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Thread: Cylinder head flow #'s

  1. #1
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    Cylinder head flow #'s

    Question for those who may have access to flow numbers for our SC heads. How much difference did you get when flowing the end ports vs. the middle port? Also, what do you use for smoothing air entry into the port?
    Quote Originally Posted by Miller View Post
    Ya thats why i tape mine down. People think its bc i dont have a moonroof seal (which is true) but its really to keep my roof from ripping off .
    Email me here.

  2. #2
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    I flew my heads after I got them all rebuilt prior to porting. I took them in and flow tested them and got just under 170cfm on the outers and 155 in the center port. This was without an intake on and the altitude was 4200ft. corrected.

    As for porting the entry of each port I do it in steps throughout the whole port itself. I use a 60 grit sand roll on an air dremel on the whole length of the port, right before the short turn/bowl area I use a 90 grit and for the beginning of the port I used 120 grit. Using this I pick up an average of 3-5 cfm (slows turbulence at a high RPM) as opposed to a 90 grit finish throughout the whole port. This is for aluminum.

  3. #3
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    So after porting, how close in percent, were you able to get the ports to each other?
    Quote Originally Posted by Miller View Post
    Ya thats why i tape mine down. People think its bc i dont have a moonroof seal (which is true) but its really to keep my roof from ripping off .
    Email me here.

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    All of the exhaust ports flowed 128 +/-1 to 4cfm. All I did to the exhaust was clean the casting marks up and make it a nice, smooth transitioned port as i did to the intakes too. I got the intakes to 185 with a 60 grit finish and then did the stepping later so I guess it would be around 188cfm. This was at 3500ft. corrected. On the exhaust I got 142-144cfm.

    So that would be about 76%. The ports are decent shaped, but the cross sectional area and the transition are terrible. Not to mention that middle port. I got about 172 on both of them.

    During the beginning of spring I found a junkyard SC head and did some experimenting with it. I cut the walls out, filled the floor in and raised it about 3/16", and widened the port. I got 260 with a 1.92 valve that I had sittin around. The port needs to be raised way up to get better numbers. It took about a week to do all of this work and it's one of those jobs that would cost around $6,000 to have done. It's actually a common price to pay.

  5. #5
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    Dave food for thought,
    I shaped a peice of aluminum to tac & weld in the S-curve wall
    of the center intake port. I only add what I could remove from the
    opposite wall. But this will help straighten port out.

    Shape a aluminum port plate for floors to raise intakes,two peice.
    tac-weld in ,blend. no numbers for this mod to give out

    Thanks Randy

  6. #6
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    I was wondering what impact the intake manifold has on port flow. Most people tell you to use some sort of areodynamic device at port entry. I understand that they tell you this because when doing cylinder heads you typically don't actually know what manifold is going to be used on the heads. This is typical of the real world and has a lot to do with marketing.

    For the SC since we pretty much know exactly what intake manifold is going to be used on the car, why not do your flow testing with the manifold on? Our manifold is, by appearances, a goofy design so it follows logic that it's impact on flow to each cylinder would be relevant to accurate flow testing.

    Just wondered if anyone has actually done this kind of testing...
    Quote Originally Posted by Miller View Post
    Ya thats why i tape mine down. People think its bc i dont have a moonroof seal (which is true) but its really to keep my roof from ripping off .
    Email me here.

  7. #7
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    I've done a decent amount of heads that an open plenum intake design was used on and there wasn't any change in CFM rating. Only intakes i've seen affected by it was intakes with runners. So I took this into thought knowing it would be a waste of time.

    What do you mean by aerodynamic? There's nothing in there that really splits flow. If you mean what I think you do which is put a taper into the entry way of the port that wouldn't help. Only on an intake with an actual runner would it help. You make a taper to the port from the runner on the intake to follow the runner shape on the port. I experimented with it by tapering the port itself and actually lost velocity and CFM stayed the same. However, if there was an intake such as a single/dual plane, tunnel ram or individual runner then it would help alot.

    The SC intake is too bad of a design, no matter what you have modified it to you aren't going to get near what a runner type manifold will.

  8. #8
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    There is no reason one could to flow with the manifold bolted a head.
    And bolt a plate on the others side of the manifold.

    I would like to raise the floor and the top of a manifold. Raising
    the floor of are SC bird manifold. I think would be a big plus on
    the entry of air to the intake ports.

    By raising the top and bottom we can keep the important plenum
    volum, since this is a blower motor.

    Randy

  9. #9
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    When flowing to try and simulate all of that, can you also get the flow bench to bring the pressure up above atmospheric by any amount of boost?

    It would be interesting to know. I.e., back cylinders ( or any other cylinder, this is just theory) gain an unproportional flow, but boost causes them to hit their max, but luck has it that their max is met fast, air flows over into the next set, and that's met fast, and the air flows into the last one really fast as well. I.e.,due to the excess pressure all cylinders reach their fill by the time the valves close.

    Thus it would be interestig to know.

  10. #10
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    There is no way to get true numbers with flow tests of any type.
    Be it on a air flow bench to measure CFMs ,air speed, air direction,
    with the use of air,or air with dies,smoke as a marker for measurement.
    To use as a judgement tool.

