EvanSG

It is wonderful that Jerry is undertaking this project. I've been frustrated for years with the lack of new intake tubes for my 86.5. Sign me up!

I would be okay with having to remove the cross brace to install/remove the tubes if it meant that the tubes are more robust than the OEM tubes (less likely to crack) or have the largest possible diameter at the restriction point.

EvanSG

Someone earlier in the thread, I think, proposed making the tubes in two halves that are later glued together, so the halves could be removed from the moulds more easily. In that case, would the halves be made by having both a positive and a negative mould that are pressed together around a (hot) sheet of ABS? I realize this would imprint any small imperfections from both moulds, but would that really be so bad?

Jerry Feather

Hi Evan. This idea raises some interesting thoughts, but the main one is that I don't think I am capable of making the mating molds, male and female, with the degree of accuracy that would be needed. And, there would have to be four sets of them.

Keep thinking about it though because that is how things get created.

EvanSG

Can't resist thinking a bit more about this. Let's say you first make just two male forms: one for the left tube, one for the right tube. Then the female forms could maybe be made using something analogous to the lost-wax process (http://en.wikipedia.org/wiki/Lost-wax_casting). Finally, you would cut the forms in half, ending up with four sets of male/female.

Jerry Feather

Good, Evan. Keep thinking! And, while you do think about how you are going to account for the thickness of the material in between the two forms/molds that the final product will be made of; and particularly the thickness it will end up being after it is stretched out from its original thickness to its final thickness, and as it might vary in thickness at various points.

Then think a little more about just what it is that is analogous to the lost wax casting wax process that you have in mind. I have done some of that in the past and know a bit about it.

EvanSG

Maybe the thickness could be accounted for by laying up some material on the male mould before casting the female mould. E.g., fiberglass strips or something. Similar to how carbon fiber is laid up with multiple layers of strips. I understand that would leave stripes on the female mould, but it doesn't really matter how smooth the outside of the final tubes is, right?

Another idea would be to mold ABS by hand around the male form (heating and shaping a little at a time), then cast the female form around that. That might help to account for varying thicknesses of the ABS at different places.

The lost-wax idea was just to create a female in something like plaster, then "convert" the plaster into some other more durable material in a similar way to how clay or plaster sculptures are "converted" into bronze. Anyway, I'm just talking out of my *** here, because you obviously know a lot more about all this stuff.

Jerry Feather

If the male forms were made out of something hard, like oak or such, then what do you think of the idea of using something softer than bronze or epoxy or whatever, more like air, for the female part of the process to force the plastic onto and into the shape of the male forms?

EvanSG

Okay, fine. They were just random ideas. Carry on.

Jerry Feather

Darn, Evan. You sound like you feel like I am putting you down in some way. Actually I am really enjoying helping you in what I think is your thought process, and in so doing trying to help you understand that this is just how my mind works, and perhaps how I have already done this in my own mind and how I have come to the point in this project that I have come to.

You sound like you have given up in the process, and I think that is too bad. I think your thoughts about this are much the same as mine and it would be worth your while to continue the process, even though you may be able to tell now where it is leading.

EvanSG

Well, okay, I'll pursue this a bit more. So you then think about blowing the ABS onto the male form, and then realize that vacuuming it onto the male form is easier and better, etc., and you end up where you are now, which is probably the best way to do this.

But let me play devil's advocate for a moment, and argue for using hard male and female forms pressed together. I can think of some advantages to the male/female forms. Since the male/female forms are halves, not the whole tube, you don't have to worry about: (1) making your male form out of several separate pieces so they can be removed, (2) gluing the cylinder of ABS before forming, (3) making a vacuum-tight seal at the ends of the cylinder, (4) getting the diameter of the cylinder before shrinkage just right. Furthermore, it would probably be easier to get the left or right bend in the half forms, instead of heating up and bending after the fact.

Anyway, I appreciate you encouraging me to think about this stuff. It's fun to armchair quarterback.

waynestrutt

Evan
Only one form or mold is required to make both sides.They can be joined with abs cement . A flange would make joining easier but is unsightly unless done with very small hex socket capscrews. Aside from absorbing vibration and maybe allowing ease of installation, I cannot see the need for the corrugation. a 3" rubber plumbing coupling at both ends will accomplish that. The venturi design accelerates the air flow and lowers the temperature of the incoming air so should be incorporated.

Jerry Feather

Wayne, for the 85/86 version of these tubes, "Only one form or mold is required to make both sides" is not correct. The is, unless you would intend to modify the finished formed version of the tubes with heat and something else to put the definite kink in them that is required.

Wayne, how would you intend to glue two halves of these form components together with ABS cement without having flanges along the joined edges?

