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  1. #1
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    S3 tuning: what's the difference between the diverter valves and the by-pass valve?

    APR makes a high performance diverter valve

    Forge makes a replacement by-pass valve

    The marketing blurb for both 'sort of' suggests they both have the same function/benefits.

    Is that true? What are the differences?

    If you flash the car, should you change them both?
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  3. #2
    liam's Avatar
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    I thought it was like the difference between quattro and 4motion. That is, same thing, different name.
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  4. #3
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    No. Two different valves, AFAIK. The by-pass valve attaches to the turbo body at the rear of the engine; the DV is attached as part of the pipe circuitry at the front of the engine. It's a mystery?!
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    gareth_oau's Avatar
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    Interesting Conundrum tim (and hi from Ozaudi LOL).

    If they are different (or you have both), does that mean you can change both OEMs for APR and Forge?
    2007 RS4
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    Quote Originally Posted by gareth_oau View Post
    If they are different (or you have both), does that mean you can change both OEMs for APR and Forge?
    That's the question(s):
    Are they different?
    Which should you change?
    Should you change both?
    Are Forge/APR the only choices?

    All the discussions I've found hitherto just talk about "replacing the DV/diverter valve" and it wasn't until I received my replacement Forge bypass valve that I notice it is quite different to the APR diverter valve and, in fact, fits in a different place!
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  7. #6
    warren_S3's Avatar
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    I have the Forge one in the picture you have linked above.

    My mate has the APR one on the picture you linked above (albeit it on a Leon Cupra Mk2 240PS).

    Dump Valve (DV)
    Diverter Valve (DV)
    Blow of Valve (BOV)
    By pass valve

    are all flavours of the same thing. Essentially they are all valves used to hold pressure in the system up to a point regulated by the ECU (usually between 11-16psi on standard cars, and anything upto 24psi on remapped cars).

    Where you are right in saying some are located near the turbo, others are located round the front of the engine.

    The reason for this is that VAG group have had multiple revisions on DV's as diaphragms have been splitting and internals have been ceasing. When the DV was located on the Mk4 Golf VAG platforms, the DV was mounted on the TIP (the OE one had a habit of collapsing under high temp/hard usage). Also the turbo was so close to the DV, it was deemed that this was affecting the reliability of the DV.

    Hence tuners started to cold side relocate the DV's with a long converter pipe to the front of the engine (link) to reduce the temps the DV was exposed to. Supposedly this enhanced performance and lifespan of the DV, whilst sharpening throttle response.

    So what did VAG go and do on the Mk5 Golf??? Mount the OE DV right near the turbo . Well f**king done . So again the problems kick off with the DV's overheating / failing and multiple revisions. When they came to making the new S3, TT-R, Leon Cupra Mk2, and Golf Ed30 someone at the VW engine division had the bright idea of putting the DV frontside of the engine . At last!!!

    So hence the earlier cars DV's are located a the back near the turbo, whereas the new cars are mounted at the front by the fuel pump. Both are the same beast.

    The only other component that sits on or near the turbo on earlier cars is the actuator valve (link), and not many 'non serious' petrol heads use these as it is playing with fire in the wrong hands. The are supposed to increase OE boost pressure if you adjust the tension on the actuator spring, but I wouldn't fancy it much. Don't know much about these myself so I bow to someone elses knowledge if they can help out here. (Hopefully Devon Mikey Boy will read this....)
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  8. #7
    liam's Avatar
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    Going back to my old 1.8T Mk4 GTI days is the bypass valve the same as the N75 valve? Maybe try Osqar on the Tex, pretty sure he did that mod. Also try GizmoGTI.

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    Thanks warren, I really appreciate your contribution...now we're getting somewhere, and I hope others chip in....because I'm still confused!

    So you have the same Forge one as me. My understanding is that is this by-pass valve that replaces the OEM one mounted on the valve flange on the compressor cover of the turbo housing at the rear (see instructions, p1). Is that correct? Is that where yours is fitted?

