123quattro

Eventually you might want to think about doubling up on the thickness of the plenum. I don't think that would survive an intake backfire and will also flex a lot with load. Very cool project though.

Lizard928

What is the purpose for lowering the height on the intake further than it already is?

hacker-pschorr

...

Jerry Feather

I got off a little early this afternoon so I spent a little time with the intake. I made a pattern for the rear panel, adapted the rear tunnel and trimmed the rear ends of the sides.

It occurs to me that this project is a lot like putting together a large 3 dimensional puzzle, but one you have to make all the pieces for as you go.

I woke up the other night thinking that I might not like the fairly sharp corners on the rear as these are going to turn out and that I might want to kind of "dock" them with angle pieces put on them to add additional facets. Actually I think I am going to like it the way it looks like it will turn out with these sharp corners. As I think I mentioned before, maybe in the other thread, the flat or straight back will lend itself to and blend well with whatever I am going to need to come up with for a lower profile air/filter box.

ptuomov

I don't know how much latitude you have there, but it's my understanding that you want the sides of the bellmouth as unobstructed as possible, while the bellmouth can be surprisingly close to the opposing wall. Human eye will mislead a bit in making the side obstructions look less important than they really are. These things want to draw from the sides mostly.

Another thing that I believe is that with eight runners feeding one plenum, the plenum volume isn't that critical as long as it distributes well. There's no meaningful Helmholtz tuning effects from the plenum resonance with eight cylinders feeding from the same plenum.

How much power do you intend to make with this engine? That's also an interesting question as it relates to the use of the stock S4 throttle-body element. There's no need to use two up-chutes from the throttle body casting to feed a single plenum, a simpler throttle body element with just one feed tube would probably work well if the feed opening to the plenum is at the center.

Jerry Feather

When I capped myself with my initial criteria I pretty much locked myself out of a lot of very beneficial considerations, or I may have locked myself into some criteria that may be less than desirable for meeting other goals for an intake.

I may end up just bolting this intake on a stock S4 engine, or I may build a stroker and put it on there. The stroker will be based on an S4 block that I have with steel cylinders of 105.5 mm and a Scat six or 8 counterweight crank. I have one of each. I'll have to get custom pistons for the block, probably JE, with 10.5 to one CR, and I will use 968 intake valves in the heads and a set of Colin's somewhat mild cams. It'll probably have a custom exhaust. I would guess the power in the 450 to 500 hp range, normally aspirated.

ptuomov

My opinion is that, if your budget so allows, I'd bolt this intake on a spare head and see how much it flows. Then use those flow numbers to decide what bottom ends would fit the intake flow.

Out of curiosity, what's the runner length from the intake port flange to the bellmouth?

Jerry Feather

I think they are going to end up about 7 1/2 in front and nearly 10 in the rear.

Jerry Feather

I have had this concern myself, but mainly in regard to the vacuum being drawn under no load with the throttle closed and the car decelerating from a fairly high speed, not so much under load, as you suggest, since this engine will not be boosted.

However, when one looks closely at the individual aspects of this plenum the concern for heavier material seems to me to loose its importance. The Bottom of this plenum is made up of 4 components - - the first being the 3/8 inch plate in the center which take up about a third of it. The .063 sheet the rest of the bottom is made of rests on and will be affixed to the 3/8 inch plate. The parts of the bottom forward and aft of the 3/8 inch plate start out as flat .063 sheet, but both are or will be structured with the round tunnels for the MAF in back and the oil intake in front. The structure of all of that probably alleviates the need for heavier material.

The sides of the plenum are so far made out of .063 also. The bottom panel of the sides will be welded to the tubes so that probably adds enough structure there to reduce the need for heavier material. That leaves the flat panel above as the largest "unstructured" part of the plenum.

The front of the plenum and the back will also have enough structure and be small enough to do without heavier material. Keep in mind that the piece of material I now show as the back panel is actually only a pattern out of thin sheet. The final rear panel will also be .063 sheet.

The top of the plenum, not yet pictured, since I don't know it's exact size, will also be 3/8 inch plate. I'll probably machine it in some sort of decorative way, but I think it will be stout enough to resist the pressures that might be involved, in or out.

Finally, I have in mind to connect the top plate to the bottom of the plenum, including the bottom plate, with 4 or more likely 6 posts to resist the up and down movements that might be caused by the engine breathing, or not breathing, as may be the case.

The one thought I haven't had is in regard to a backfire. Given some pictures of plenums on-line that have been blown apart suggests that it may not matter what my plenum is made of - - it can be blown apart at the seams. The thought I am now having in this regard is to possibly devise a burst panel to put on this plenum, probably on the back panel. I'll continue to give that some thought.

The only other concern I have now is the upper portion of the side panels. Whether I need to put something on them to stiffen them or not remains a consideration - - something like Carl did on the top of his 928 plenum. I could very well bolt or weld two plates on these panels to help them hold their shape and not look too crude.

Thanks for the input. It alway helps to stimulate thought.

Jerry Feather

I consider myself an intuitive engineer. Most of what I devise to fabricate is based almost entirely on my intuition. Sometimes my intuition is wrong. In this case, however, my intuition is telling me that your understanding about this is not exactly correct.

My thought is that a bellmouth tube will draw pretty much from the front and with some additional help from the sides based on the bellmouth. Then, as the front of the tube might get closer to an opposing wall the draw from the sides, based on the shape of the bellmouth, becomes more important and will then facilitate much better draw than might a straight tube close to the wall. That is when the limit of side obstructions might become important.

In my case, I have tried to keep the bellmouths far enough away from the opposing walls to allow for good breathing, and particularly since by virtue of the nesting of the tubes with each other, the sides are somewhat obstructed.

I'm pretty much stuck with what I have so far devised. But, thanks for your thoughts about it.

V2Rocket

You might look at the Cadillac Northstar V8 engine for inspiration - they had a spring-loaded flap door on the back of their intake manifold in case of backfire, it sealed tightly with a orange silicone o-ring under the spring pressure.

Burst panel means you have to replace it - the flapper just pops open when needed and shuts again without interruption.

Should still be available from Caddy dealers.

Jerry Feather

Thanks V2. That is actually what I kind of had in mind; then I found more about burst panels on-line. I like the flapper idea the best; and I may try to devise something like that perhaps to go on the lower part of the rear panel that I am now devising. Putting it there will pretty much keep it out of sight so that this intake does not become too cluttered looking.

Jerry Feather

Not much progress, but I did a little refinement of what I have done so far. I cut the A tube off about 3/4 inch and will get it welded back together when I get the E tube done. I am still thinking about shortening the B tube about half inch just so the bell mouth doesn't rest on the floor of the plenum, which it seems to want to do now.

I moved the rear MAF tunnel slot in the plenum floor forward a bit to match the tunnel as I now have it trimmed. Then I cut off the previous bends on the front of the floor and will start working up the pattern for the small front complex panel next.

Carl Fausett

Pretty clever design, Jerry! I hope you have a baseline dyno for that motor so we can see the benefit attained. Good work!

Jerry Feather

Thanks Carl. I learned some things from the thread about the 928 intake you built.