8v cylinder head porting with flow test results

Discussion in '8-valve' started by mr hillclimber, Nov 8, 2009.

  1. Mike_H Forum Addict

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    Excellent stuff, Mr H - really separating myth from reality here. Hopefully the end result on the dyno will back up the flow figures!
     
  2. Tristan

    Tristan Paid Member Paid Member

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    Hats off to Mr. HC.. he could easily have kept the hard data to himself and just sold the ported heads . Fair enough , not many of us are gifted enough to reproduce the gains ourselves using his guide , but even still...

    Mr HillClimber..the Main Port runner.. is that the section of the head from inlet manifold inward?
     
  3. mr hillclimber Club GTI Supporter and Sponsor

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    Cheers Chris...

    I could tell you now, but I'd have to shoot you!...... 90CFM of inlet flow, or in fact a bit less is enough for....... the answer will be a bit later in the thread!

    I have flow data from an ex slick 50 head with 41mm inlets from an engine with known power output, and the same head after a bit of re-porting. Big valves dont always do what you think, unless the porting is done to suit. And it is VERY easy to improve in one area and loose in another with a simple change... stay tuned for all of the above.

    I have my own theory on that one Chris (the standard port & polish job) but I feel a bit reluctant to reveal it... there is in fact a clue (though unintended) in the above paragraph.
     
  4. mr hillclimber Club GTI Supporter and Sponsor

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    Thanks Mike.

    This head is currently a test "mule", though it's likely to turn into a new race head when finished... mine actually, but there's more to come yet.

    As above, I have dyno data from the engine I built last year with similar inlet flow to the above (remember we hav'nt touched on exhaust flow yet) which could give a good guide to potential, which I'll cover later in this thread.

    I will have easier access to a..... power measuring device.... early next year, in fact a couple of different versions, which will make seeing how the power stacks up interesting. I can use an engine dyno anytime, but setting up K-jet or O.E Digi would be a pain, unless someone wants to pay my dyno man 300 quid a day plus setting it all up... I'd be quite happy to swap heads around then!... though a dyno mule engine on carbs maybe an option.
     
    Last edited: Nov 14, 2009
  5. mr hillclimber Club GTI Supporter and Sponsor

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    Thank "you" Tris...[:$]

    You have all the info to date I have found, but yes, your spot on in your comment re the reproduction side. In the last test (to date) on this series of head mods, I'll show you how a small change can alter the flow curve... so someone else trying to reproduce the exact set of results can easily change the outcome with a slip of the die grinder, though if you combine this thread with the "how to" guide in the sticky you can produce a good working result.

    And yes, what I call the main port runner is the straight-ish section fron the manifold face to the guide boss / short side turn area.
     
  6. vw_singh Events Team Paid Member

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    When are you posting the next chapter? I'm on the edge of my seat! :thumbup:

    Gurds
     
  7. Mike_H Forum Addict

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    I've read that work on the short side radius to reduce the sharpness of the turn, can make a big difference to the flow. Is that in your plans?
     
  8. mr hillclimber Club GTI Supporter and Sponsor

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    Mike... the 1st mod with the basic throat work also included blending the sort side turn, so only a couple of CFM for that work. The standard short side is'nt too bad, the basic shape is there, it just needs blending.

    Gurds... :lol: .... just for you, here's the next, and last current stage of inlet mods.


    As I was just about 2 CFM away from my total (90CFM) goal I had a measure up of the whole port & throat and figured a final small increase of the throat and venturi below the seat may give me what I was looking for. Well, there were indeed changes to the flow, but not quite what I was looking for...

    .050 15.7
    .100 30.0
    .150 45.1
    .200 55.9
    .250 66.1
    .300 75.6
    .350 79.3
    .400 83.0
    .450 87.0
    .500 85.7

    As you can see, we had some small losses at the very peak of flow, but some bigger losses in the .350-.400 area (told you you'd get warts and all!), though there are some improvements in the lower part of the flow curve up to .300... who said head porting was easy!

    What the above shows is that it's very easy to "rock" the flow curve by making a simple change... all I did was increase the throat & lower seat area & blend the seat.

    The last flow curve is still a fair bit better than where we started, but overall it's a little down percentage wise over the previous test, so a mod too far maybe?... well, thats development, if we did'nt try it we'd never have known.

    As for the goal I was aiming for... I later went back and checked a result that was achieved on one of these heads by no less than Dave Walker (Emerald ecu's) when he was porting a lot of successful heads. On Dave's flowbench he had a baseline of 76CFM on the head he tested, with a final tally of 90CFM, so a gain of 14CFM (18.5%). As I had a starting point of 71.5 I've managed to gain 16.4CFM of extra peak flow (23%) to give the 87.9.

