Porting plans 12G202 and siamese port anatomy

Based on remarks from Mr Erland Cox about getting 90 degree ports to work I have started to plan some mods for the 12g202 head.

The way they tackle it with volvo heads is to extensively weld the port and build material. As this is pretty much impossible with this head ( welding cast iron is very involved and there is not much room to work). It is possible to add epoxy to the port to build up the ssr but while people have done this a lot ( apparently z spar -splash zone is the one to have) I’m not 100% convinced that it will hold for road use.

Port anatomy

So how can you improve the head  when you can’t add material. The cross sectional areas are odd because of the comparatively huge volume of the siamese section. I think that one way to look at the port is to divide it into sections.

First section is a straight round port. This section then expands into a small plenum with a nice a gradual exit. Then into another very short port. This this way it is very much a manifold including the port- to- port interaction.

The interactions between these three ( 6 with the cylinder and the manifold) volumes are very complex and I for one will need a whole lot of hard thinking ( gimme a year or two) to even start how to ”solve” this. Luckily, and I quote  ”using the Newton- Raphson method for solution for solution of multiple polynomial equations and handling the matrix arthimetic by the Gaussian Elimination method the additional computational complexity is negligible”. Wel no worries here then  😉

Even then I think looking at the port as a manifold rather than a weird port makes more sense.  Using the resonance to the get the other port started seems like an interesting idea.  But first the port and how the get the air around the corner.

The basic premise is that the SSR ( short side radius) is never going to work because the radius will be too short whatever you do to it. The idea is to initiate the turn right at the face of the port and try to remove minimal metal ( there is not all that much to cut anyway. Rather than raise the roof on the port the entire way I’ll try just raising it somewhere in the roof of the siamese section. The SSR has to be foreshortened. I hope in that you can utilize more of the valves circumference at higher lifts and port speeds and give up some low lift flow.

green is the proposed modification, reddish the original profile

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3 thoughts on “Porting plans 12G202 and siamese port anatomy

  1. the way i look at it is ,

    the air flows into the left valve ,then the right .

    the flow pattern therefore goes something like this .

    left valve (lv) opens ,any inertial ram and harmonic ram occurs to help overcome reversion ..mixture flows into cylinder, pulse travels up pipe to air/bellmouth interface then reflects a positive pulse back .
    inertia ram starts to build energy as the port flows more and more and the tube of air builds momentum .
    port reaches max velocity ….area over right valve (rv)creates an eddy .
    port starts to slow ,valve appraoches closing point .
    inertia in port is high and any harmonic may or may not be arriving at the right time for the rv to start to open .
    rv opens , the environment is now quite different to that for lv .
    the inertia of the tube of mixture heading into lv is still very active ,so rv gets a much much high mass flow rate upon openning that lv .
    the fuel cannot change direction as easily as the air so the first package of mix into rv is not only much denser ,but also much leaner .
    so now we have rv with the inertial column of air built up by lv being force fed inot rv plus any harmonic that is timed correctly from the shutting of lv and the openning of lv affecting things .

    this overcomes the plenum effect of the joi in the head reducing the port velocity ,and pushes rv inot a far igher ve than expected .this explains the 100 hp/litre achieved by the 5 port head .

    the rp is now open fully …the cylinder is much fuller than the lv ,so the comression ratio is also now comensurately higher ,therefore coupled with the leaner mix det is much more likely . offestting this is the airspeed in the port, due to supercharge effect from lv means the incoming charge is cooler than lv since it has not been sitting in the head for as long .

    we now have an eddy in the area above lv .

    now the rv starts to close ,any harmonic now comes into play alos there is built up inertia .

    the rv closes ,and the inertia starts to bang on the valve backs ,but has to wait until the lv opens again so becomes dissipated .the harmonic from rv closing also dissipates to a certain degree .

    phew ! all the above is imagination not scientific fact .


    • mowog says:

      sounds about right..
      somebody should be able to do a CFD simulation using the pulses generated by the valves opening and closing of the valves and the pulsing intake flow.

      Cheers Joost

  2. […] have covered this a bit here. The majority of gains are made in the part about 20mm above and below the […]

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