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Thread: Sams Polo 3.0

  1. #231
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    valves are :
    inlet - 3 x 27.35mm roughly
    exhaust - 2 x 29.87 roughly

    I had a link to a site where they'd compared the cfm of the large port head to small port heads and I remember you saying at the time that the head was heavily biased towards excessive exhaust flow relative to inlet flow. I know in the past i've seen it said that if there is a high EGT issue then its most likely due to restrictive exhaust manifold and/or turbo sizing on theses engines but not likely from an under done exhaust valve/port from the head itself. Hopefully thats true. On the inlet side, the inlet valves are the same whether you have the small or large port head, its just that the large port head has just that, larger ports and does flow more due to that. So by going large port I have swung the inlet to be more balanced against the high exhaust flow but still the head is over exhausted from OEM.
    Sams Polo 3.0-lp-jpgLP vs SP. all valves common. combustion chamber common. only the inlet port size varies. LP inlet cfm at 50 thou is higher suggesting a port restriction on the sP head.

    The OEM head is fastened with stretch to yield bolts. Not sure if ARP do bolts too but they do do ARP studs.

    Good call re the sodium filled valves maybe carrying more material to compensate for the infill and maybe actually being heavier. I'll try to find out what the weights are of OEM vs Supertech stainless.
    If I have a cent left over for the head, it'll either have to be valves or ARP head fasteners but not both. Anecdotally it seems to be that that exhaust valves are seen as more of a reliability issue than OEM head gaskets/ head fasteners but i'll need to obviously detective out which is the bigger potential issue.
    Last edited by sambb; Yesterday at 06:46 PM.

  2. #232
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    cam cover breather thoughts:

    Sams Polo 3.0-img_2485-jpg
    The breather port is 18mm diameter. (AN12) That's an area of 254mm sq.
    Sams Polo 3.0-img_2484-jpg
    It is fed though by these holes in the oil/air separator plate. They are 6 x 6mm di holes = total area 28.3mm sq x 6 = 170mm sq. Thats a single pipe equivalent of about 11mm di = AN7 if it existed.

    So either the area of the baffles holes is correct and the outlet pipe is 33% too big OR the outlet pipe is the correct size and the baffles are 33% too small. I'm thinking that the outlet pipe is correct for a modded engine and that the baffle plate needs to be brought up to match the pipes flow capability. I've worked out that 3 more 6mm holes in the baffle plate ( 9 in total) will give it input flow to match the outlet pipe to the catch can. Thoughts?!
    Last edited by sambb; 12-10-2021 at 12:51 AM.

  3. #233
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    Can I just confirm the valve sizes;
    3 x 27.35 = 1763 sq mm
    2 x 29.87 = 1402 sq mm
    Based on the above the total exhaust valve area is 79.5% of the inlet valve area. Which is pretty damn close to the 80% rule of thumb minimum I like to use.

    On a $value basis head studs probably rate higher than an exhaust valve upgrade.

    Cheers
    Gary
    Polo GTi 2017, Golf Mk7 110TSI Highline, Golf Mk7.5 R, Skyline R32GTST, Stagea RS4,

  4. #234
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    The principle of a cam cover breather is to slow down the air speed of the blow by to give time for the oil mist to separate from the air. Having a smaller area of breath through in the baffle plate than area of the outlet fits that principle. What's inside the breather void? I use Scotch Bright stainless steel scrubbing pads to slow the airflow even more and to help the oil out of the airflow.

    Cheers
    Gary
    Polo GTi 2017, Golf Mk7 110TSI Highline, Golf Mk7.5 R, Skyline R32GTST, Stagea RS4,

  5. #235
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    Hi Gary,

    Jeez I was definitely under the influence of shift work when I was looking at valve sizes. I only forgot to calculate area!! ha ha.
    I found the official supertech std valve sizes:
    inlet 26.90mm x 3 = 1705mm2
    exhaust 29.90mm x 2 = 1404mm2

    exhaust is 82% of inlet which is even a bit better than first calculated by you when I was just trying to jam verniers in there.


    RE the breather, I was just concerned that 6 x 6mm di holes which I think came out at -AN7 equivalent (if put in terms of a single pipe) was just not enough flow area. If that looks to be ok I'll leave it alone. Basically that plate goes into an empty cavern that the exit pipe is pressed into. I could get steel wool in there but only through the exit pipe itself as the baffle plate fixings have been peened over and would need to drilled off for access and then re-fixing it doesnt look to be straight forward.

    Re head bolts vs exhaust valves I was thinking that a blown headgasket can always be sorted if it happens but a dropped valve is potentially terminal, so I was leaning more towards valves. But I think there's a high chance it'll just go in as is because of dollars or a lack thereof.

    I'm not even sure the AGU golf large port inlet mani will fit in the engine bay because of its different throttle body angle so i'll have to do some fab mods there that will require IPRA Andrew doing some more welding for me, so i'll need to hold some money in reserve. But yeah if I discover some money then the head bolts vs exhaust valves thing will start to make my head hurt.

    thanks for your help Gary.
    Last edited by sambb; 12-10-2021 at 09:10 PM.

  6. #236
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    I think you have it pretty well thought through Sam. I should mention that's it's unusual for a turbo car to blow a head gasket and not cause other damage, commonly to the head itself or the deck of the block. With NA cars we can often get away with a quick gasket swap, but a turbo car we are rarely that lucky.

    Cheers
    Gary
    Polo GTi 2017, Golf Mk7 110TSI Highline, Golf Mk7.5 R, Skyline R32GTST, Stagea RS4,

  7. #237
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    Hmm ok good point. Ok Ill have a quick squiz at ARP bolts vs studs tonight and get some part numbers and prices.

  8. #238
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    just got a response from super tech. AEVN-1103 supertech stainless, stock diameter, triple groove keeper exhaust valves are 43.9g each.
    Now to find out what a stock one weighs. anyone?

  9. #239
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    just found this. A cool aussie designed/made flat slide jet/needless carby.

    Rotec TBI how it works...50 off 0.03mm jets! - YouTube

    would go great on a little Ford Escorts Pinto....... just need the $30k for the car first!

  10. #240
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    Quote Originally Posted by sambb View Post

    RE the breather, I was just concerned that 6 x 6mm di holes which I think came out at -AN7 equivalent (if put in terms of a single pipe) was just not enough flow area. If that looks to be ok I'll leave it alone. Basically that plate goes into an empty cavern that the exit pipe is pressed into. I could get steel wool in there but only through the exit pipe itself as the baffle plate fixings have been peened over and would need to drilled off for access and then re-fixing it doesnt look to be straight forward..

    Don't forget Sam, the cam cover isn't the only exit for crankcase pressure

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