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Another UrS6 Avant build (biggish turbo)

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  • Another UrS6 Avant build (biggish turbo)

    Starting a new thread for the UrS6 Avant I just picked up. I know, I haven't updated my S2 thread at all, but the car hasn't really broken or needed anything, so I have just been driving it as my daily commuter. The UrS6 runs and drives, but needs clutch work as the pedal is broken and the hydraulic system is weak, and the heater core has failed and is leaking inside the car. The car was also involved in a minor front end collision leaving some wounds on the front bumper and headlight assembly that will need to be addressed. Steering rack is leaking some and the boot is torn wide open on the left side, so it will need a refreshed rack installed. I already have enough street time with the C4 platform and don’t have a need for this car as a daily-driver at the moment, so I’m going to tear it apart for a rebuild over the winter months. I figure the steering gear is easier to do when the engine is out, so I'll pull the engine and modify it while I am in there.

    What I'll be doing on this one is a budget build of sorts; shooting for the 550 Bhp range. I was able to get a lot of key parts at very low prices by sitting and waiting patiently for deals to pop-up. I wanted to document an actual build process so I can easily duplicate this setup on several chassis’ I have sitting around, while maintaining a reliability factor and be able to easily bullet-proof this system for track use as well as street use. I know reliability and budget builds don’t typically go hand in hand, but I have done other trials while retaining stock motronic brains and a pegged K24-7200 and so far only the fueling system has been an issue, and that was an easy resolve.

    The kit that I have to work with so far:

    -Spare low mileage (83k) AAN long-block to save on down-time. Minor crack on cylinder 3 head at the spark plug hole. Not concerning at this time.
    -DM Forged H-beam rods
    -Comp-Turbo 54/56 with K26 0.83 A/R housing. Journal bearing, very similar to a K27 #7 (SQ) turbo in size with slightly newer bearing and compressor-wheel technology. The 0.83 A/R housing might be a little slow to spool, but I believe will be manageable.
    -Dahlbeck tuning software on a stock motronic ECU and Vmap sensor, two software versions, both were made for the K27 turbo, and I will have to closely monitor how they do with the Comp Turbo, hoping they will operate without much modification. After studying the turbo maps I was able to source, they look like it should be very close to the same spool and efficiency overall with very comparable flow rates.
    -7A exhaust cam, I've had good luck with just running the exhaust cam and stock AAN intake cam.
    -Stock AAN pistons will be reused, only cleaned and with new rings. Might have these coated. It will honestly depend on timing and local shop abilities.
    -Block was sent out for very light honing. Factory cross-hatching still present with no lip on the upper bore. Should be great to reuse.
    -Full rotating assembly with aluminum flywheel were sent for balancing. The DM Forged rods usually are pretty well balanced end-to-end, but I'm curious to see how they are.
    -Fidenza flywheel, spec up-rated clutch. I have a "Stage 3" unit new in box, but may install a "Stage 5" for reliability with this power level. I might just risk it and see how the Stg3 handles the power.
    -Cylinder head is getting a very minimal treatment with a light port, new cam followers, and I’m thinking about swapping out the exhaust valves to get rid of the sodium filled units. Although, my 32psi K24-7200 car has stock valve-train and hasn’t had an issue, so I may take the gamble and leave the stock valves.
    -New AN lines with the Teflon coating for the oil and coolant lines to the turbo
    -Ebay tubular exhaust manifold with welds gone over and bracing for the turbo
    -Stock Wastegate with a 1.9 bar spring and adjustable cap.
    -Bosch Orange-top injectors rebuilt and flow-matched (as per Dahlbeck’s prior setup)
    -Billet throttle body cam
    -DW300 fuel pump (hoping this is enough flow, jury is still out on this one), otherwise I'll pick up Marc's twin 39mm pump bracket (EFIexpress)
    -Custom front mount single-pass intercooler out of Ray Tomlinson’s old Ursurper build. (this is also where a lot of the other Dahlbeck parts came from)
    -034 Fuel rail with adjustable fuel pressure regulator
    -Stock intake, i may touch up with the dremel some



    In the future if I were to replicate this setup into another car I would not likely be going with the Comp-Turbo brand since they are seemingly more difficult to find and I know more people that can get me a seemingly identical Precision brand turbo for less money with the same specs and also outfit the K26 flange if I need to. The Injectors are in the same position, if I hadn’t gotten a good deal on them I would have gone another route, but they are a reliable setup and don’t require any modification for install, so I will see how they do, plus they I am trying to mimic the exact outfit that was in Ray’s old car since that’s the hand of parts I was dealt. Ideally I would also run stand-alone, but again, the opportunity to run this Dahlbeck setup for the price was an easy decision.

    As far as what custom components will be needed, I have the ability to fab up a down pipe and the custom water and oil lines for the turbo. I will be making a catch can system with custom breather lines and I think I will be running a 7A valve cover with a welded bung on the rear. I’m going to delete as much of the emissions system under the intake as possible, but a stock intake manifold will be used as I don't think my use will exceed what the AAN manifold can flow. Knowing the difference in the inlet flow rates per cylinder on the stock manifold I am planning on running individual EGT sensors to make sure I don't run any cylinders too lean. Anything else I can simplify in the engine bay will be addressed as well. I want to be able to easily service these cars track-side, and the more nonsense I can remove, the better.

    Retaining all amenities means that the air-con is staying, and I have a brand new compressor I shelved a while ago I can use. The A/C equipment appears to be in good shape otherwise.

    OVERALL; Is this the most efficient setup out there? No. Will it be the fastest setup out there? Definitely not. But, for the purpose of a budget build with a reliable journal bearing, and a step up from the K24-7200 I currently have maxxed out, this should be a good starting place. I believe the full cost of this build including the car, shipping of the car, and all of the parts and outsourced labor should be under $8,000. I think in the grand scheme of things, doing the labor yourself, this is the cheapest way to break into the 500hp range on these engines with a reliable, albeit not fully built bottom end. I think 550bhp is going to be asking as much as there is to offer from this turbo arrangement.


    As of right now, the car has been successfully moved inside my storage shop, the engine is out at the machine-shop, and parts are lining up for the rest of the project. More to come, hands will be tied until the machine shop gets back to me.


    PHOTOS TO COME, CAN'T SEEM TO LOAD THEM AT THE MOMENT. I know the forum is having some minor issues lately, will try again tomorrow.

  • #2
    Good luck with the build. Hopefully we can sort the forum soon and you can post some pics
    91 Modded 3B
    14 A6 Avant Black Edition

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    • #3
      Sounds interesting - looking forward to it's progress and pics.
      96 URS6 plus speck saloon
      96 URS6 plus speck estate
      94 2.6 80 Avant
      99 2.8 final edition Cabriolet

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      • #4
        Sounds good, definitely following. If all goes well, I’ll be building mine this winter as well

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        • #5
          Photos attached of the engine tear-down process and the size comparison between a stock K24-7000, a K27 #7, and the Comp Turbo 54/56 being used for this build. The Dahlbeck software was setup for a turbo nearly the same spec as the K27 shown, and the CompTurbo is very close in every way except the K26 vs T3 Hotside flange.
          Last edited by pwbmotorsport; 10th October 2019, 17:08.

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          • #6

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            • #7
              Last three for now. Will update as more work is done.

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