8v cylinder head porting with flow test results

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

  1. mr hillclimber Club GTI Supporter and Sponsor

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    Tut Tut! lol! :lol:

    Thanks. No I dont think its the bench, I do check some things a couple of times over to try and catch it out and the results are always within 1/2 cfm or less... big changes appear to mean just that, and the following test with the manifold (which you'll see soon) followed the same trend.
     
  2. mr hillclimber Club GTI Supporter and Sponsor

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    Oh I think we could have a chat about that....[:^:]
     
  3. mr hillclimber Club GTI Supporter and Sponsor

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    :lol: I've also got that BPF on the 16v for you Neal, I update the relevent thread as time permits.
     
  4. mr hillclimber Club GTI Supporter and Sponsor

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    Right... to get this finished to date we need some flow data with the DCOE inlet manifold fitted. I'll add them both in here for simplicity, but not sure how it would be best to juggle them in the chart... I'll leave that headache with you Mike!

    The first set of results are the "D+" head with the manifold ported as per it last ran. In that configuration it made circa 177hp, so that'll give you some sort of idea to compair flow to power, BUT, it's NOT a hard and fast rule... I've seen engines make big power with a lot less flow than is the norm (Ford Pinto), but we need some form of decent airflow to produce some form of decent result.

    The second set of results are the final JMR spec head as it will run.

    Anyway... here goes...


    .050 13.6
    .100 26.5
    .150 40.8
    .200 54.9
    .250 66.4
    .300 76.6
    .350 79.8
    .400 78.5
    .450 81.2
    .500 82.4

    And this final set of results on the JMR porting spec also includes extra work to get the best from the manifold, though I also did the original on the D+ above, though with the bigger port size I had to re-work the manifold more.

    .050 17.0
    .100 32.7
    .150 47.2
    .200 62.2
    .250 75.0
    .300 84.1
    .350 84.3
    .400 85.7
    .450 88.6
    .500 87.6

    As can be seen, the manifold knocks a fair bit off the top end of the flow on the D+, with some smaller losses at the low end. After re-working it some more, the low end results on the JMR head are more or less the same with or without the manifold up to .250, with an increase with the manifold at .300 & .350, but the losses return at .400 and above, though less than before.

    The above shows the importance of getting the inlet manifold to flow on these heads (imagine how poor they are off the shelf!), and also how improvements can be had over the percieved best with some detail size correction work.

    We now have some good flow gains over the starting point, though these manifolds still cap back the top end flow. Flow above .470 thou lift is'nt important in this case as thats the peak lift of my cam, but further cam development will be hampered by the heads top end flow ability (the flow at .550 dropped from 97.8 to 89.7 on the JMR head with the manifold fitted), or at least with the DCOE style manifold, due to the spacing differences between the carbs and the head ports... a part cure is in the pipline.;)

    Thats it as far as this project is concerned. I have some flow figures from another head with 42mm inlet valves & a race Ford "Kent" crossflow to post up, the results may surprise you. And there's the exhaust side to come next, though I've yet to port one on a standard 33mm exhaust yet, may try and knock one up asap after other work is clear.
     
    Last edited: Nov 25, 2009
  5. Mike_H Forum Addict

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    Updated the spreadsheet (at last). Can you check I've made sense of the last couple of columns? I wasn't 100% sure which head you were running. If you want any changes, just let me know.

    [​IMG]
     
  6. mr hillclimber Club GTI Supporter and Sponsor

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    Looks good to me Mike.

    Maybe define the last two columns in a darker or lighter tone?

    Just to confirm... the last two results columns are the big valve head, the first test is as it came to me but with the DCOE manifold that I ported and opened out the inlet ports to suit.

    The second set of results are after I re-ported the same head to my spec with some additional manifold porting to suit the new port size in the head.

    You can compair columns 3 & 6 (the pack D spec with & without manifold) and 5 & 7 (my final re-ported version with & without manifold). All other results are bare head results without a manifold.

    Many thanks to Mike H for his help in making some sense of the results and compiling the chart.... thanks Mike.
     
  7. Brian.G

    Brian.G Forum Member

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    This is quality , QUALITY.
     
  8. alexisblades99 Forum Member

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    great stuff.

    mr h, if say someone totally inexperienced in head work was to have a go using your previous guide, how much of a variation from your above figures could he expect?

    would you say it's one of those skills where you've got to be especially precise, or is there a bit of a margin for error?

    ie: an amateur could improve the flow in his head, but it wouldn't be quite as good as a pro job?

    or: could an amateur very easily completely stuff the head if he isn't exactly spot on?

    is it possible to actually make the flow worse than standard with a slip of the die grinder?
     
  9. Tristan Forum Junkie

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    YES![:$]
     
  10. mr hillclimber Club GTI Supporter and Sponsor

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    As Tris said above... yes indeed. It takes a certain amount of finesse, so I say try a bit of a practise run on a scrap head, any make will do, to give you an idea of how the cutters remove material, the sort of pressure you'll need to apply, that sort of thing. The same with the use of the flap wheels.

    The variation can be between 'nothing to worry about' to 'buggered'!... as above really, apply caution and 'feel' your way into it. You should be able to achieve a good working result if you follow the guides, remember though... once you've got one port finished, you then have to do it 3 more times for the inlet, then all over again for the exhaust!

    One thing is for sure, once you've done your own head, you'll understand and appreciate the amount of work that goes into it to do the job properly! :lol:
     
  11. Tristan Forum Junkie

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    anything to report Jason?
     
  12. mr hillclimber Club GTI Supporter and Sponsor

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    What'due wanna know?

    I must post up the exhaust flow results for the hillclimb head, and get around to porting an exhaust on std valves.

    There's an 1800 8v hillclimb engine going on the dyno soon on t/b's & DTA.
     
  13. Tristan Forum Junkie

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    the exhaust flow would be interesting .
    See PPC mag this month , Dave Walker porting a CVH? He reckons its all about shape , leaving a rough finish makes no difference... Whats your opinion?
     
  14. mr hillclimber Club GTI Supporter and Sponsor

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    Thats true, shape is the important thing the achieve. Tho it depends on what's ment by rough... I would'nt leave a rough cut burr finish myself, but if done tidy, even that would'nt be a big problem.

    As soon as I have enough time to put it into order I'll get the exhaust results up.... trying to juggle doing it as well as talking about it can be a difficult compromise at time! :lol:
     
  15. Axewielder New Member

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    so have you tried with a lathe+ how do you get repeatable results with the drill+ grinder method?
     
  16. Axewielder New Member

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  17. Rustynuts Forum Member

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    Very interesting read this, are there any different rules or results to think about for 8v heads using forced induction? In my case G60.
     
  18. simonmk2 Forum Member

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    After reading this thread i've had a go at porting my own spare head and the amount of fidly work needed and time that goes into it is loads, I think you need a medal. Why on your eairler guide did you do a compression test with the burette? and how did you get the very polished finish on yor ports? i used a bit wet n dry on a split rod 240 which leaves few faint scratchs, would it make much difference if it isnt mirror perfect like yours?
     
  19. mr hillclimber Club GTI Supporter and Sponsor

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    Practise makes perfect....

    All you really need to do to break the sharp edge off the seat to the back of the valve, the angle will be approx 30 degree's.
     
  20. mr hillclimber Club GTI Supporter and Sponsor

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    We built our own bench and use a hardware/software package from America that does the number crunching, the same as Superflow use on their benches.

    Thats quite a good book, some good basic ideas and dimensions. The flowbench stuff is a little complicated though.
     

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