dr bob

Jerry--

Glad to hear you are recovering from the knife and saw.

Keeping in mind that the plenum will see about 15 PSI of external pressure under trailing throttle, have you considered stiffening ribs in the larger sections? These could be rolled in pretty easily. If the bends are made on a press brake, it's similarly easy to to strengthen them with some formed-in ribs to stiffen the corners.

Jerry Feather

Excellent thoughts, Dr Bob. I have thought about it a bit but did not come up the any need. Here are the reasons:

1. The bottom will be screwed the the TB plate which is 7 inches wide front to back. In back of it there is going to be a rounded tunnel for MAF clearance under it. In front it will extend about 5 inches forward to where the front sides begins.

2. The left and right sides will consist of the same sheet material that is bent longways at a 90 degree angle and the widest part of either of its flats will be only about 4 inches. The bottom flats of each side will have the 4 holes through them with the tubes welded to them. The upper flats going from the 90 degree angle over the the top flat flange will be the largest plain flat surfaces on the plenum. Given that they are going to be pretty narrow I don't think they will need stiffeners.

3. The front and back will each consist of 6 facets plus the flat flange along their tops for the top to mate to; and the back will also be intersected by the curved MAF tunnel. I'm pretty sure that none of the facets will need to have a stiffener on it.

4. The top will be made of a 3/8 inch aluminum plate that is machined to lighten it and to make it look like something resulting in ribs longways that are about 1/4 inch deep. I think that will be pretty stiff in itself.

Jerry Feather

Hi Dr Bob. I have given your concern some more thought and have kind of done some rough math associated with it. The math suggests that with a vacuum created inside the plenum the atmospheric pressure on just the top side of this thing will be upwards to 2700 pounds. When I run that through my mental pressure chamber I can envision this plenum looking much like an empty beer can laying on its side on the ground and being stomped on. Therefore I am deciding to put what I will call some pressure posts inside the plenum between the top rim and the bottom surface. There will be at least four of them and probably 6 if I can find the right locations for them so that they are screwed in place at least at the top with the series of socket head screws holding the top plate on.

On another note, I find that the guy who bent the plenum floor for me has missed my 60 degree angle by about 3 or 4 degrees. I'm going to have him adjust those bends and then have him put the bends in the two sides of the plenum. If I find the strength to go out to the shop later I'll cut the sides out and mark them for bending.

Then, depending on how I feel I'm going to devise the pattern holes for locating the openings in the plenum sides for the tubes to pass through and then I can start working on that pattern. It all depends on how much time I can spend on my feet.

dr bob

Glad the discomfort from the back work hasn't dampened your spirit of progress and development. However (sounds so much more pleasant than "but"), I and others (like your surgeon) will warn you about overextending yourself during your early recovery period. Pain meds can easily make you think you are in better shape than your body would otherwise signal. Pay careful attention to the recovery guidance from the MD's, and the signals you receive when you are moving around. Needless to say, you don't want to go back for rework if it can be avoided.

M. Requin

Recovery guidance from MD's is important, but they often overlook the importance of a good PT in the rehab process. I found one who was a sports medicine type, and had actually been to the OR several times to observe back surgeries. My recovery was completely successful (admittedly a less severe issue than yours) and I am sure I owe much of that to the PT's regimen. I still do the exercises 2 dozen years later. And it makes sitting in my 928 an even greater pleasure (obligatory 928 content, don't want this to get like old men on a park bench etc etc). Very glad you are up and about and feeling good enough to return to work, as long as you heed Dr Bob's caveats (and those of others!).

Jerry Feather

Thanks Dr Bob and Martin. I had the surgery on Wednesday the first and it lasted from about 9am to about 3pm. Then I think I woke up about 3:30 or so. I didn't have a lot of pain and they had me rigged up to an IV drip which I thought was giving me some small dosage of pain med.
Then they explained that they also had it rigged up so that when I felt the need for more pain med I could push a button and get another dose and that it would reset itself when I was eligible to push it again. Thinking that at what was already in the the drip and that I could tolerate the level of pain I was having then I didn't push the button for about a day and a half. They were always surprised that I had not pushed the button and finally told me that pushing the button was the only pain med I was going to get that there was none otherwise in the IV drip. Then it occurred to me that they were not going to let me out of there until the pain was minimal, so I started pushing the button. I was there over three nights.

They gave me a prescription for a heavy narcotic and I got it filled, but I am relying mostly on Aleve (Naproxen sodium) for pain relief, and not much of that. I'm going to have a lot of dope left over for the next party we have.

Yesterday I finally made it out to the shop but only briefly. I cut out the two sides of the plenum and brought them in and marked them for bending. I think I"ll take them to town this morning and see if I can get them bent. I received a large tablet of graph paper so I can sit here and work on the drawings for the front and back of the plenum. I can see them in my mind but it is real difficult to put all the bends and facets on paper in three view.

