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Hybrid turbocharger k04 build

Discussion in 'A3/S3 Forum (8L Chassis)' started by beachbuggy, Nov 25, 2011.

  1. vtraudt
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    vtraudt New Member

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    Regarding wastegate actuator, spring rate, force:

    Cut up a bad K03 actuator to get some idea of the spring and dimensions:

    Canister (actuator) OD: 59mm
    Spring diameter: 37mm
    Wire diameter: 2.5mm
    Windings: 3 (plus top and bottom)

    Spring uncompressed: 66 mm
    Spring compressed with 11 lbs load: 46mm
    Spring rate: 11 lbs / 20 mm = 0.55 lbs/mm = 14 lbs/inch = 0.25 kg/mm = 2.5 N/mm

    Dimensions: see photos

    https://www.dropbox.com/sh/2ifx7vdb9qr95gu/vc4IhBLaXY

    Also, used a K03 (from 2.7T) for the following 'spring rate' calc:

    Travel: ca. 15mm
    Start pressure: 7 psi
    End pressure: 14 psi

    Based on above: around 2mm per psi.
    With the 'active' diameter the air/vacuum is working on of about 2" or around 3 square inches
    14 psi = 42 lbs
    7 psi = 21 lbs
    spring travel: for 21 lbs = 14mm. Spring rate based on that: 1.5 lbs/mm or 0.675 kg/mm or 6.75 N/mm or 38 lb/in.
    Obviously, a big discrepancy to the above spring rate of 14 lb/inch (not sure what the US unit for spring rate is).

    Flapper active diameter: ca. 25mm or 1 inch. Area: 0.75 square inch

    Backpressure in exhaust manifold to equal spring pressure: Example with 5 psi crack pressure of wastegate:

    5 psi x 3 square inches = 15 lbs preload on the actuator spring.

    15 lbs / 0.75 square inches = 20 psi back pressure required to lift the flapper.
  2. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    all nice calcs but not that relevant to your boost duty cycle control...
    It would not be unusual to see an exhaust manifold pressure far higher than you imagine, depending on setup... Upwards of 2:1 pressure ratio minimum on k03/4 framed turbos...
  3. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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  4. vtraudt
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    vtraudt New Member

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    I thought I need stiffer wastegate spring?

    "2:1 pressure ratio": what is 2 and what is 1? Cylinder pressure 2, exhaust pressure 1?
    In absolute numbers (examples) available?
  5. vtraudt
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    vtraudt New Member

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    "if I go over 21 psi below 4250 rpm the thing will surge": How does 'surge' materialize (in data, and real world)? I don't seem to have the limit, running happily at 25 psi (RS6/2283) (needed to get the desired 21 psi at redline due to "overshoot", but NOT liked since I am on stock rods (and 25 psi at mid range might put too much stress on the stock rods).

    Setup: AMB engine, high flow log manifold, 3" DP, custom TIP, S4 MAF, 550cc. RS6/2283 combo, stock WG spring.
  6. vtraudt
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    vtraudt New Member

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    Any suspicion yet for the boost dropping from 5500 on? N75 with MBC in parallel, stiffer actuator spring, correct?
    Since I have similar issue (overboost mid range or falling boost, depending on perspective), a strong springed actuator was suggested here. IIRC, you put a stronger (borrowed from T3, right) spring already in, but still seeing the 'hump' shaped boost curve.

    There got to be a way to get a flat 22 psi, or?

    What type of MBC are you using? My current trials have been with 'fancy' ball-and-spring MBC (from integrated engineering). On other cars (AEB), I am running the simple 'faucet type' (nothing but an adjustable valve) type MBC. Maybe I need to give the cheapo MBC a chance (only one trial, deemed too touchy and abandoned after a few failed trials to dial it in).

    Note: I also experimented with 'flow modified' N75 (varying the restrictor diameter in the leg to the compressor), hoping reducing the restriction (larger hole = more air flow) would 'speed up' the reaction time of the N75 to 'catch' the boost swing (see earlier N75 only logs), but both trial holes 'overdid' it (the first (2.1mm) resulted in max boost of 15 psi due to too much air getting to the actuator).

    Wish I knew how to manipulate the N75 control...(or tuning the Me7.x for that matter). Certainly on my bucket list for the future...
  7. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    inlet manifold to exhaust manifold... lots more in exhaust manifold than inlet with minimum that sort of pressure ratio on k0x framed turbos
  8. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    Proper N75 control will achieve this. me7 capable of doing it

    if you dont have access to getting this mapped properly, find yourself an EBC which will...
  9. vtraudt
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    vtraudt New Member

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    Will check with tuner. But what EBC 'comes to mind' for this purpose?
  10. vtraudt
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    vtraudt New Member

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    What pressure are we talking about?
    Say 3" DP, not cats, cat back exhaust after the turbo,
    Say high flow log manifold from cyl to turbo.
  11. m19lte
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    m19lte Member

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    Bit of a Resurrection here but wowww what a great write up !
    I have a spare k04 and thinking of having a bash at hybridizing it :)
    I'm quite clear on all of the build other than where abouts was the exhaust/turbine housing machined ? With the proposed Chanel's to help prevent surge ? Thanks great thread
  12. wild willy
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    wild willy Member

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    Is the 0.5mm clearance the total diameter increase in the housing or the distance from each blade to the wall ie diameter increased by 1mm oversized overall.
  13. vtraudt
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    vtraudt New Member

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    Numbers for backpressure floating around out there are up to 60 psi on K04. Realistic? What is stock backpressure (K03, stock manifold, cat)?