    If so, then it is a different valve than the remotely located DV that you describe above, for which APR supplies a replacement.

    Now, as I understand it, the VAG turbo-charged system is closed; that is, there is neither a BOV or a dump valve to vent excess charged air to the atmosphere; the VAG system keeps it all within the system and, I guess, ultimately expelled as exhaust gas.

    If that's the case, then there seems to be two flavours of these valves in the system. Does that mean both need to be upgraded, or only one? Clearly, Forge suggests the bypass, while APR suggests the DV. Hence my confusion
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  10. #9
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    Lifted from another site (UK MkIV's):

    In control systems terms a N75 is an actuator. It is a solenoid, effectively used to control either the aspect ratio of VNT vanes (newer turbochargers) or a wastegate (older turbos) for the purpose of boost regulation.
    Why ?:
    Under low boost conditions the aspect ratio is reduced i.e. turbo vanes are closed (or the wastegate is closed) to direct more exhaust fluid towards the turbine, hence increasing the turbine's and consequently the driven compressor's angular speed.
    This increases boost into the engine's air intake, provides enhanced combustion, increasing engine speed. Consequently, increased engine speed also results in faster flowing exhaust fluids which further increases the turbine speed. Following this line of thought, this will again yield increased boost.
    This is a feedback path, which if left unregulated results in positive feedback, whereby a continuously increasing boost stream will ultimately destroy the engine and/or damage the turbo.
    Some means of boost regulation is required to prevent turbine runaway. In older turbos a wastegate would be opened to bleed excess exhaust fluid away from the turbine, effectively limiting the turbine speed and regulating boost (strictly speaking in order to be failsafe, the wastegate should normally be partially open, and would begin closing under demand for boost). I believe that VNT turbos will modify the aspect ratio to effectively limit turbine speed.
    Boost regulation:
    The boost is monitored by a MAP sensor which feeds its signal into the boost control unit (within the ECU). By modulating (PWM) the N75 actuator, the ECU can modify the turbo's aspect ratio (i.e. VNT vane angle) or wastegate, so achieving boost regulation.
    Limp Mode:
    In the event of overboost or a significant boost anomaly/deviation (against actual/expected ECU boost data MAP), the ECU may enter a self defence limp mode mechanism to prevent possible engine damage.
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    Quote Originally Posted by liam View Post
    Going back to my old 1.8T Mk4 GTI days is the bypass valve the same as the N75 valve? Maybe try Osqar on the Tex, pretty sure he did that mod. Also try GizmoGTI.

    Struth, Liam...here I am trying to understand 2 valves, and you throw a third one in!!
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  12. #11
    warren_S3's Avatar
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    Quote Originally Posted by Timbo_S3 View Post
    So you have the same Forge one as me. My understanding is that is this by-pass valve that replaces the OEM one mounted on the valve flange on the compressor cover of the turbo housing at the rear (see instructions, p1). Is that correct? Is that where yours is fitted?
    No, our FOrge DV's are mounted at the front of the engine bay, not a the back near the turbo. If you open the bonnet, look to the right hand front side of the engine cover, our DV is there (if you have a TFSi 2.0T S3 like I do).

    You can even get a ring for the Forge DV to allow it to vent to atmosphere I believe.
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  13. #12
    VRStu's Avatar
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    Quite simply on the 2.0TFSI you don't have a valve like the APR one (if you read the APR blurb it does say except 2.0TFSI).

    The 2.0TFSi uses an electronically controlled valve like this -



    Which when fitted to a 200PS BWA or similar 2.0 TFSi is mounted directly to the turbo -



    There were issues with the diaphragms splitting due to heat and hence the change to mounting at the front on the K04 turbo'd cars.
    Stu.

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    OK, I've clarified my confusion. Thanks everyone for the help.

    The situation is as warrencox and VRStu say: the 8P S3 controls boost pressure via a solenoid controlled valve at the front of the engine, RHS (slightly under the engine cover). The only current after-market replacement for this is the Forge FMFSITVR, which is a replacement bypass valve (as opposed to diverter valve, as the terminology sometimes goes).

