Big valve head

Discussion in '8-valve' started by JamesB, Jul 4, 2005.

  1. storming Forum Member

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    all this talk of bigger valves can be quite irrelevent. the exhaust side of the head is the most restrictive. some tuners still use 33mm exhaust valves even in thier race heads! it's all down to the flowing and porting. don't assume you'll get more power just because you use bigger valves.
     
  2. storming Forum Member

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    also, the 1.8 kjet and digi heads have 40mm in 33mm ex as standard.


    the 1.6 gti head had 38mm in and 33mm ex
     
  3. chrismc Forum Junkie

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    [:[] really?

    Ive never ever known a tuner to advertise an 8v "race" head with standard valve sizes.

    For sure there is more to it than just whacking a bigger valve in there, but a larger valve gives more scope for porting the head. Smallish (33mm) exhaust valves on an 8v head are a traditional way of capping output as I have been told by more than one leading VW tuner..

    If the inlet side gives such gains, I wonder why all the leading tuners dont do a head with a 42mm inlet & 33mm exhaust????[:s]
     
  4. JamesB Forum Member

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    I can only imagine, simply there isn't enough room for 42mm inlet valves.
    I'v got a feeling aswell that if the inlet valves are made too big, it can actually de-tune the car as the airflow circulates on itself and slow down the flow of air.

    On another note, Philip has sold that big valve head now! Just too late off the mark as that was a very good deal!
     
  5. chrismc Forum Junkie

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    Its certainly possible to fit bigger inlets as C&R offer their top spec head with 42/35 valves....I spoke to Steve Cresswell about this head when I had my 8v & he said on their test car it pinked like mad, so had to have retarded ignition, thus negating any advantage from increased flow!!

    The seat area between the inlet/exhaust becomes paper thin & prone to cracking on a 42/35 head too [:s]
     
  6. rradogolfman Forum Member

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    on my 1600 mk1 gti (EG) engine code pack c head, 40mm inlet 35mm exhaust the valve seats are actually D shaped as there is no room for any material at all between the valve seats where the valves are at their closest point,
    this is a very rare head and only for really racy applications it does nothing at all below 2000 revs and doesent fully come on song until 5000, pulls all the way to 7500 though, its a really revvy livley little motor especially in a lightweight mk1 with the 1600 box and short stroke of the engine coupled through a lightweight flywheel its a fair piece of kit, pureley built for cainage deployment purpouses!! ;)
     
  7. VR6Will Forum Member

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    I agree with chrismc, it was only for the fact i was going to be running my BVH on TBs & its own management that i had bigger inlet valves fitted - 40.5mm, otherwise i was advised not to bother as it causes 8v engines to pink alot more.
     
  8. chrismc Forum Junkie

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    :lol: :lol:

    Revs to "Petrol Empty" I recall [:D]
     
  9. Mike_H Forum Addict

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    There's a place in Soham (North Cambs) that used to do a lot of Bill Blydenstein's work for him. Try them (as he's retired) but check prices first, and make sure you know what it includes at the price (e.g. does it include the new valves).

    see blydenstein for the address / phone number
     
  10. storming Forum Member

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    try autosprint in birmingham. they've been building race engines for years. call the man and ask him. he'll happily do bigger valves if you want them but advises against it.
     
  11. chrismc Forum Junkie

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    Id sooner go with the concensus of all the leading VW tuners rather than a guy from a company who supply heads for many different makes of car... [:s]
     
  12. storming Forum Member

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    you wouldn't listen to all equations before coming to a conclusion?[:s]
     
  13. storming Forum Member

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    i believe brian ricketts used standard size valves too. you can't tell me he knows nothing about vw 8v's.


    i'm not saying one is right or one is wrong. if you get the power gain you're looking for then great, but depending on how the head is flowed and ported it may not make any more power from using bigger valves.
     
  14. chrismc Forum Junkie

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    This Autosprint??

    Autosprint [:s]

    The people that used to advertise in CCC I recall. It goes back to my previous point..

    Why dont all the traditional "Volkswagen" tuners supply a race head with standard valves, or enlarged inlets only if this is the way forward??? None of the likes of TSR, Stealth, Autotechnik, or C&R do. Neither did BRmotorsport (now BBR GTi) or GTi Engineering.. [:[]

    I have also "been there & done it" 8v wise, so I know what works & what doesnt.....especially on a 2L block ;)

    EDIT: The Brian Ricketts heads had varying specs, but the top spec head didnt have standard valve sizes..

    BBR GTi
    Edited by: chrismc
     
  15. storming Forum Member

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    O.K. calm down. you obviuosly feel the need to be right. anyone who wants to have a 2.0 engine needs to have 35mm exhaust valves or it'll run like a piece of pooe and be generaly crap.


    i'd better write a letter to VAG and tell them their engine designers know didly squat while i'm at it.
     
  16. VR6Will Forum Member

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    isnt the first time i've heard people saying that the way forward for the 8v head is enlarged inlet valves over enlarged exhaust valves...seems strange becuase i've never come across a head built like that

    does anyone have a bench flowing results to backup their claims??
    Edited by: oakgreen88
     
  17. chrismc Forum Junkie

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    Not a need to be right no, but your advice goes against what the vast majority of Volkswagen tuners would say.. ;)

    I've had a 2L on a Pack A head, & yes it was dump!! Torquey but wouldnt rev [xx(] The mk3 GTi was only 115BHP, 3 more than an 1800, so not a particularly great engine [:^(]

    I gained 21BHP on Stealth Racings RR by going to a Pack C spec head, giving 155BHP at the flywheel. It all comes down to Valve area. This is why a 16v is so much more revvy, even compared to a Pack C head.....& why big exhaust valves work on a 2L :)
     
  18. storming Forum Member

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    dave walker did a project mk1 (1.8 dx) years ago in c&cc mag. they helped design the tuned lengths for the magnex exhaust system and manifolds on that job. the exhaust flowed something silly like 56% that of the inlet. (i'm guessing that figure off the top of my head but it was significantly lower). they used 35mm ex valves and got the flow right up but then used 42mm inlets aswell, so they still had poor exhaust flow rates compared to inlet.


    if i recall correctly the exhaust should be 85% of the inlet. this gives a 34mm optimum valve size to a 40mm inlet. in thoery. and 36mm ex for 42mm in. so beats me. can't see how 42mm inlets would be of benefit when it's the exhaust side of the head that's the most restrictive.
     
  19. storming Forum Member

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    i was never suggesting that bigger exhaust valves would not work. what i was trying to point out is that the valves won't flow more air than the ports and throats will let through. you're advice was to get bigger exhaust valves. would they flow more gas on a standard head?
     
  20. chrismc Forum Junkie

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    me neither....

    40mm inlet & 35mm exhaust seems to work best :)
     

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