I asked again about PT for my back and they were a little more positive this time, but sounds like it will be more after the fusions have solidified. I have a good one in mind, so maybe I can get a prescription for him when the time comes. The Surgeon did say that he is going to have me walking a mile a day after surgery, but that is not going to start very soon since I can't be on my feet for very long yet.

I saw my local regular doctor last week and he thought there might be some infection in my incision, but he cultured it and it turned up negative. He took me off the antibiotic he had prescribed.

Jerry Feather

I'm not spending much time on my feet yet, but I have been able to put in spurts of effort here and there. I had cut and marked the sides of the plenum and taken them to be bent. I picked them up yesterday and then found that I had made a small mistake in them. I was able to correct it by simply cutting the mistake off. I took what I have so far out to the shop and kind of mocked it up a bit to see where I am with it I found that I think I need to remake the plenum base a little bit narrower, but I don't think that will require me to change the sides. I'm going to draw it up narrower and check the fit with my patterns.

Here are some pictures of what I have going now, including a picture of how I am going to pattern the holes in the sides of the plenum for the tubes to pass through. I think these pictures will give you a better idea of the general shape of the plenum, although the bottom and sides are about a couple of inches longer that they are going to end up. As mentioned before, the top will be a heavier aluminum plate machined to fit and look cool. The front and back of the plenum will be pretty complex and it is still pretty hard to put into a drawing.

Jerry Feather

When I temporarily clamp these three pieces of the plenum together I find that the the whole thing is too wide at the base. When I put one of the tube hole patterns onto one of the tubes and put it into position it pushes the plenum base too far against the tubes on the other side. Therefore I have cut and marked a new piece of material for the narrower base and hope to get it bent early this week. Then I can start marking, cutting and bending the ends of the base and making provision for the two elliptical intake holes in it.

Based on my drawings I have also allowed about a quarter inch of extra material along the bottom edges of the two sides just to have a little bit of fudge factor. That is in addition to the ability to move the sides fore and aft about 3 inches which also gives me height flexibility since they are tapered. I think overall the pieces as they are currently designed will fit well within the height restrictions I have set for myself.

I can't do too much else until I get the new base bent, except work on elongating the tube holes in the hole pattern pieces I have partially devised,

Jerry Feather

I got the new narrower base for the plenum bent last week and put it kind of into place and started working on patterning the location of holes through the plenum sides for the tubes. I cut some pieces of scrap aluminum sheet and put holes through them to use as patterning pieces and have clamped a few of them in place. When I get them all in place I'll clamp the tops of them firmly together then try to figure out how to use it as a pattern to cut the tube holes in the plenum sides.

Jerry Feather

I put the rest of the pattern pieces on the intake and then sheared and folded some sheet metal to clamp them all too and did the clamping. This is real rough so far since some of the tubes are loose from their respective holes in the base flange.

I think next I will have the rest of the tubes welded up with their bell-mouths and then work them over a bit more to fit more snugly in the flanges then try the method of clamping them all together with their pattern pieces.

I expect this process is going to end up with about three different patterns before I finally cut the tube holes in the already formed plenum side pieces. And still I think the plenum side pieces are about a quarter inch taller than they will need to be.

Jerry Feather

Hans, I made this assembly/fabrication stand using the mounting bolt pattern off of one of my spare S4 intakes. I wonder how much difference, if any, there might end up being from using the matching bolt pattern off of the cylinder heads as mounted on an engine. Given some of the significant differences in port matching found in a factory engine, I would hate to find that my intake is an eighth of an inch off from matching the ports in the heads.

hans14914

Jerry. You will note that there is some play allowed in the mounting with the included bonded washers, but not a lot. I have seen some deviation between engines, so its a good idea to check before locking it down for good. I can give you the XY coordinates between the four corner bolts that I am using on my layouts if you want to compare.

Jerry Feather

Thanks, Hans. That would be great.

Jerry Feather

The kind of mock-up shown in the pictures above are just that. I have taken that all apart and am now starting to put it back together much more accurately. I think I am going to get the hole patterns on each side correctly lined up then locate the right angle top flange of the plenum in just the correct position so that I will know where to put the final holes from the pattern pieces. Then I think I have kind of devised a method to fly-cut the holes in the sides of the final plenum. I do't want to have to make them over since they are pretty well finished accurately except for the tiny bit of extra material I left along the bottom edges for a fudge factor.

Then I think I am going to have to take some time and finally teach myself how to run a decent bead with my tig welder in aluminum. I can weld with it, but my welds look terrible. The shop where I have always had such welding done for me is getting so expensive that I think this manifold will break me up before I get it finished up. The cost to finish up many of my projects is one of the main things that leaves me with so many unfinished.

M. Requin

Jerry, aren't you supposed to be taking it easy? Get a little total relaxation time in over the 4th at least, PLEASE!