Jerry Feather

When they "deemed" it sufficient I wonder what other configurations they were considering. This one isn't mounted at the center of the plenum and it isn't even mounted straight, yet it appears to work; so I might conclude that one or two inlets and where they are located really doesn't matter much.

ptuomov

Why would the plenum volume make any difference with eight cylinders feeding from the plenum? What's the logic?

Jerry Feather

You posted your opinion about this twice. I didn't respond to it the first time because I have no basis to suggest otherwise. Your posting it twice looks to me like you are just fishing for something to argue about; and your current post seems to confirm that. I don't have any basis to argue about it one way or the other. Perhaps Carl might have some knowledge about it rather than just an "opinion," but if he comes up at all about it it wont be until next week.

ptuomov

Thats my opinion. It's got some basis on fact. The 1D simulator says there's very little sensitivity. Also, the passenger side spacers on the S4 manifold make some difference when flappy is closed but empirically none when the flappy is open. I've never heard a credible and/or logical argument why the plenum volume of 8-cylinder single-plenum port-injected manifold would matter beyond making equal distribution easier or harder. But if someone has one, I'd love to be educated.

Jerry Feather

Now you have said it three and maybe four times. From my perspective it is a Who-GAS. I still don't have any basis to argue about it; but it's nice that you seem to have found an opportunity to state your side of an argument that doesn't seem to exist.

Jerry Feather

Did some patterning for the last piece of the plenum, the little piece for the other side of the front. Then I took my measurements and roughly cut out the plate for the top of the plenum. I have approximated the hole spacing for the top plate and will finalize that layout, then when I decicde on just what and how I will put some support posts inside the plenum to keep it from flexing up and down with the vacuum pressure, I'll start milling the fins on top.

Jerry Feather

I haven't yet decided just how to mill the grooves or fins into the top plenum plate. The choices I seem to have are to make them longways, crossways, or parallel to one or the other of the two front angles.

I made these finned aluminum items some time ago for my spare airplane engine that I was planning to install in my Navion. Like many of my projects it seemed to get too complicated to finish. Anyway, something like this is what I kind of have in mind for this plenum top plate.

Here, on the airplane engine, I have both the straight forward fins that I made with these finned aluminum rocker covers, and I have the angle grooves in the quarter inch plate that I made for the sides of a new design of cooling air box for the top of the engine. I kind of like the angle grooves; and I think I am leaning to doing my plenum plate grooves at an angle, probably the sharper shorter angle from in front.

GregBBRD

Jerry:

You have good fabrication skills. Looks great!

Jerry Feather

The Subaru setup looks virtually identical to the configuration of the 928 intake. My plan is to stay very close to the 928 design although I'll have to figure out how to make it somewhat lower in profile. One thought is that I may actually end up more like the Subaru design with the air filters somewhere else than in the airbox just ahead of the TB.

Jerry Feather

Thanks, Greg.

Most of it stems from an early realization that if you need or want something, you might be able to just make it for yourself rather than having to look for and buy it. The other part of it is the trick of having the tools and equipment, or ready access to them, to do any of the fabrication tasks needed. With all of that I have taught myself to work in several different mediums and with many kinds of materials. Beyond that the limit is only in my imagination. I have found that if I can conceive of something I can probably make it. The limitation is in my ability to conceive of something; and that relates to some areas, particularly in the field of electricity or electronics.

Jerry Feather

I did some machine work on the top plate including truing up the edges then rounding them at a 3/8 inch radius with a corner rounding mill bit. The rounding I think softens the otherwise kind of "heavy plate" look it has with square edges. Then I drilled and recessed all of the screw holes.

I have ordered some socket head screws and some nut plates to mount the plate with. Now that I have the plate cut to size I can do the final fitting of all the pieces and then begin to weld or get it welded together.

I have also cut some sample grooves/fins in a piece of the plate scrap with a small taper mill bit just to see how wide they might want to be. At .400 in. spacing they come out so that the top of the groove is about .290 and the top of the fin is .110. That's pretty close to what I want, but now I have to see if I can get them spaced correctly in the top plate. I don't want the fins to be much or any narrower, but I might go to a slightly small taper bit for the grooves.

The three holes in the middle of the top plate are for three posts that will connect the top plate to the bottom of the plenum.

ptuomov

Fantastic fabrication work! By the way, I didn't want to pollute your thread with plenum size arguments. Sorry about that. On the plenum construction, Todd Tremel I think has some experience in not only making an intake for 928 but also constructing real pressure vessels. You could ask him for informed opinions on the plenum construction.

Jerry Feather

Thanks P-2. If there were an argument about plenum volume, this might be the right place for it, except that I have pretty much locked myself into this size every early on with all the compromises I had to make in meeting my design goal - - lower profile. Is Todd Tremel on here? Likewise, though, I am pretty well stuck with what you see here. The only thing I might do different is anything, but only if this one doesn't work almost at all, and I don't see that happening.

For Carl's inquiry about the plenum volume, I forgot to deduct the volume of the MAF tunnel in the rear bottom, but I haven't calculated that yet. I think it might be only about 10 or 12 cubic inches. The same for the little one in front, but only about 3 or 4 cubic inches. Then, I found online something that suggests that the volume inside the tubes is also part of the plenum volume. There again, all of this is purely academic at this point.

Tom in Austin

Cool stuff, my favorite Rennlist thread right now!

Jerry Feather

Interesting, Tom.

I couldn't wait any longer to try to cut the grooves/fins in the top plate, so I laid out the outlines to mill up to and set it up in the mill. I made real good progress until I got about halfway and had to move it on the mill table, but after I got it moved I didn't clamp it down well enough and had my clamps kind of off to one end leaving too much leverage for the mill bit to push it out of alignment.

Here are some pictures of my progress then of my failure. The only upside to this is that I still have some material to work with to start over, and I can take an opportunity to give any reconsideration to my design and maybe even the layout of the mounting screws, perhaps so that they come out more like they relate better to the grooves. That may be too hard to lay out for what little that might matter.

Aside from reconsidering my design I at least can simply duplicate what I have done to this point without going through all the planning and figuring that I did to get this far on the plate.