated - - -

    Quote Originally Posted by Tbird232ci View Post
    How is the wastegate set up?

    I wonder if the stocker just doesn't flow well enough to use an external gate, or that there really isn't an "ideal" place for it.
    I don't know if it's the best way, but the external wastegate is fed from the stock wastegate hole. I have a flange that keeps the waste and main exhaust holes separate. Then the wastegate dumps to atmosphere.

  9. #9
    Super Moderator Turbo Mopar Staff contraption22's Avatar
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    Re: External Wastegate Opening Early

    Quote Originally Posted by turbodaytona87 View Post
    - - - Updated - -
    I can see where excess exhaust pressure can open a gate early, but I'm not making the connection with a boost leak. The MBC would block any boost from the wastegate until it got close to it's target PSI right?
    The turbo uses exhaust energy to spin. When you have a leak on the intake side, it takes much more exhaust energy to reach the boost goal.

    Let's say you have a 1:1 ratio of boost pressure to exhaust backpressure under normal conditions. For every 10 of boost in the intake manifold, you have 10psi of backpressure in the exhaust manifold.

    Now if you have a big leak on the intake manifold side, your turbo has to work harder to make that some 10psi of intake manifold pressure... so the exhaust backpressure has to rise, to 15 or 20psi. That force is pushing against your wastegate valve.
    Mike Marra
    1986 Plymouth Horizon GLMF "The Contraption" < entertaining sponsorship offers
    Project Log:
    http://www.turbo-mopar.com/forums/showthread.php?69708-The-Contraption-2013-14&highlight=

  10. #10

    Re: External Wastegate Opening Early

    Quote Originally Posted by contraption22 View Post
    The turbo uses exhaust energy to spin. When you have a leak on the intake side, it takes much more exhaust energy to reach the boost goal.

    Let's say you have a 1:1 ratio of boost pressure to exhaust backpressure under normal conditions. For every 10 of boost in the intake manifold, you have 10psi of backpressure in the exhaust manifold.

    Now if you have a big leak on the intake manifold side, your turbo has to work harder to make that some 10psi of intake manifold pressure... so the exhaust backpressure has to rise, to 15 or 20psi. That force is pushing against your wastegate valve.
    Interesting...I can do a boost leak test sometime (maybe not til the weekend)

  11. #11
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    Re: External Wastegate Opening Early

    Are you using the stock gn turbine wheel in a different housing? If so that is probably the reason for the slow response. It will fit in the .48 housing but it's mismatched.

  12. #12
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    Re: External Wastegate Opening Early

    I agree that you need to pressure check before diagnosing anymore. BTW, also put a few psi of pressure into the wastegate ports and see if there are any leaks (diaphragm). Also consider taking the wastegate apart if you find no leaks in your system.
    Brent GREAT DEPRESSION RACING 1992 Duster 3.0T The Junkyard - MS II, OEM 10:1 -[I] Old - 11.5@125 22psi $90 [U]Stock[/U] 3.0 Junk Motor - 1 bar MAP [/I] 1994 Spirit 3.0T - 11.5@120 20 psi - Daily :eyebrows: Holset He351 -FT600 - 393whp 457ft/lb @18psi 1994 Spirit 3.0T a670 - He341, stock fuel, BEGI. Wife's into kid's project. 1990 Lebaron Coupe 2.2 TI/II non IC, a413 1990 Spirit 3.0 E.S. 41TE -- 1993 Spirit 3.0 E.S. 41TE -- 1994 Duster 3.0 A543 1981 Starlet KP61 Potential driver -- 1981 Starlet KP61 Parts -- 1983 Starlet KP61 Drag 2005 Durango Hemi Limited -- 1998 Dodge 12v 47re. AFC mods, No plate, Mack plug, Boost elbow -- 2011 Dodge 6.7 G56

  13. #13

    Re: External Wastegate Opening Early

    Quote Originally Posted by wallace View Post
    Are you using the stock gn turbine wheel in a different housing? If so that is probably the reason for the slow response. It will fit in the .48 housing but it's mismatched.
    Supposedly this was a Ford .48 housing that was machined for the GN wheel, I can't confirm that though. I think my friend ran the turbo with the GN housing and the guy my friend got the turbo from is the one who said it was machined. That makes sense however. How is it mismatched? Not questioning your statement, just want to learn more about it.

    - - - Updated - - -

    Quote Originally Posted by Ondonti View Post
    I agree that you need to pressure check before diagnosing anymore. BTW, also put a few psi of pressure into the wastegate ports and see if there are any leaks (diaphragm). Also consider taking the wastegate apart if you find no leaks in your system.
    I thought if the diaphragm was bad, the wastegate wouldn't open at all or at least late. Wouldn't early opening be a weak or broken spring?