    So I'm happy that we're in the right ball park but is more possible?

    Well the next step is to try a slightly bigger valve (40.5) as this is used in some "big valve" conversions, and I'll be removing the guide boss compleatly. If time allows I'd also like to try and turn down the stem from 8 to 7mm to test that mod on its own, and maybe just an increase in the head size to 41 or 42mm and leave the port/throat size as is to see what happens there.

    I also plan on doing the above test in reverse as I'm not yet convinced that opening the port alone is worth almost 10CFM... I think if done on it's own, all that will happen is a small change at best until the throat and seat work is carried out, so dont go hogging out just the port runner alone expecting an easy ride.

    Hope you've enjoyed the ride so far.

    The next chapter is.... how well does the "road" spec head stand up to a renowned race spec item... and is it possible to gain more flow from the same race head without changing the valve size...and, what happens when we add a DCOE inlet manifold... the plot thickens... results soon.;)

    [​IMG]

    [​IMG]

    And above are were we are to date. The finish is'nt perfect as it was just for testing, though shape is far more important than anything else.
     
    Last edited: Nov 15, 2009
  9. vw_singh Events Team Paid Member

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    Yay! A nice read from the start. I like the way you show the effect of each step.

    As you say, you seem to have achieved the same gain albeit a lower cfm figure.

    How does your technique and theory translate to the 16v head? i.e the inlets at 82% and valve seat at 95% of the inlet valve etc...
    I got one that might give a go [:$]

    Gurds
     
    Last edited: Nov 15, 2009
  10. alexisblades99 Forum Member

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    excellent stuff, mr h.
    so do you think this sort of thing can be attempted at home without making a proper fist of it, or is it best left to the experts?
    also any plans in the pipeline to look at flow rates for the different types of manifolds?
     
  11. mr hillclimber Club GTI Supporter and Sponsor

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    Thanks...

    The 16v can generally be a little smaller, though I'll go ino that at some stage when I doo all this again but with a 16v head. If you follow the basics though in the mean time you wont go far wrong.
     
  12. mr hillclimber Club GTI Supporter and Sponsor

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    You can indeed. Tho making a "fist" is it is how good you think you can control yourself (oo-err!)... it needs a fair bit of finess & measuring.... check, check, and check again before you go grinding, it's not so easy to put it back on!

    Yes, in fact coming up soon is a race head, before & after porting, with & without a DCOE manifold. I also found a K-jet manifold which I'll try on this "mule" head so we can see how much flow we loose... no idea on the answer to that one yet, as soon as it hits the flow bench I'll get the results up.
     
  13. 50ftdubdemon Forum Member

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    result that has me most confused is when you tapered off the valve guide.. flow curve really suffered between .25 to .35 and never really recovered until you opened up the main runner. even then there seems to be a bit of a dip at .3

    can see from pics youve done proper job shaping the thing (serious skills with the grinder :thumbup: ) so maybe its to do with increase in cross-sectional area? ie the air is slowing and creating turbulence?? might get more of an idea when you take the boss out..
     
  14. Mike_H Forum Addict

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    Keep up the great work!

    Have you got a Mk2 digi manifold to compare? I guess that would be of interest to a lot of folks reading in. I'm happy to send you a spare one if it'll help.
     
  15. Mike_H Forum Addict

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    I thought it might be interesting to put all the results side by side, although I daresay if you did the mods in a different order, you'd get different results. It would be interesting to see.

    Mr H, if you want the spreadsheet, so you can add the next sets of numbers, or if you want me to add anything, let me know.
    [​IMG]
     
    Last edited: Nov 17, 2009
  16. drunkenalan Paid Member Paid Member

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    still on standard size valves... i cant wait to see what happens with bigger ones.

    good work Mr H, and keep it coming, please
     
  17. Tristan

    Tristan Paid Member Paid Member

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    3 angle seats don't do a lot , do they ? why then does every head builder always insidt on doing them in modded heads?
     
  18. mr hillclimber Club GTI Supporter and Sponsor

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    "You" were confused! :lol: ... I do plan on doing these mods in reverse and will be leaving the guide tapering till last. Certainly will be interesting when the boss comes out.
     
  19. mr hillclimber Club GTI Supporter and Sponsor

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    I think I may have Mike, but I'll shout if I get stuck for one.

    And the chart looks great, thanks for that... I could'nt figure out how to post one up so a top job. And your about spot on with the application split. I'll post up the race head figure soon, so if you could add those in that'd be great.
     
  20. mr hillclimber Club GTI Supporter and Sponsor

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    Cheers Alan... get that engine running!

    Tris... I was a surprise to see it too. I know many successful head modders who blend the lower seat cut out, so in effect loosing the bottom cut. and they seem to work fine, some keep the agles, others dont.
     

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