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I'm porting my stock GSR intake manifold.

Discussion in 'Engine Building' started by civicious, Jun 28, 2005.

  1. civicious

    civicious FüK-VTEC VIP

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    So I scored a spare GSR intake manifold for damn near nothing a few weeks ago, and I'm finally getting around to porting it. I'm going for something like the DH racing manifold:
    [​IMG]

    Only thing I'm going to do different is make the dividers a little lower, maybe a half-inch or so...I was also thinking about maybe staggering them so that the one closest to the TB is shorter/lower, and they rise up by a millimeter or 2 as they go away from the TB...

    The red is a general outline of what I'm taking out...not exact, but close.
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    Thanks to ImageShack for Free Image Hosting


    Also, I know Erick Aguilar used 2 spacer thingies on his manifold...anyone have any idea why? Obviously it works, seeing as he ran 9's on a more or less stock GSR manifold....but what's the science behind it?
    [​IMG]

    Comments? Please don't give me any 'Just buy a skunk2 manifold' bullshit. I'm not losing any money, and I want to see how much power can be made with a stocker.



    Comments? Suggestions?
     
  2. formby

    formby learning in progress

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    my boy did the same thing...but he removed the entire dividers.....and polished the entire inside part...ohhh so smooth
     
  3. PhyRe

    PhyRe Senior Member

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    yeah i always thought you would want the runers themselves to be ported not between the pieces.
     
  4. formby

    formby learning in progress

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    ported is not the same as polished
     
  5. n1mr0d

    n1mr0d Senior Member

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    I am not going to tell you right or wrong or what to do. I am merely going to state what works in the physical universe.

    1.) Velocity>flow. The faster the velocity into the cylinder the more air that will cram into the space for combustion.

    2.) The intake runners should be in a smooth conical shape tapering down to the intake running.

    3.) Polishing the intake will do nothing for you except waste time and money. Especally at this point of the intake because fuel has not even been injected into the air stream yet. Even after the point at which fuel is injected, a rough surface is better to keep the fuel in suspension longer.
     
  6. civicious

    civicious FüK-VTEC VIP

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    I'm...um...not polishing it...i'm taking out all that extra dual-stage bullshit...
     
  7. MikeBergy

    MikeBergy Blah blah blah....

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    1.) This is not always true. Like at the top end of your power band. You'll want both. You don't want to bottleneck your top end for the sake of low end response. But it depends on what you are building for.

    2.)What you said makes no sense really grammatically, but I kind of almost agree with what I think you are thinking. You are trying to generalize a way to increase the velocity in the runners, but you forget as the velocity and therefore dynamic velocity increases, your static pressure is going down the tube, and you have to find a compromise somewhere that satisfies your power goals. The dual stage runners are there for a purpose, and they do a good job for the most part.

    3.) Polishing is not a waste of time and money otherwise people wouldn't do it. It cuts down on pressure recovery losses in the plenum an runners, annd ultimately comes down to greater engine efficiency. Now, it has more to do with the actually design of the IM than the wall finish, but it still offers gains, and if you are a DIY'er, all it costs you is time, for research and the actual work. Just make sure to rough up the last bit of the IM before the flange, to induce a little turbulence. You definitely don't want fuel pooling up on the walls.

    Will... I don't know if I would cut out the entire dual stage IAB's unless you are just working to increase the top end. The gsr is known for its midrange power, mostly due to that dual stage intake. I'd just open up the holes a bit more, and leave the dual stage in if I were you. Since you got it for next to nothing, you could test different stages of IM porting, opening the holes up bit by bit, testing it as you go, and see what happens each time you modify it. That would be a fun way to learn about what works and what doesn't. As for Aguilar's setup, I would imagine that the spacers are more or less tuning the length of the runners for his setup. They also allow a bit more volume after the TB, allowing a larger column of air to be crammed into the port, it seemed to be a mass-momentum-total pressure thing to me, but that's only a guess.
     
  8. n1mr0d

    n1mr0d Senior Member

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    1.) Yes velicoty and flow are both wanted at ALL rpm ranges. So the opening at the choke point (which will be the true bottleneck because it should be the smallest) needes to be a size that will allow enough air pass so that it not choke the engine.

    2.) Perhaps I should have worded it as "The intake runners should be in a conical shape tapering down to the intake port."
    Please explain the principles of the static pressure and what it is needed/used for?

    3.) Please explain the theory of pressure recovery loss.
     
  9. sihatchback_RL

    sihatchback_RL Senior Member

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    CHP has done this back a while ago, Loses BIG TIME low end power, didn't pick up till 7000 in a built GSR running 14.2 compression. dynoed at 203 horse, then slapped on stock gsr, ran 254 horse, BIG DIFFERENCE!
     
  10. MikeBergy

    MikeBergy Blah blah blah....

