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Thread: Throttle body - butterfly orientation

  1. #1
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    Throttle body - butterfly orientation

    Gents,

    Picked up a set of DC & O Components 45mm DCOE throttle bodies for the Gemini. Havent really worked out linkages and bellmouths and all that shit yet, wayyyy too early and wont really look at it till its on the engine and in the car. However, playing with them on the bench did notice something.



    Part throttle butterfly opening, say 25%



    View through injector area @ 25% throttle



    Is this right? The top tip of the butterfly moves FORWARD towards the engine, but at partial throttle it looks like it could be obstructing fuel/air mix? Almost looks like the injector would be squirting directly at the butterfly causing [in my uneducated mind] issues with drivability, fuel falling out of suspension etc. Should i be pulling these apart and changing the orientation so that the bottom tip of butterfly moves foward under throttle opening, that way not obstructing injector and allowing fuel mix to hang in inlet tract?

    N-

  2. #2
    Unregistered User Permit Roadsailing's Avatar
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    Quote Originally Posted by F3ARED View Post
    at partial throttle it looks like it could be obstructing fuel/air mix?
    that's how a throttle works

    don't have any hard data for you but turbulence can be a good thing as it can help with atomisation/etc.

    also most adapters to fit 20 valve 4AGE ITBs to 16 valve 4AGEs mount the throttles upside down for packaging reasons, doesn't seem to cause any issues that I have heard of.

  3. #3
    Non Compos Mentos Gammaboy's Avatar
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    I think it's actually better the way it is - the injector is spraying into an area of high velocity air at the tip of the butterfly - yes, it may partially wet out the butterfly, but it beats the shit out of spraying into the low velocity tumble that's coming down the back of the butterfly if it goes the other way.
    "Where can we get hold of a Vincent Black Shadow?" "Whats that?" "A fantastic bike," I said. "The new model is something like two thousand cubic inches, developing two hundred brake-horsepower at four thousand revolutions per minute on a magnesium frame with two styrofoam seats and a total curb weight of exactly two hundred pounds."

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    Wasnt sure so thought id ask, thanks for the clarification boys. Havent really looked that closely at injector locations on throttle bodies, usually the injector is well and truly south of the throttle blade. Just seemed....odd.

    Cheers

    N-

  5. #5
    Look behind you... Milkman Don's Avatar
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    Where did you find them? Looking at non sell a kidney (webber) options for the e21.
    Quote Originally Posted by Faux Forg View Post
    I agree with Rdyno

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    Ash, i found them second hand on a Facebook page. Took a bit of a leap of faith in posting money to an unknown person on FB, thankfully he turned out to be a decent bloke to deal with. In terms of cheap cheap options, can you do fab work? If you can get a triple weber manifold ive got a set of GTR throttle "plates" [ie no inj mount] that have the same centre to centre as a DCOE that you could be able to adapt onto it. Or check these out.

    http://racehead.com.au/products-page...basic-itb-set/

    http://racehead.com.au/products-page...0-itb-kit-e30/

  7. #7
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    That's actually a good thing-it's helpful in tuning, in my experience with ITB's.

    Most of the fuel the injector squirts in is NOT atomized, it ends up condensing on the port walls and the like. As mentioned above, the edge of the throttle will help pull some of that liquid fuel into vapor. The other helpful bit is something called the tau layer, this is the layer of liquid fuel that is condensed on the walls of the port and the throttle blade, keeping this layer a constant thickness seriously improves drivability. At low throttles, the throttle blade obstruction will help by keeping some fuel on the front side of the throttle, letting it bleed off and into the airstream into higher velocity areas, even though the volume of air through the port is low. If the throttle blade isn't there, *sometimes* you will see low-throttle tau layers being very inconsistent and difficult to tune for, due to low air volume allowing fuel to puddle and run down the port walls in waves instead of a steady stream. Those are the ports you sometime see a "wing" or ledge cast into to provide a low-pressure or pressure-shear area, to help whip some of that liquid tau layer up into the airstream. Other ports, (well designed ports, I imagine) no trickery is needed and you won't see much difference, no matter where the throttle blade is.

    That's my understanding of it. It's worked for me so far, but TK would probably be the brain I'd look for for better information on this. I think he had a big post here once on fuel shear and why he did the ports on something the way he did, maybe it was the big 308 thread?

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