Ok , say you're working on an old carb and you bugger up a throttle butterfly taking it apart. Or you've got this vintage Hilborn setup but it's missing a throttle plate. Or you decide to get creative and try and build an injection setup. You need a new butterfly! First things first a butterfly looks round but it isn't. it is actually oval. second the edge on a butterfly is not square ,it's bevelled at the leading and trailing edges and square perpendicular to the shaft. I needed to know how to make one and I did some reading. The Kinsler website has a wealth of info for anyone working on stack style injection. In their site they explain about their throttle plates and how they make them. They turn them on a lathe and use a 14 degree angle on the bevel. if you look carefully at the edge of this one you can see the bevel... The way to get the oval shape and bevel on a lathe is to make a jig. I used a piece of 2 inch stock and milled the end to 14 degrees. I then drilled and tapped two holes on 1 inch center in the middle of the top. I chucked the jig in the lathe and trued it up. I cut a piece of 060 aluminum slightly bigger than my butterfly and drilled two holes for the shaft screws at 1 inch center. I turned the piece and was shooting for .003 - .004 smaller than the bore I'm fitting it to. I checked the fit in the bore and it fits nice and tight with enough clearance to move. here is what I'm working on ......I want to call it "Hillbillyborn " injection ( no disrespect to Mr Hilborn)
That's pretty cool! I think technically, the shape would be called an "ellipse". By changing the angle, I guess you could machine a longer ellipse too that way for other purposes. Thanks, that's some great info!
Are the throttle shafts machined down a little more than halfway where the throttle blades sit on them? I was just trying to picture it and it seems like if you want to keep the throttle blades perfectly centered so they touch equally on both sides, that you'd have to machine the throttle shafts down halfway plus half the thickness of the blades too, so you have a little less than half the shaft remaining. Or do you slot the holes for adjustment and machine the shaft only halfway? Just curious. Thanks again. Looks like a real neat project.
I milled the shafts to half and adjusted the plates by using slightly bigger holes and some tweaking. I think the clearance makes up for some of the shaft offset also. I'm still trying to perfect the fit, I've made about 60 butterflies so far. Once everything fits together real nice I'll TIG it all together.
thats a neat way to do the butterflies, the thoughs i have had about making my own injection was to use a shaft for every butterfly and connect them like on a motor bike, then you can synchronize them with merc. sticks.
jethro, Looks sweet. Couple of observations if I may. You might want check the angle at which you are putting the injector. Theoretically you want the inector pointing directly at the intake valve. I would almost guess that with how you have them now the fuel will be bouncing off the wall and possibly back out the top of the stack.
The injector cup actually points down a little more but I hear what you're saying. I was going to angle them so they pointed straight at the intake valve but then I would have to plumb each individual injector rather than make rails. I've never done this before so it's all experimental( heavy on the Mental)I think I am going to use a Megasquirt system. Another reason I did it this way is I didn't want to cut up or weld to the Weber manifold that I'm using. I'll just be giggly like a school girl if it even works!
beats the hell out of getting junkyard butterflies that may or may not fit! I learned something new today, thanks!
Great looking Hilbillyborn injector. I am impressed. It should work real nice. I found that when we got into building injectors for the street the biggest problem was the butterflies sticking. I hope you dont mind if I share what we have found. With the butterflies being elliptical they will close and touch the wall well before they are parallel to the shaft. This allows us to control the air for idle speed yet when you start to lift the butterflies from the closed position you will have end clearance that increases all the way to WOT. If there is not enough end clearance the butterflies might stick. Another thing we have found is when the injector heat cycles aluminum will move around, which may not be as big a concern with your billet throats, so we have install couplers to allow a pair of butterflies to operate independently of the other pair which has totally removed the sticking associated with one single straight shaft. These couplers can be found at McMaster Carr. Lastly I would consider keeping the butterflies floating and not welded. You would be surprised how often you might have to adjust them <O Best of luck with your project it looks fantasic! <O
Sweeter than apple pie! Just one question. I noticed that you are using one long throttle shaft for each side. Since the manifold is aluminum and the rod is I'm guessing steel, they have very different rates of thermal expansion. Do you think it is possible that some of the butterflys could be pulled against the side of the throttle bore when the thing gets hot? Just a thought. I was thinking that the Hilborn setups use a slip joint in the middle, but maybe not. Maybe the clearance is enough for that to not be a problem.
Wow!...Thanks for the reply!....Sorry that I haven't responded sooner but I've been away for a couple of weeks. I've put some thought into what you have said and I'm going to split the shafts and use couplers to connect them. When I said I was going to TIG it all together I was talking about the throttle bodies to the base plate. I am using screws to attach the butterflies to the shaft. Thanks again for the expert advice!...I'm just " wingin it " right now surfing the web for articles and hoping experts like yourself chime in to give me some hints.
Hey Shiny! ....hoping to make it work first, probably use it on the 39 as a test bed, then who knows?
Oh, the angle. I wouldn't have even thought of that. Nice work! -- and thanks for showing us the details of it!
Nice job on the injector setup. Thanks for sharing what you are doing and teaching us a thing or two along the way. Joe
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