  14. #14
    Super Moderator Turbo Mopar Staff contraption22's Avatar
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    Re: External Wastegate Opening Early

    Quote Originally Posted by turbodaytona87 View Post
    Supposedly this was a Ford .48 housing that was machined for the GN wheel, I can't confirm that though. I think my friend ran the turbo with the GN housing and the guy my friend got the turbo from is the one who said it was machined. That makes sense however. How is it mismatched? Not questioning your statement, just want to learn more about it.
    The turbine housing needs to be machined closely to the OD of the turbine wheel. Otherwise exhaust can easily bypass the wheel without forcing it to spin.
    Mike Marra
    1986 Plymouth Horizon GLMF "The Contraption" < entertaining sponsorship offers
    Project Log:
    http://www.turbo-mopar.com/forums/showthread.php?69708-The-Contraption-2013-14&highlight=

  15. #15
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    Re: External Wastegate Opening Early

    [QUOTE=turbodaytona87;1036163]Supposedly this was a Ford .48 housing that was machined for the GN wheel, I can't confirm that though. I think my friend ran the turbo with the GN housing and the guy my friend got the turbo from is the one who said it was machined. That makes sense however. How is it mismatched? Not questioning your statement, just want to learn more about it.

    - - - Updated - - -

    The gn turbine wheel is much shallower than a standard garrett wheel. I was going to use the gn turbine as well but after comparing them I ended up paying for a stage II wheel. I still have the gn wheel I'll snap a picture of the two side by side.

  16. #16
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    Re: External Wastegate Opening Early

    Quote Originally Posted by turbodaytona87 View Post
    Supposedly this was a Ford .48 housing that was machined for the GN wheel, I can't confirm that though. I think my friend ran the turbo with the GN housing and the guy my friend got the turbo from is the one who said it was machined. That makes sense however. How is it mismatched? Not questioning your statement, just want to learn more about it.

    - - - Updated - - -



    I thought if the diaphragm was bad, the wastegate wouldn't open at all or at least late. Wouldn't early opening be a weak or broken spring?
    I would just be thorough. You want to solidly count things as not being your problem so you get closer to what is wrong. I tried looking up wastegate failures and one guy kept having springs fail and his diapragm would get messed up too. Tial said he was buying fakes from the particular vendor he was using. I would say many people with poor wastegate location can suffer heat failures, especially if there is an inherent flaw in their wastegate. Many here seem to get away with wastegate torture.

    Pressure check everything. Even if it doesn't uncover a problem its very important to know you don't have any serious leaks.
    Brent GREAT DEPRESSION RACING 1992 Duster 3.0T The Junkyard - MS II, OEM 10:1 -[I] Old - 11.5@125 22psi $90 [U]Stock[/U] 3.0 Junk Motor - 1 bar MAP [/I] 1994 Spirit 3.0T - 11.5@120 20 psi - Daily :eyebrows: Holset He351 -FT600 - 393whp 457ft/lb @18psi 1994 Spirit 3.0T a670 - He341, stock fuel, BEGI. Wife's into kid's project. 1990 Lebaron Coupe 2.2 TI/II non IC, a413 1990 Spirit 3.0 E.S. 41TE -- 1993 Spirit 3.0 E.S. 41TE -- 1994 Duster 3.0 A543 1981 Starlet KP61 Potential driver -- 1981 Starlet KP61 Parts -- 1983 Starlet KP61 Drag 2005 Durango Hemi Limited -- 1998 Dodge 12v 47re. AFC mods, No plate, Mack plug, Boost elbow -- 2011 Dodge 6.7 G56

  17. #17

    Re: External Wastegate Opening Early

    [QUOTE=wallace;1036250]
    Quote Originally Posted by turbodaytona87 View Post
    Supposedly this was a Ford .48 housing that was machined for the GN wheel, I can't confirm that though. I think my friend ran the turbo with the GN housing and the guy my friend got the turbo from is the one who said it was machined. That makes sense however. How is it mismatched? Not questioning your statement, just want to learn more about it.

    - - - Updated - - -

    The gn turbine wheel is much shallower than a standard garrett wheel. I was going to use the gn turbine as well but after comparing them I ended up paying for a stage II wheel. I still have the gn wheel I'll snap a picture of the two side by side.
    Is the standard wheel you're taking about the TD scoop wheel? Or the newer designed fan wheel?

    - - - Updated - - -

    Quote Originally Posted by Ondonti View Post
    I would just be thorough. You want to solidly count things as not being your problem so you get closer to what is wrong. I tried looking up wastegate failures and one guy kept having springs fail and his diapragm would get messed up too. Tial said he was buying fakes from the particular vendor he was using. I would say many people with poor wastegate location can suffer heat failures, especially if there is an inherent flaw in their wastegate. Many here seem to get away with wastegate torture.

    Pressure check everything. Even if it doesn't uncover a problem its very important to know you don't have any serious leaks.
    Yeah, that's some solid advice. I'll work on testing it this weekend.

  18. #18
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    Re: External Wastegate Opening Early

    The stock wheel is what I was going to compare I have both of them out of the center sections.

  19. #19

    Re: External Wastegate Opening Early

    Quote Originally Posted by wallace View Post
    The stock wheel is what I was going to compare I have both of them out of the center sections.
    This is a ford housing, so the wheel profile is probably close to the shape it needs to be, and I would be willing to bet the housing was actually machined.

  20. #20
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    Re: External Wastegate Opening Early

    Here are the pics. You can see how shallow the GN wheel is. My understanding is the GN wheel is unique. I compared a ford housing and definitely a mismatch.

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