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    I don't understandd exactly what you are saying. Are you sayng that they tried out the hogged out IM, then slapped on a stock gsr IM and gained 50 hp?
     
  11. 92civicb18b1

    92civicb18b1 The Trisexual

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    i assume it could be true but I doubt it.

    I say go for it.
     
  12. MikeBergy

    MikeBergy Blah blah blah....

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    1) Correct. unfortunately youy have to build and tune the engine for an optimum design point, and that is going to determine how big you make the ports, shape, length etc.

    2) Static pressure is basically the manifold pressure, or pressure not affected by flow velocity. For an N/A application, it is near the ambient air conditions, that is, close to 14.67 psi, or 1 atm. But, you can pressurize moving air by slowing it down gradually, and this is what intake plenums are designed to do. It isn't a lot of pressure, but any pressurization is going to allow more air to be crammed into the engine ata given time. more air = more power potential. so you design the IM to gradually slow the air down to gain static pressure. On the other hand, you want dynamic pressure as well, because that is what allow the cylinders to continue filling after the cylinder reaches BDC. So you basically want both, but where you choose to optimize your powerband will affect the balance of static and dynamic pressure.

    3) Static + Dynamic = Total Pressure. Pressure recovery is just a measure of efficiency of the component the air mass is flowing through, in this case, the IM. Say you measure the total pressure at the entrance and exit of the IM, you are going to have less total pressure at the exit due to flow disruptions, poorly designed turning in the flow, etc. Pressure Recovery just = Total Exit Pressure/ Total Entrance Pressure. Smoothing the walls through most of the manifold will cut down skin friction drag in the manifold, increasing the overall efficiency of the mmanfold. But like was mentioned before, turbulence is a good thing near and in the port, because it helps to further atomize the fuel-air mixture, whichis good for other obvious reasons. But polishing the manifold will allow the total pressure entering the port to be higher. Now, this isn't saying you'll gain 2342374234 hp by doing it, but if you were racing professionally, every extra .5 hp gain is worth the extra work that goes intoo the manifoold design/modification. For Will's case, it probably isn't, unless he want to spent the extra 15 or so hours it would probably take to properly polish it. It's not practical to do it for a street driven car, and most people don't want to pay extra to have a machine shop do it. But it isn't a waste of time. It's cool that you ask questions, show that you actually are interested in how things work, and not just interested in the end result, namely going fast. I am inspired constantly with new things to try on my car, but until I have the money, a lot of those experiments won't happen. I just research the material in the meantime. Good luck with the project will, and document your progress, so we can hear about it later. :)
     
  13. n1mr0d

    n1mr0d Senior Member

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    I can see how this would happen because the incoming air is coming from a smaller inlet (the throttle body) to a large open space slowing the incoming charge down then asking it to speed up again to get into the intake port/cylinder. It's extremely inefficent.
     
  14. MikeBergy

    MikeBergy Blah blah blah....

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    Yes and No, I'll be back to comment later, I gotta go back to jury duty :(
     
  15. n1mr0d

    n1mr0d Senior Member

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    I can understand why you would want to slow the incoming charge down in order to better fill the cylinder? Why wouldn't you want the incoming mixture to continue flowing as fast as possible increasing its velocity? It seems counter productive to slow the mixture down to increase the pressure because the end result is power not pressure. You need to speed it up (velocity) to create more power.

    Yeah and ask more questions!
     
  16. MikeBergy

    MikeBergy Blah blah blah....

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    Did you mean can't ? You don't want to slow the flow down to where it can reverse, but you do want to slow it down. Here is an analogy. Traffic accident on the highway. All the cars start to slow down, and the flow of cars through a spot near the accident becomes more dense. That is the best analogy I can come up with. I'll never be a teacher :) . As the air is slowed down, the air molecules are forced closer together by collision with decelerating molecules in front of them. You want the flow to be as steady as possible going into the head, meaning no flow reversion. That is where velocity comes into play, because you want the air to have enough momentum to continue to fill the cylinders, but not to the point of where the velocity is so high that it drops the pressure to below ambient. You don't want that because density varies directly with pressure (perfect gas law), and the lower the density, the less power you make. Velocity in this case is not the only thing that affects power, but it is a factor. Anyway, I'll stop cluttering up this thread... :)
     
  17. civicious

    civicious FüK-VTEC VIP

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    Uh...yeah...so...um...


    So I'm gonna take me a die grinder and waller out that there intake manifold.


    Mm-hmm.
     
  18. MikeBergy

    MikeBergy Blah blah blah....

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    :mullet:
     
  19. phunky.buddha

    phunky.buddha Admin with a big stick Admin VIP

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  20. HatchSpeeD

    HatchSpeeD ...Hi...

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    So thats why ITB's are so effective. Good information. :thumbsup:
     
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