    The APR R1 diverter valve does not fit the S3; somehow, somewhere I saw this referenced as a replacement and that's what caused the confusion. That'd be the internet's fault!

    An equal source of confusion are Forge's current installation instructions. I was already in some trepidation after being told there's bugger all room back there, but the way the Forge notes read, it sounded like it was definitely there.

    Anyway, I have the Forge replacement, and I'll now work up the courage to see if I can fit it...probably next weekend

    Apparently, an alternative might be the OEM valve from the TTS/facelift S3. I'd like to know if/when anyone tries this and how it effects performance.

    Perhaps someone with access to the Audi parts directory could post the partn number(s) ??
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  15. #14
    Iggu's Avatar
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    Quote Originally Posted by Timbo_S3 View Post

    Apparently, an alternative might be the OEM valve from the TTS/facelift S3. I'd like to know if/when anyone tries this and how it effects performance.

    Perhaps someone with access to the Audi parts directory could post the partn number(s) ??
    Rabbit222 has already done this mate - search around and you'll find the thread. He had problems with his Forge unit and put one of these new Audi DVs on about 3 weeks ago I think.

    EDIT - here's the link Timbo. http://audi-sport.net/vb/showthread....065#post683065
    Last edited by Iggu; 14th March 2009 at 07:55.
    Phantom Black S3, RNS-E with SDS Hack , BOSE, Sunroof, iPod, ITG CAI, Forge DV, Milltek TBE, Revo Stage 2+, Autotech HPFP, Sachs clutch, Lamin-X, BBS Pescaras, H&R springs, H&R ARBs, NGK Iridium Plugs, Vagcom.

  16. #15
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    Absolutely agree that the Forge instructions are confusing for S3/Leon Cupra Ed30 owners.

    I ended up using the 'drawn picture' at the back, and then guessing the rest.

    Basically if you (and this isn't meant to be condescending, this is instruction purely for someone who may never have fitted one before):

    1) Remove the engine cover
    (Disconnect MAF electrical connection point - rear left of engine cover, the hose clips LHS of engine cover - Now hold the rear right hand side of the engine cover in your right hand, the front left hand side of the cover with your left, and apply diagonal pressure lifting the corners until one side lifts - it will be difficult but wont break). Be sure to note if any engine cover rubbers pop off to collect them up and refit to the engine cover - they may also get stuck on the connector points for the engine cover - check these too. They must be refitted to the engine cover and not left on the connection points before refitting engine cover).

    2) Get your torx screwdriver set (is it a T25?? Can't remember - will check)

    3) Undo the stock DV electrical clip (carefully - mine catch snapped and I had to cable tie it - recommend using a flat blade screwdriver in the catch to unclip it - GENTLY!)

    4) Remove the 4 torx screws that hold the black plastic DV unit (Note at this point there will be a black hanger on the engine side - don't forget to reconnect this like I first did!!!)

    5) Remove the DV unit

    6) Get a microfibre cloth and some solvent based degreasing spray and clean the silver cuff section the DV connects onto

    7) Fit your new Forge DV, and finger tighten the 4 screws (remembering to put the black hanger back on nearest the engine.
    Ensure you remember to attach the Forge supplied silver hanger also - put it on one of the two lower sump facing bolts , preferably the one closest to the windscreen bulkhead.

    8) Tighten the bolts in rotation, moving from one torx screw to the next - if you don't and you get the alignment wrong, the black hanger wont sit square and the bolts will feel very tight to do up - risk of threading the torx bolts

    9) Attach the silicone hoses to the DV

    10) You need to splice in the T-Junction hose that Forge have provided which comes off the manifold area. Fit this in and connect the silicone hoses.

    11) Connect any outstanding silicone hoses to their appropriate connection points - ensure they have no kinks, that they don't cross any sharp metal as this could bring the onset of early leaks through wear in the pipes, and they do not fall into the path of the fan or other moving parts (as per the Forge hand drawn diagram)

    12) Replace the engine cover (Remembering to connect the MAF electrical point near the brake fluid reservoir, the hose connectors and reseat all the engine cover rubbers etc...)

