HP gains from just a valve job?

Discussion in 'High Performance Modifications' started by need-for-speed, Oct 17, 2017.

  1. myu

    myu New Member

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    Dec 9, 2017
    Ticino, Switzerland
    In my opinion, a 3 angle valve job create more power for two main reasons:
    1) you have modified the total timing of intake and exhaust: they "open" earlier, and they close "later" ( ---> the opening and closing timing is done by the camshaft, but the angle job increase the opening/closing time, so you have more 'gap' ---> more flow for the same lift)
    2) more flow because the pipeline had now a better design.

    I'm pretty shure that a good valve design affected the resonance inside the intake/exhaust pipeline, assuming that those pipelines are from the end of intake manifold to the 'top' of the valve, and from the exhaust valve top to the start of the exhaust manifold. ( chosen because the 'change' of section)
    [​IMG]
    [note: velocity, area, vol, and length are metric..]

    that's formula for helmholtz resonance, that's pretty good for dinamically supercharge any engine (peak of 14 psi in rallyes airbox).
    Anybody had done some math about that?
    Pro, cons?

    Myu
     
  2. camaro71/holland

    camaro71/holland Veteran Member

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    Aug 27, 2003
    The Netherlands
    Must say that I don't understand and/or agree with your first point. Can't see the connection between a valve job and opening/closing time of a valve.

    What you can achieve, is improve the ability for the mixture to turn around the valve. Air doesn't like to turn more than 15°. Hence the valve/throat angles of 30/45/60 degrees....

    Too much work to seat can lead to vale sitting too deep in the seat/head and hurting flow.

    Just to give an idea where most gain can be achieved = where the effort should go to and in what order:

    0210hpp_flow04.jpg
     
  3. myu

    myu New Member

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    Dec 9, 2017
    Ticino, Switzerland
    thanks for the schematic, pretty interesting.

    what i mean, in the first point is that an angle job at the same lift increase the total area were the air/fuel mix can cross, so quite similar to a bigger duration cam. of course the opening/closing timing is given only by the camshaft (as mentioned in the previous post).


    for the 15° gaps i trust you ( when a thing work: it works.), but i'm pretty shure about resonance (and coanda: that's one could explain your 15° 'gap') effects.

    (--> excuse me for some errors in the language)
     
    Last edited: Dec 10, 2017
  4. camaro71/holland

    camaro71/holland Veteran Member

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    Aug 27, 2003
    The Netherlands
    I think here it is where you make the mistake. By performing a valve job, you don't chage the area the mixture can pass.
    You simply improve the path for air/mixture it has to pass.
    Like I said before, 15 degrees is the max air will change in direction. Thst's why you see the common angles change by no more than 15 deg. When you undercut the valves, you grind part of the valve to 30 deg, because it goes over in the valve seat which is 45 degrees, a change of....
    But you don't enlarge/increase the area. You can only achieve this at the valve, by putting a bigger valve in the head.
     
  5. myu

    myu New Member

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    Dec 9, 2017
    Ticino, Switzerland
    [​IMG]
    Just taken that picture from google (credits: john maher racing)

    If you cut (keep it simple) a 30° on the top of a valve (backcut right?), and you don't add material to te seat of the valve, you increase automatically the area where the flow can cross (the seat in this picture i suppose is the same 45° as the middle angle job): where you have done the cut simply you have removed material, so when the valve is pushed you don't have a 45° valve angle on 45° angle seat surface, but a 30°angle on 45°. so that it's a difference in volume -> difference in cross area for the flow.
    the diameter at the top of 30° is not the same if the angle was 45° (as in origin).
    that modifiy the pressure/vacuum diagram of few deegres in opening and closure drop.
    with a seat on 60° opposite to the 30° backcut, same stuff, section area increased for the same lift.

    [ finally a forum where we can talk about engine improvments from the concept how do the job! thanks!]
     
  6. Mwilson

    Mwilson Veteran Member

    does not change the timing it does change air flow at given lift
     
  7. myu

    myu New Member

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    Dec 9, 2017
    Ticino, Switzerland
    and what about hollow valves with/without (already seen empty on admission !!) sodium? never head on sbc, but pretty good for high revving engines..
     
  8. 1980RS

    1980RS Veteran Member

    1,670
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    Jun 17, 2006
    MN
    The hollow and sodium valves are very expensive. I have a set for my large port Vortec heads and the valves are worth more than the castings. Last I checked they were like close to $1100 with the exhaust being $98 each alone. You don't need them for the street.
     
  9. Titan77

    Titan77 New Member

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    Feb 18, 2014
    Vancouver, WA
    Thaler a look at Skip White Performance. skipwhiteperformance.com. They have a couple different fully assembled aluminum head options for under $1000 with different options for hydraulic roller or regular hydraulic lifter setups
     
    need-for-speed likes this.

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