Carl Fausett

I'm so glad to hear that! I'm glad you did. That is why i publish these things as I make them.

For others; here is a link to two of them that I have done:

16V: http://www.928motorsports.com/instal...folddesign.pdf

32V: http://www.928motorsports.com/instal...oldarticle.pdf

Mongo

Reminds me of the pop off valves for 70s and 80s 911s you can install to prevent blowing up airboxes.

Jerry Feather

I made part of the pattern for the front panel. It took two iterations, but the final one fits nicely, even though it is a bit short. I'll probably make a third one that goes all the way to the center seam, but that shouldn't be too much trouble just to copy what I have so far. Then I'll do similar for the pattern for the last piece for the front.

I had kind of hoped to make the front panel in one piece, but the only thing I would save is one short weld in the middle on the bottom front, and the extra trouble in forming it at so many different angles is just not worth the effort.

I also found a nice piece of 3/8 inch plate for the top panel, and now that I am so close to having the measurements I may start machining that this weekend. I also found a nice piece of .090 aluminum in my supply and think I might make the rear panel out of that since I am giving serious thought to fabricating and including one or two blow off valves in the fashion suggested above.

Here are some pictures of the progress.

Carl Fausett

Excellent fab work. I apologize if you have already mentioned this - but will this be boosted or is it a NA manifold?

Jerry Feather

NA.

Carl Fausett

Excellent. I expect good results!

Jerry Feather

Thanks again, Carl. I appreciate your outlook. My outlook has been for "good results" also; but I think what you might have in mind for results is probably very different from what I have in mind.

I started this project, even before Hans came up with his beautiful intake bases, but that start was pretty much only in my head. With Hans' bases I was saved a significant amount of development and fabrication, and they took me is a very different direction from what had been developing in my mind.

Then I began to post my development and fabrication in his thread about the bases, mainly in response to his inquiry about what people were going to do with the bases. I moved my development to this new thread mainly because the other thread seemed to be getting kind of cluttered and long, and I think what I was doing up to that point pretty much answered the inquiry.

The results that I had and still have in mind is an intake that will function about as good as the original, or even just close to it, and mainly that will fit under the hood as it gets lowered in the custom work I plan. I had given almost no thought to the criteria that I think you and the few others who have taken on an intake development have developed around, so any results beyond fitting the new limited space and functioning at all will be icing on my cake, or gravy on my potatoes.

My purpose in posting my development is primarily to show how one might go about designing and fabricating anything similar, or even not similar, but using these kinds of materials and methods. I myself learned a lot about this kind of thing back in the day reading car magazines and watching others doing various fabrication techniques. I'm sure no one else will ever build an intake even roughly similar to mine, but there may very well be things that someone else might pick up on in this thread that gives an idea about how to develop and fabricate something else.

Thanks again for your input and for your encouragement.

Carl Fausett

What do you calculate your plenum size to be? Have you decided whether this is going on a 5.0L motor, or the stroker you talked about?

Jerry Feather

I could probably calculate it pretty closely depending on whether or not the inside of the intake tubes is part of the plenum or everything outside of the tubes but inside the box. Then how much of the throttle body should be included in the plenum?

I'm a long ways away from deciding which engine this might go onto. It will likely be a stroker in any case since I don't have anything but an engine core to rebuild or put an otherwise used engine out of the car that will be donating much to finish the custom car; and I think I will want a fresh engine for it. And, I think any engine I build will be stroked with either 968 pistons or custom pistons in the 105.5 mm block.

Carl Fausett

The area inside the intake runners would not be considered part of the plenum. That would be from the bell mouths down.

The good news is that plenum sizing has a lot of give-and-take in it, so you aren't too likely to run into trouble unless yours is way too small (it isn't) or way too large (it might be). But I am only looking at pictures and without dimensions and doing some math, I cannot tell.

What happens if a plenum is too large is you get some run-on after you snap shut the throttle, that is, there is so much air in the plenum that even after you close the throttle the engine keeps going for a moment before it decels. Poor throttle response and bad for road racing and street driving

But like I said, it takes a fairly extreme case to cause that and I do not see your plenum as being so big as to be a problem. Certainly if you bolt this to a stroker motor, this is even less of an issue. No worries!

More important than plenum sizing is to vary the intake runner lengths a bit to promote a nice long power band from the engine. I discussed the Helmholtz effect in my white papers, and how to apply it to the decision on how long to make your individual runners. Let me know if you have questions.

I will be out from now until Monday morning. Happy weekend everybody!

Jerry Feather

Thanks again Carl. That is all very insightful and encouraging. I think the plenum would measure 19.5 by 8.5 by 4.5 if it were a simple rectangular box. Given it's irregular shape those are pretty good approximations of the averages in each respect. That comes to 745 cu inches. The TB throat downstream from the throttle plate is approximately 158 cu inches in volume. The tubes average 9 inches, being from 7.5 to 10.5 inches long to the lip of the bellmouths, so at 2 inches in diameter their combined volume is about 226 cu inches. The net volume is 677 cu inches. How do you think that fits in the performance criteria you have in mind?

Edit: The volume of the tubes that I deducted from the plenum is incorrect since I used the volume of the entire length of the tubes, but about 2 inches of each tube is outside the plenum. The volume of the tubes outside the plenum is about 50 cu inches, so the net volume of the plenum is very close to 725 cu inches.

V2Rocket

Don't know what you plan to use for air filter setup in your hotrod but you might be able to borrow a design feature from Subaru...
On my Outback (2.5L DOHC 16-valve) there is a pretty large central plenum feeding the 4 long legs of the "spider". Since this is a car meant to be driven easily by soccer moms they needed it to be smooth at throttle tip-in, so they put a big air tank/resonance chamber (not for power tuning but for acoustics) immediately at the other side of the throttle body with the idea being that there is a large volume of atmospheric pressure air right there at the TB input for when the TB changes position, rather than waiting for "extra air" to have to rush in all the way from the air filter.

Don't know quite how well it helps but the car is certainly very smooth to drive, and they used this concept in one form or another for the next 18 years after my car was made.

ptuomov

In my opinion, if all eight cylinders are feeding from the same plenum in a fuel-injected V8 engine, the plenum volume doesn't matter to pulse tuning. The plenum just has to be large enough that the trumpets can feed without too much obstruction.

Jerry Feather

You have suggested that twice now. When I started this development I didn't have such an opinion, but I might take credit for hoping that the same might be true. I think I was hoping that with the fairly complex shape of the skin of the plenum, with the plenum being kind of filled with tubes all over the place and with air being let in from two directions, that any kind of theories about resonance, pulses, waves and such would be pretty much of little use or concern. Therefore, I still hope your opinion is correct.

As to the S4 double air inlet to the plenum versus a single throat at the center, perhaps from as S3, I didn't give that much thought either. As it turns out, however, I now think that with all 8 of my tubes actually crossing the inside of the plenum and feeding off of air along the opposing outer wall of the plenum, that part of the plenum might very well be the best place to introduce the air rather than from one central opening as you suggest since that one opening would actually be introducing air from behind the mouths of all 8 of the tubes, whereas my use of the double opening of the S4 introduces that air basically at the front of the tubes on each side. Does that make any sense to you?

V2Rocket

Next OEM to borrow inspiration from: Ford.

A single throttle was deemed sufficient for this engine, the Ford 5.4 SVT Cobra-R...
almost 400 hp from an N/A 5.4L DOHC engine, in 2000! And it met emissions and drivability standards, too!