    13) Recheck all the bolts are tight (I'd also recheck this after a week or so to make sure nothing has worked loose)

    I will try and take a pic of mine in situ later today to assist with this.

    Also I have learned something today - I though the APR valve was the equivalent of the Forge, so thanks to VRStu for pointing that out.

    PLEASE NOTE: The information in this guide is to my knowledge the right way to fit a Forge FMFSiTDV on an S3 / Leon Cupra or Ed30. The guide worked for me, and whilst it posted as assistance to others it is not an officially recognised guide. I can accept no responsibility if you fail or damage your car by following this guide. (I feel the compulsion to write this a we live in a blame culture! - you never know)
    Last edited by warren_S3; 14th March 2009 at 14:14.
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  17. #16
    VRStu's Avatar
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    The top picture I posted is actually the newer revision of the valve, a picture provided by Arin@APR.
    Stu.

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    Thanks Warren...that's absolutely brilliant -- much clearer than the Forge instructions...

    Have you experienced any problems with the Forge?

    Iggu...I get the sense reading Rabbit's thread that he also installed a BOV. Is that right? I wonder if that might have been a factor in relation to the problems he encountered?
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  19. #18
    warren_S3's Avatar
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    Quote Originally Posted by Timbo_S3 View Post

    Have you experienced any problems with the Forge?
    No mate, service it after one year of ownership (which was a piece of p1$$) only required undoing the screw top on the dump valve, cleaning the internals, wiping some grease on and replacing 3 'O' rings (used wifes tweezers for this). All in all took 10 mins, and the service kits are free for life as long as you own the DV. Use a GREEN spring if you are NOT remapped, or a YELLOW spring if you are! (Have taken pics, will load them later)

    NOTE: My service kit included a new metal 'plunger' (the bit that moves within the DV. The new one was black instead of silver, and felt 'slippier' - don't know if the black coating is anodizing, teflon coating or what. If you have a silver one may be worth calling Forge for a service kit and changing it as the DV seems smoother running now.
    Last edited by warren_S3; 14th March 2009 at 14:16.
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    Crikey, I am learning more and more! Wasn't aware of either the different springs or the service kit, so I guess I'll get onto Forge to obtain same.

    Sounds like the new plunger might resolve the reported issues about sticking. Thanks mate!
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  21. #20
    Iggu's Avatar
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    Quote Originally Posted by warrencox View Post
    No mate, service it after one year of ownership (which was a piece of p1$$) only required undoing the screw top on the dump valve, cleaning the internals, wiping some grease on and replacing 3 'O' rings (used wifes tweezers for this). All in all took 10 mins, and the service kits are free for life as long as you own the DV. Use a GREEN spring if you are NOT remapped, or a YELLOW spring if you are! (Have taken pics, will load them later)

    NOTE: My service kit included a new metal 'plunger' (the bit that moves within the DV. The new one was black instead of silver, and felt 'slippier' - don't know if the black coating is anodizing, teflon coating or what. If you have a silver one may be worth calling Forge for a service kit and changing it as the DV seems smoother running now.
    Warrencox - might be helping my mate fit one of these to his Ed30 at the weekend.
    Any chance of those pics mate ?
    Ta.
    Phantom Black S3, RNS-E with SDS Hack , BOSE, Sunroof, iPod, ITG CAI, Forge DV, Milltek TBE, Revo Stage 2+, Autotech HPFP, Sachs clutch, Lamin-X, BBS Pescaras, H&R springs, H&R ARBs, NGK Iridium Plugs, Vagcom.

  22. #21
    warren_S3's Avatar
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    Quote Originally Posted by Iggu View Post
    Warrencox - might be helping my mate fit one of these to his Ed30 at the weekend.
    Any chance of those pics mate ?
    Ta.
    I'll try and get them posted up today mate.
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