Wayne, your thought about leaving the corrugations out may have some merit, but I think they may be necessary at least because of the movement of the motor in relation to the engine bay, and probably for other reasons.

Wayne, the sort of venture design probably does neither of the things you suggest. The air may accelerate at the tight point, but then it slows down as the tube opens back up. To the extent of any very small change in the air temperature relating to the tight spot, I think it is just the opposite--the faster air will likely be hotter, and that too will revert as the opening gets larger. I think the sort of venture is actually a reverse megaphone designed to somehow reduce noise coming back up the intake system from the engine.

Evan, There is probably a number of methods to form plastic sheet to the contours of a male form while using heat to make the plastic more formable. Yours, with the nearly exact opposite female form is probably the most complicated one of them. Although it might very well be the least complicated in production, it certainly will be the most difficult to fabricate.

Another thought might be to use something like rubber and some kind of pressure to get it to force the plastic around the male form; and possibly rubber and some hydraulic force. Botyh of those are used in forming sheet metal over a form.

Moving up the element stream, so to say, we find ourselves where I am--using air to do the forming for us. We can use some kind of pressure chamber and blow air into it to force the heated plastic over the form, or we can use ambient air pressure, like I am going to use, and just remove the air pressure from one side of the plastic so that ambient air pressure will force the plastic onto the form. The first of these is pressure forming and the latter is vacuum forming of vacu-forming. In both of these cases we only need the male form letting air take the place of the female form.

Jerry Feather

Evan, more specific, to you four points above; as to (1), it will be almost as easy if not easier to turn two separate but matching male forms in the lathe using two pieces of wood for each rather than the 9 that I have used, and then forming the kink in them after they are turned, separating them in halves and laying them out on the vacuum table for forming.

As to (2) you are right about the tube gluing. That issue gets shifted to a later point in the process where we would be trying to join the formed halves.

About (3), the vacuum tight seal, is not actually air tight but just very air restrictive. All that is needed is enough of a "seal" so that there can be created a pressure differential for a few seconds.

Then (4) that is not an issue or it is the same in any given process. The male form needs to be the correct size however it is made.

Now, more about the what I see as the real problem with your process, and that is joining the two halves together after they are formed. In this regard let me suggest that there are about four categories of design criteria. One is fit, one is air flow, one is noise control, and one is finish or appearance. For me the latter is the most important, the noise aspect is of least importance and the other two are in the middle, about equal in importance.

So, since the gluing of the two halves will likely have to be on the outside (or maybe not??) they play a big part in appearance and likely in fit. Is there room for flanges? What will they look like in the finished product? The reason I say maybe not is that I had a thought about forming these tube halves in the Vacu-forming process in such a way that one of the mating edges could actually be formed inward in which case it could be joined inside the tube. The other flange edge will still have to be formed outside in order to get the plastic off the forms when it cools. That may help some in the appearance; and then we would have to decide whether to put it on the inboard or outboard side of the tube. It will probably look better on the outside, but on the other hand, it may have to be on the inboard side in order for the tubes to fit the narrow channel provided in these 85-86 cars.

Then, you and Wayne may have a better method of gluing these halves together that has not occurred to me. Let's see what Wayne has in mind.

EvanSG

I think you may have missed my point on (4), or perhaps I missed your point. My point was, if you glue together a cylinder of ABS before molding, it has to be approximately the right diameter so that it fits snugly to the male form after it's heated and shrunk. Also, if it's the right diameter in some places, it's going to be slightly the wrong diameter in others, because of the tapering male form. I can see how this might not be a big deal if it's okay for the ABS to shrink quite a bit more in some places than others.

In my male/female half form idea, since the ABS is not glued in advance, you can just use a bigger sheet than you actually need, then cut off the excess after pressing the two forms together.

I agree with your point that my male/female half molds, while perhaps easier to use in production, are harder to fabricate. It's just a thought experiment. I'm sure you'll get your vacuum-forming idea to work.

Regarding the flange: I don't think the outward-oriented flange would look that bad. Perhaps in the most restricted area where it bends around the corner of the intake plenum the flange could be inward.

Regarding Wayne's idea of removing the accordion folds: I wonder if both functions of the folds, namely ease of installation/removal and allowing for the engine movement with respect to the frame, could be accommodated instead with a sufficiently large rubber coupling. Some calculations are in order here to verify this hunch.

SMTCapeCod

With respect to the folds, IIRC, without the folds one would just have to remove the screw/bolt in each snout/intake at the radiator, and give it a nudge forward. And maybe pop the strut brace for additional convenience. Unless the clearance that affords is inadequate.