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Thread: Sam's build thread

  1. #1771
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    Very happy boy. I finally got around to finishing the re-shimming of the rear beam. I did string lining before and after and now have an exact (across a 15in rim) 2mm of toe out on each rear giving 4mm total rear toe out. I also added some more neg camber at the same time and look to have - 2.2 degrees. Also swapped out my standard worn rear discs for some meatier yet used DBA T2's. Very stoked because if I'd stuffed up I wouldn't have had time to get another set of shims and fit them up prior to Bathurst in early March and re shimming can be a tad stab in the dark as far as accuracy goes when you are re shimming a car that was previously shimmed, so to land on the exact figures I wanted was great.
    Absolutely loving the string lining too. I have two (front and back) aluminium bars drilled exactly for the string spacing. I just use fishing clips to hang swivelled sinkers off the lines to provide tension on the 80lb yellow braided fishing line which is dead easy to read off against a steel rule. All that is needed is to unroll the lines, place them on jack stands marked for hub centre height, and because the strings are a set width I know the measurements to stand the strings off each sides hubs and can get it all squared up start to finish in 30 mins. Once I'm very close I elastic band the alu bars against the stands and then get it down to as accurate as I can before I start measuring the alignment. The actual measuring of the alignment once its all positioned only takes 30 seconds per wheel.
    Surprisingly the car felt a bit more predictable in the wet through a few test corners than previously. Seemed to want to steer/rail its ar$e around the corner rather than be inclined to slide. It is very responsive on turn on too. Nothing can really be gleaned at street speeds though but so far feels good and its sweet knowing that it is definitively aligned properly at the rear rather than getting some paid for bodgy numbers from an aligner that you just cant trust. Next thing is to check that with the extra tuck that the extra camber has afforded, whether 215/50/15's will now fit. If not I'll have to stay with 205/50/15 medium rears on the circuit and 195/55/15 softs for the hill climbs. Still not certain but I'm pretty sure that although narrower and very second hand and chewed up, that my softs work better than the 10mm wider mediums at the rear in hillclimbs.

    In other news here is a great vid with Mr Mountune talking about Rallycross engine tech. Its interesting that if they run single throttle body, they are making use of dual plenum inlet mani's similar to the VWR Volkswagen Racing and Dahlback style ones used early days on 1.8T 20V's. They run the camera past one at the start of the vid.
    Sam's build thread-oip-jpg

    https://www.youtube.com/watch?v=QdM6oZK1Gd4

  2. #1772
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    Rallycross regs are complex and as a result there are specific engine specifications engineered to suite those regulations. As a result you see "unusual" hardware that is designed to specifically overcome some limitations imposed by the regs. From memory the VW's ran in the category that mandated restrictors of a predetermined size. One of the engineering solutions to help with overcoming the limitations of a restrictor is to make the inlet plenum as large as possible, kind of like a boost storage tank. This helps with maintaining boost while playing with the throttle opening to control the traction. It also delays the response on rapid throttle opening a little to avoid the car breaking into uncontrollable wheelspin. All rather specific rallycross requirements that are not exactly desirable in circuit race cars.

    That's why circuit/track cars have the throttle bodies as close as possible to the inlet valves, as we want instantaneous throttle response. Hence the need for multiple throttle bodies.


    Cheers
    Gary
    Last edited by Sydneykid; 10-02-2020 at 12:15 PM.
    Golf Mk7.5 R, Volvo S60 Polestar, Skyline R32GTST

  3. #1773
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    Ah ok. I'd read that one of the advantages of the dual plenum intakes was that you could run a single throttle plate yet get very even flow distribution to each of the cylinders. But I'd seen flow bench tests done on the Dahlback where despite the EVEN flow distribution to each cylinder, the TOTAL flow was quite restricted compared to a traditional side feed single throttle body plenum I guess because the actual runners are fed through slits in the main plenum.
    Like you say perhaps they have a place on air restricted engines where they can perform a certain function below the threshold where the air restrictor exposes its total flow shortcomings too? An interesting rule though where you can have single throttle plate DBW or cable throttle ITB's but not both. That would have to be a balance of performance rule you'd think. Yeah I guess you have to be careful looking at a race engine and lifting ideas from it without knowing what rules they are trying to engineer their way around.
    Last edited by sambb; 10-02-2020 at 12:48 PM.

  4. #1774
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    I don't know the restrictor sizes for rallycross but they most likely would in the range 32 mm to 36 mm, which is similar to rally cars. Which means 270 bhp to around 380 bhp maximum. That's why maximising WOT airflow isn't an issue, what is their main concern is is transient power after there have been throttle position changes. Hence the large" storage" plenum.

    You could increase the max airflow limit by increasing the width of the slot, tricky to get too with a die grinder though.

    Cheers
    Gary
    Golf Mk7.5 R, Volvo S60 Polestar, Skyline R32GTST

  5. #1775
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    any IPRA test days/rounds coming up Gary where second hand tyres might be up for grabs?

  6. #1776
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    Quote Originally Posted by sambb View Post
    any IPRA test days/rounds coming up Gary where second hand tyres might be up for grabs?
    Round 1 of the 2020 NSW State Championship is on at Wakefield Park 29/2 and 1/3, I'll ask Billy to quarantine any suitable 15"tyres for you.

    Cheers
    Gary
    Golf Mk7.5 R, Volvo S60 Polestar, Skyline R32GTST

  7. #1777
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    that'd be unreal. let us know when IPRA comes to SMSP. A friend of a friend may be running a Clio 182 that he's just put together and I'll be curious if the little mk2 escort turns up that had its engine built by an engine shop near me.

  8. #1778
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    Quote Originally Posted by sambb View Post
    that'd be unreal. let us know when IPRA comes to SMSP. A friend of a friend may be running a Clio 182 that he's just put together and I'll be curious if the little mk2 escort turns up that had its engine built by an engine shop near me.
    The Escort is entered for Wakefield, goes good in a straight line, doesn't stop all the great and doesn't handle at all. Like all leaf spring/live axle cars he needs to spend as much on the rear end as he did on the engine, then it might be half OK.

    Round 2 at SMSP is 3/4 April.

    Cheers
    Gary
    Golf Mk7.5 R, Volvo S60 Polestar, Skyline R32GTST

  9. #1779
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    Cool I'll see about getting along to that round.

  10. #1780
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    Not heading to Ringwood this Sunday for a shakedown before Bathurst Sam?

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