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    Boost, Wastegate DC, Backpressure

    Iím curious about high boost and what peeps look for in wastegate DC. Can the wastegates approach a closed position in the top end? OR is the pressure leaving them partially open even at 100% DC? I would think a fully closed wastegate would be bad due to manifold pressure, reversion, etc.

    Also curious about boost ceiling for stock turbos with stock exhaust versus aftermarket downpipes. Looking at the compressor map, no prob running high boost with stock exhaust due to the small turbos, BUT I take it turbine pressure differential is the main issue. Do you watch EGTs mainly to find this limit? WGDC would also give some indication, but it would be a similar situation if you were reaching choke limit of the compressor.

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    Usually 14-15 psi is considered the safe level with bolt ons and downpipes. Sure you could push 15psi with stock DPs but the back pressurr and EGTs are prolly approaching the danger zone. On every turbo car the wastegate is open at high rpm and high throttle because if it was closed, it would be making too much boost and either trigger an overboost code or on an older car, blow the turbo up lol.

    Stock exhaust I heard is good for 350-400hp at least before it becomes a problem. The biggest restriction is the downpipes, they are quite small, but the secondary cats in the exhaust are 2.25" inlet and outlet...not so bad for a stock turbo car.
    Last edited by Itsbrokeagain; 08-08-2011 at 09:21 PM.

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    matt is right. if you look at the td03-10t compressor map you'll see why. the other site has a great sticky on it here: http://www.e90post.com/forums/showthread.php?t=256804
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    Per the compressor map we can push some fairly high boost... this doesn't really explain the exhaust side. There have been a couple n54's pushed to very near 100% WGDC in the top. My question was related to the exhaust side and pressure in the manifold between the valve and turbine. At 100% is the WG actually closed or the pressure keeping it open? Can all the exhaust gases be expelled past the turbine only at peak HP (most exhaust flow)?

    When only looking at the compressor map you really just move the rpm plot to the right with higher flowing exhaust so the boost ceiling would be similar with our turbos at least. But the pressure difference across the turbine determines the engine efficiency and thus a different boost ceiling.

    Just curious, not going to push it on my car.

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    josh you have to realize (im surprised you haven't seeing what you do know) the turbine on the td-03 is already too small for the compressor. this is why we see a significant torque drop past 5k with the upgraded compwheel/clipped turbine upgrades. the most important piece to upgrade when looking at the turbos is the turbine, but why do it without the compressor? this is why we have companies putting out chra upgrades.

    as for the wastegate question, with stock turbos (stock turbine to be exact) you may see a slight opening at wot because of the amount of back pressure and because of the stock actuator's weakness. im not an engineer so i cannot answer this question very technically, but why are you asking these questions? if you dont mind me asking... this thread and the vanos thread have me wondering what your true motive is.
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    Click here to enlarge Originally Posted by oddjob2021 Click here to enlarge
    josh you have to realize (im surprised you haven't seeing what you do know) the turbine on the td-03 is already too small for the compressor. this is why we see a significant torque drop past 5k with the upgraded compwheel/clipped turbine upgrades. the most important piece to upgrade when looking at the turbos is the turbine, but why do it without the compressor? this is why we have companies putting out chra upgrades.

    as for the wastegate question, with stock turbos (stock turbine to be exact) you may see a slight opening at wot because of the amount of back pressure and because of the stock actuator's weakness. im not an engineer so i cannot answer this question very technically, but why are you asking these questions? if you dont mind me asking... this thread and the vanos thread have me wondering what your true motive is.
    Just curious. Thereís a point when increasing air mass / decreasing VE are counter productiveÖ Iím sure some people maybe at this point and lowering boost would actually equal similar air flow. Itís tough to understand WG position thoughÖ the actual amount open/closed.

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    You should even really worry about that until RB turbos get maxed out. Right now the biggest restriction of all is the turbine housing...on a stock turbo we have explored the limits pretty much 100%...if you are lowering boost and getting similar airflow, that should tell you something, that the user is pushing the turbos beyond the choke point, the point where they simply cant flow anymore and just heat excess air and shorten the life significantly. We are not running huge turbos here where making changes to VE or changing duty cycles or Vanos setting will make a drastic difference in power with less/more boost...we are running pea-shooters that, well out of the box, are already below average, and that is the biggest bottleneck of all.

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    Click here to enlarge Originally Posted by oddjob2021 Click here to enlarge
    matt is right. if you look at the td03-10t compressor map you'll see why. the other site has a great sticky on it here: http://www.e90post.com/forums/showthread.php?t=256804
    Click here to enlarge

    Click here to enlarge

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    Click here to enlarge Originally Posted by Matt@Camber-Toe Click here to enlarge
    You should even really worry about that until RB turbos get maxed out. Right now the biggest restriction of all is the turbine housing...on a stock turbo we have explored the limits pretty much 100%...if you are lowering boost and getting similar airflow, that should tell you something, that the user is pushing the turbos beyond the choke point, the point where they simply cant flow anymore and just heat excess air and shorten the life significantly. We are not running huge turbos here where making changes to VE or changing duty cycles or Vanos setting will make a drastic difference in power with less/more boost...we are running pea-shooters that, well out of the box, are already below average, and that is the biggest bottleneck of all.
    If the turbine is the limitation, can you say the compressor is choking? I would think you've reached the turbine rpm limit. With upgraded turbos we are decreasing the turbine A/R which essentially expands the compressor map to the right.

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    Click here to enlarge Originally Posted by JoshBoody Click here to enlarge
    If the turbine is the limitation, can you say the compressor is choking? I would think you've reached the turbine rpm limit. With upgraded turbos we are decreasing the turbine A/R which essentially expands the compressor map to the right.
    to a point, but there is only so much air you can move through the compressor before it is doing nothing but heating up the air and becoming really inefficient.

    Have you ever held one of these turbos in your hand? You would see what I mean...they are literally like 1" inlet size..

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    I am wondering about the size of the stoch turbos, what garret unit would be similar g22's? Or are they even smaller?
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    there is a great reference picture posted years back on one of the first turbo de-installs done. it has the turbo and mani horizontal on a bench and a standard deck of cards is taller than the compressor housing! the only thing above it is the actuator. let me try to dig that one up.
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    found it, took less time than i thought, google is the ownerer Click here to enlarge http://www.e90post.com/forums/showthread.php?t=78155 look at the OP date/time stamp Click here to enlarge

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  15. #15
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    Hmmm the wife's Santa Fe has a much bigger garret unit then my 335 Click here to enlarge
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    Click here to enlarge Originally Posted by JoshBoody Click here to enlarge
    Iím curious about high boost and what peeps look for in wastegate DC. Can the wastegates approach a closed position in the top end? OR is the pressure leaving them partially open even at 100% DC? I would think a fully closed wastegate would be bad due to manifold pressure, reversion, etc.

    Also curious about boost ceiling for stock turbos with stock exhaust versus aftermarket downpipes. Looking at the compressor map, no prob running high boost with stock exhaust due to the small turbos, BUT I take it turbine pressure differential is the main issue. Do you watch EGTs mainly to find this limit? WGDC would also give some indication, but it would be a similar situation if you were reaching choke limit of the compressor.
    A couple years ago I did some high boost testing and found at around 22psi with the stock compressors (FBO) it was likely the wastegates were blowing open despite the 100% DC. Here's what it looks like on a dyno:

    Click here to enlarge

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