High power big power 8V exhaust manifold?

Discussion in '8-valve' started by Jon Olds, Jun 21, 2019.

  1. Jon Olds Forum Junkie

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    Title should read High Power Big CC .....
    Going to build a big 8V based on the Eurospec 42/35mm head I have recently acquired.

    Couple of things that the clubgti knowledge base could answer;

    Availability of a big bore exhaust manifold. The port is real big, so I need a manifold at least the full size of an exhaust gasket. What do people use? (Mk1 or mk2, not sure of the application)

    I have bought a double weber inlet manifold that needs port matching? Who is good?

    Thinking twin 40 , 42 or 45 jenveys. What'll suit a GS6 cam with 12:1 com?

    Anybody got any bits that may help me out?
    Jon
     
    Last edited: Jun 24, 2019
  2. HPR

    HPR Administrator Admin

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    Will it be a 1.6 or 2.0 engine ?

    A GS6 cam sounds me bit heavy... with 316 duration and 101 degr LSA and lots overlap...
     
    Last edited: Jun 21, 2019
  3. Jon Olds Forum Junkie

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    It will be 2L or slightly over if I go for a rebore. I run a GS6 in my full race 1600 EG and it is 'heavy', like a sledgehammer..

    So, I was thinking of downcamming the 1588 to 276 degrees, 11.3mm and 2.5mm at TDC , as an experiment (have a schrick cam already) and trying
    it on the rollers. It is hasn't lost too much at the mid/top end, using the GS6 in a 'big' motor where it should be less 'cammy'


    Jon
     
  4. Jon Olds Forum Junkie

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    Last nights brainstorm was to use the short ABF flat top pistons in a long block 8V. Gudgeon pin is the same diameter. But I think I will have too much CR.
    Looking to lose 10cc from the volume above to get the CR up on std parts. (560/60 to 550/50 if that makes sense). So now thinking a 2mm block skim and a little bit of piston shaving instead
    Jon
     
  5. HPR

    HPR Administrator Admin

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    To get 12 /1 CR on a 2 L > 496 / 11 = 45 cc
    OR 496 + 45 = 541/45 = 12

    So indeed, it will need either a head skim
    OR skim block and machine a dome onto the piston
    OR skim a bit of both > head and block
     
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  6. Jon Olds Forum Junkie

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    Block is away getting 1.5mm off the top, I will skim the pistons so they protrude 0.75mm or maybe 1mm which will also
    shrink the bowl volume a small amount.
    There's not a lot of material before the top ring to play with.
    Pondering whether to shorten the skirts also 10 or 15mm, they are a long piston.
    It'll be a real budget short engine, if this all works...
    As usual with VW's (that have been serviced...) the crank is mint...
    Regarding throttle bodies, my gut feeling is that 40's should be enough, although I'm very open to comment on this.
    I know bike engines massively oversize theirs
    Jon
     
  7. HPR

    HPR Administrator Admin

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    As a 2 L 16V on 45 mm and a 1600 16V on 42mm trottle bodies can make very serious power levels ..
    If we go from 45 mm or 15,9 sq cm, if we take 80% of that = 12,7 sq cm > thats 40 mm ( 12,56 )
     
  8. Jon Olds Forum Junkie

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    Thanks. Biggest chokes for 45dcoe is a 40, so not having any choke............
    Any thoughts on shortening piston skirts?
    Jon
     
  9. HPR

    HPR Administrator Admin

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    As the ventury is relative short in lenght within a 45 mm carb housing + trumpets…. it might give not to much restricion…

    On make a shorter piston skirt ...10 - 15 mm sounds me much… as the piston get less guided in bore > piston slap...
     
  10. Tristan Forum Junkie

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    All interesting stuff though Jon. Are forged pistons completely out of the question?
     
  11. Jon Olds Forum Junkie

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    No, its just I've got 6 race engines and my wages wont stretch forever.
    I'll take some pics and post them, the ABF is really short, these 8V ones must be Victorian, the skirts are that long.
    There is a 'natural' internal rib that I will skim up to, I think. About 9mm off, I will post up some pics.
    Jon
     
  12. Jon Olds Forum Junkie

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    Other cams in 'stock' GS2 (too mild), GS3 (prob right for a 1600) and some wacky schrick thing that someone may recognize gs3 alonside bumpy schrick.JPG
    comment on please, as above;
    Left hand one is a GS3 (base circle 36mm , presumably std) Lobe max 47.7, so 11.7mm lift
    Right one is a flat topped shrick monster thing. Base circle 38, peak 49.2 so 11.2mm lift

    Does anyone recognize this as a slick 50 special? Or what? It must have a monster area under the curve. Ive labelled it as 314 deg duration, cant remember why...
    Jon
     
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  13. Jon Olds Forum Junkie

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    Also piston skirt comparisons;
    abf skirt compare to 8v.JPG
    Left one is 8v compared to ABF on the right
    abf skirts inside.JPG
    Must be able to skim the 8v one down, possibly to that natural step?
    Comments, as always, appreciated
    Jon
     
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  14. Tristan Forum Junkie

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    Can't see why not, you're not revving it to.the moon or expecting it to do 100000 miles.
     
  15. Jon Olds Forum Junkie

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    Its a 'long stroke 8V so it'll be about done by 7500 I'm guessing. Probably do 1000 miles ......... in about 6 years.
    LOL
    Jon
     
  16. HPR

    HPR Administrator Admin

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    As you talked about ABF pistons in post 4 …. i tought you would use these , not 8V piston

    GS3 cam is the way to go > 300 degree / 102 LSA / 11,6 mm lift
     
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  17. Jon Olds Forum Junkie

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    Thanks, I have misled you, the 8v pistons can have their 'Victorian skirts' trimmed a bit, I think.
    Agree a GS6 is a bit OTT for a 1600, so I will fit the GS3 and visit the rollers again. Interesting
    to share the results on here.
    Any idea what that lumpy schrick is?
    Jon
     
  18. HPR

    HPR Administrator Admin

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    8V piston can indeed trimmed till that ridge inside or even a bit more.... it doesnt need to do lots miles

    Even for a 2.0 L engine the GS3 would do very well...
    Often engines get cams who are OTT , just get a good overall performing engine that is strong from below...
    I have no idea on the schrick cam...
     
    Last edited: Jun 25, 2019
  19. Hot Water Forum Member

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    What fuel are you running with 12.5 CR?
     
  20. Jon Olds Forum Junkie

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    Best pump fuel, only, UK, nothing special.
    Doubt i'll get as high as I want it
    Jon
     

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