    I have read about a flow bench being built buy a shop owner to flow
    test A complete long block. Less crank, rods, pistons.With the block
    having the bottom of block cut off .From the bottom of the cylinders
    to oil pan rail.And make claims that this is the closest one could get
    to real world flow numbers.The guy used a degree wheel on the cam
    and to turn the valvetrain,& Dial indicator to read valve lift.

    Air speed measurement was mentioned. I believe the name for the
    tool to read air speed is a manometer.It is basicaly a fan blades with speedometer held or placed in the airs path.You can purchase hand
    held meters or mount to flowbench.

    It was mentioned about tapers in manifold and runners.If you cut a
    SC Bird manifold in half. You can see the manifold tapers down toward
    the intake port entrance. I think this not to be to bad of shape for
    an open blower manifold ,that fits under the hood. I think we would
    have a jump in air flow performance. If we could flip the manifold over
    And raise the heads intake ports floors runners.

    It would be to much work to mod a stock manifold. But it would be
    nice to try and cut out the top and bottom of are manifold out.
    Flip the peice over and weld back in. This would help with air flow,
    by raising it up to go down into the intake port.Instead of the almost
    S curve the stock air path has to travel. And the manifold would still
    be tapered toward the intake port to increase air speed with volume.

    This post is making me to want to be able to go to the shop and work.
    And kick myself for selling my flow bench a few years ago.But it was
    small,old,and collecting dust.

    Randy
    Last edited by Randy N Connie; 07-10-2006 at 08:26 AM.

  11. #11
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    Yes I understand that it would be too much work. I was just saying that it isn't near an optimal intake. Ford just made a design that made everything fit and that's the most you can say about it.

    There's a small taper in the port, but an effective taper is in an intake runner that, i've seen, atleast has 6"-9" long. The taper increases velocity a big amount.

    The reason for raising the port is to get as much as a direct shot, or straight line , of air into the port as possible. The reason why every head i've ever worked on (with exception to casted Pro Stock heads) the ports have be raised significantly.

    Always remember this. First comes velocity then flow. If you get alot of flow, but velocity is killed then it hurts motors quite a bit. You have to work with the head to where you can match a good velocity point to CFM then keep going on flow until the velocity numbers start falling. Then you go back to where it was.

  12. #12
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    I was wondering. Since our motors only make power under boost, is it better to flow the intake ports draw through or blow through? I know exhaust ports are flowed blow through because that is how they work - well, aren't our intake ports working the same way under boost? The cylinders do not draw air in, it is pushed in.
    Quote Originally Posted by Miller View Post
    Ya thats why i tape mine down. People think its bc i dont have a moonroof seal (which is true) but its really to keep my roof from ripping off .
    Email me here.

  13. #13
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    The closer you can simulate a test to the real world. I would think you
    would receive better data to judge with.

    With the manifold being open & working as a plenum. I would
    think flow test results would be different & better buy pressureizing
    the manifold with blow though air.

    There are many different types of flow tests that can be performed..

    I have heard that some old gear heads ,would use superchargers
    when building there flow bench.

    Would,nt it be nice if we could just gut the motor of piston crank rods,
    remove oil pan. then Bolt the block down on a big home made flow bench table. And drive the blower with an electric motor. If thats what you want,
    I think it could be built easy. All the parts are for sale.Just need to be a cabnet builder to hold it together.Or Superflow would build one for ya.

    I bet some one like John Force's shop has a bench set up to do this
    type flow testing. pressure blow though.They machine there own
    blower rotors in house,and use a blower dyno for testing.It would be
    nice to see how they do air testing on the blower, intake, heads, block,
    as a system.

    Randy
    Last edited by Randy N Connie; 07-10-2006 at 02:57 PM.

  14. #14
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    Setting up a blow through system isn't in the cards for me right now because I don't have time. Sounds like a winter project....

    Anyway, I have concluded that the stock intake manifold will cost you about 8-10 cfm on a stock intake port and simply opening the manifold to match doesn't help. You have to put some thought into it and contour the port inlet on the manifold to get back your 10 cfm. I think port entry is critical even on a box intake like ours. This is something that Trick flow did on their new blower manifold. Unfortunately we can't duplicate that kind of port entry but from what I've seen if you don't at least try you will be leaving flow on the table.

    So my next question, is what port diameter is necessary to support say, 250cfm if velocity is good?
    Quote Originally Posted by Miller View Post
    Ya thats why i tape mine down. People think its bc i dont have a moonroof seal (which is true) but its really to keep my roof from ripping off .
    Email me here.

  15. #15
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    The SC head that I got 260 out of I had a 1.6"x1.31" port. I could have gotten more, but there isn't enough meat to raise the port.

    As for blow through testing, yes it is more efficient to find velocity points. We had a new machine that showed in the computer where the air speed was slowing down. Fill that in or take it out where it says and leave it. It works well.

    You still can't use it to predict CFM though, only velocity. Draw through CFM is a direct correlation between forced induction and natural aspiration. The difference is in velocity.

    Forced induction LOVES square intake port designs.

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