    Can high back pressure cause valve lift?

    With respect to valves: is the stock valvetrain of the 1.8T good for 350-400 cHP (7200 or less rpm)?
  14. slappy_dunbar
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    slappy_dunbar Let's Do This

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    60 psi of backpressure in front of the turbine is about the most stock valve springs can tolerate.


    Yes, and the symptoms of it are mis-firing and spiking boost pressures.



    Yes. A small-frame turbo such as a hybrid K04 puts added loads on the cylinder head, but we've seen intake airflows exceeding 280g/s without back-pressure issues.
  15. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    yes. high backpressure can keep "weaker" exhaust valve springs to hold them open... eg high milers for example, agu heads with 100k miles + on them.. It is also an "unknown" in terms of you cannot predict which are weaker or not until they show some evidence of it.. (eg: accepting high levels of ign timing without any torque increase benefit or reduction in egts, and also higher than normal egts where the combustion process is leaking directly into the manifold, causing potentially excessive egts.)
  16. vtraudt
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    vtraudt New Member

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    ==> what is a high mileage stock K03 with cat running (for comparison). I have plug in the manifold: what gauge is used to measure the pressure?



    ==> boost spikes: i try to wrap my head around why valve lift would cause spikes: extra exhaust gas from valve lift spool turbine, pumping more air, higher boost, wastegate (N75 or MBC) not quick enough to catch. Should be a high frequency spike (unlike a boost swing (with quite low frequency).


    ==> not entirely clear why a low restriction (K04 with manifold, DP, cat back) system is causing MORE back pressure than a highly restrictive (tiny manifold, tiny turbine, plugged up cat, low flow exhaust). Can someone explain?
  17. vtraudt
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    vtraudt New Member

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    badger: thanks for the insight. Very interesting. Is boost a factor? RPM (since even healthy new stock springs will float at some RPM (even without combustion, just mechanics from a 'swinger system')? Valve float occurring at higher RPM?

    When measuring (who has logs?) back pressure, what are the driving variables? Should be correlation with g/s (more air in, more exhaust out), AFR (leaner, more exhaust volume), timing pull, EGT (hotter, more volume), turbo turbine (larger, more flow, less back pressure), clipping of turbine, partially open wastegate flapper.

    Has someone run 320 g/sec (with water/meth, high flow intake/heads, high flow manifold, K04 frame turbo, DP not cat, cat back) on stock valves/springs?

    For 280 g/sec: fresh stock springs? (not sure cost vs. upgraded springs)? Or just (cheap enough) get upgraded (how to select? who are the usual suspects and sources) springs when building 280 g/sec or above system (i.e. 2283 project).

    Of the 2283 users out here: who floats? who does not? who is on stock springs? who is on upgraded springs?
  18. slappy_dunbar
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    slappy_dunbar Let's Do This

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    All are contributing factors.

    I don't think I've heard of any 2283-based hybrid turbos which cause valve float in their setups. It's really not that common of a concern on K04-framed turbos. Especially in light of the fact that such turbos are flowing more in the 260s. I don't think I've seen one push into the 280s, actually. For reference, here's its efficiency map:

    [​IMG]
  19. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    292g/s here doug on 2283 wheel'd bbt
  20. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    Not everyone knows or realises vag also did something different on their k04 valvetrain cars..
    There would have been a reason for this.. and backpressures isthe key part here.
    Shimmed their stock springs +1mm

    You can buy cat gold or supertech springs as uprated parts if pushing the small k04 framed hybrids to their full potential. It can only be a good thing.

    I would'nt call it float but being held open from closing.
  21. vtraudt
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    vtraudt New Member

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    270 g/s here, on N75 at about 22 psi (stock MAP sensor limit) steady.
    Try to get a bit more (280) but not sure if it can be done using N75 and stock MAP. Would like to keep the N75 control.
    BTW: has anybody written maps yet for the available higher pressure MAP sensors for the 1.8T?
  22. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    The MAP sensor limit is hard coded in the logic of the map and would require decompiling then replacing in numerous places to allow the use of larger sensors...

    For the most part its irrelevant these days as mapping knowledge has advanced enough that the 1.5bar MAP sensor limit is not an issue in context of using it to manage boost... open loop control will sort that out

    <tuffty/>

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