Low profile intake manifold tuned for the 3rd resonance

[Kevin Johnson]

http://www.faqs.org/patents/app/20110168120

[englertracing]

How's about building a 180 manifold for 1st resonance and placing the plenums outside of the valve covers >:)

[ptuomov]

How's about building a 180 manifold for 1st resonance and placing the plenums outside of the valve covers >:)

You mean replicating the 1986 Porsche 928 S3 manifold, but with dual side feeders and with more appropriate runner diameters and lengths? Has crossed my mind. Here's the manifold I am talking about:

[nickmckinney]

One can go back to the early 1960's on this idea, I actually owned one of these:

[ptuomov]

One can go back to the early 1960's on this idea, I actually owned one of these:

Yes the Chrysler cross ram. Isn't one of the people who was on the development team on the board? In terms of functionality, the main difference between that Chrysler manifold and the 1986 Porsche 928 S3 manifold is that the Porsche manifold actually collects equally spaced pulses in the same plenum, so it's a true 180-degree manifold.

The S4 manifold that I currently have on the car is similarly a true 180-degree manifold, and it also has a resonance flap that alternates between single plenum and dual plenums. Sounds great then? Not so much, because the manifold is cramped in a really small space and is full of awkward turns. It works very well 2000-5000 rpm and not very well after that.

[Kevin Johnson]

For some reason, the factory made the inside cylinder runners longer. The story doesn't tell why.

Well, there is a substantial amount of information that you are missing from "the story". You cannot expect them to be explicit. Examine the photos more carefully.

Note that the carbureted version used equal length runners. Note that early versions of the injected engine used inner runners that were joined. This points to a distribution issue with the manifold or possibly NVH taking precedence. They got pretty excited about the magical effects of relocating the battery, remember. See "V4" on page 93.

[nickmckinney]

...because the manifold is cramped in a really small space...

Thats the main handicap of all street V8 intake manifolds, inline engines do have the advantage here especially with fuel injection designs. No matter what you design for your combo the space factor will hurt its maximum output. The question becomes do you put more bends to make longer runners or keep them short and straighter, and how to divide the space between runner and plenum volume because one or the other (or both) will be smaller than desired no matter what.

[ptuomov]

http://www.faqs.org/patents/app/20110168120

That design has the downside of having unequally distributed pulses hitting a smallish plenum.

I think it would be better to basically copy the Ozmo Engineering cross-ram manifold, which has improved pulses.

[ptuomov]

For some reason, the factory made the inside cylinder runners longer. The story doesn't tell why.

Well, there is a substantial amount of information that you are missing from "the story". You cannot expect them to be explicit. Examine the photos more carefully.

Note that the carbureted version used equal length runners. Note that early versions of the injected engine used inner runners that were joined. This points to a distribution issue with the manifold or possibly NVH taking precedence. They got pretty excited about the magical effects of relocating the battery, remember. See "V4" on page 93.

What photos and what pages? i am not following.

The carburetor 928 manifold in the 1970's didn't have much to do with the 1987 fuel injected manifold. There were multiple complete different designs in between the two.

If you know why the 1987+ S4/GT/GTS manifolds have long runners for the inside cylinders and short runners for the outside cylinders, please tell us. I can guess many reasons, from the engine sound to broader torque curve, but I don't know why they did it nor do I know the reason behind it. I am just noting that usually the V8 manifolds have the short runners in the middle, and one of the rationales in addition to packaging that I've heard is that the inside cylinders run hotter and therefore are more knock prone at the torque peak.

[Kevin Johnson]

Look at "the story": Project 928

For some reason, the factory made the inside cylinder runners longer. The story doesn't tell why.

Well, there is a substantial amount of information that you are missing from "the story". You cannot expect them to be explicit. Examine the photos more carefully.

Note that the carbureted version used equal length runners. Note that early versions of the injected engine used inner runners that were joined. This points to a distribution issue with the manifold or possibly NVH taking precedence. They got pretty excited about the magical effects of relocating the battery, remember. See "V4" on page 93.

What photos and what pages? i am not following.

The carburetor 928 manifold in the 1970's didn't have much to do with the 1987 fuel injected manifold. There were multiple complete different designs in between the two.

If you know why the 1987+ S4/GT/GTS manifolds have long runners for the inside cylinders and short runners for the outside cylinders, please tell us. I can guess many reasons, from the engine sound to broader torque curve, but I don't know why they did it nor do I know the reason behind it. I am just noting that usually the V8 manifolds have the short runners in the middle, and one of the rationales in addition to packaging that I've heard is that the inside cylinders run hotter and therefore are more knock prone at the torque peak.

[Stef]

I'm with Brazilian. Boost is overwhelmingly more effective than pressure tuning. Also, over a wide powerband the tuning benefits of runner length cancel out and as well the resulting torque peaks and valleys will make for driveability issues on a high-power application. Better to just go with very short runners and a 'whatever fits' plenum.

Well we know short runners work with a turbo, but does it maximize the engine?

I can smooth out any natural torque peaks and valleys in the mid range by compensating with the manifold pressure.

Right now, I am running the stock manfold which has the following runner lengths, including what is inside the head:

Inside cylinders: 12 inches + 4 inches in the head = 16 inches total runner length
Outside cylinders: 8 inches + 4 inches in the head = 12 inches total runner length

For some reason, the factory made the inside cylinder runners longer. The story doesn't tell why.

It is simply to broaden the power band as much as possible using the primary runners. It's used on the Porsche, Superbikes, Can-am big blocks, etc. I've used it on engines with success. A further boost to the power curve is provided by the 180* arrangement of the runners and plenums providing a low rpm resonance boost.
It's described in Porsche patent # 4641610.

Most production turbo engines use either the 2nd or 4th harmonic lengths. There are some exceptions like the anti-resonance manifold of the latest Porsches but they're rare.

You will not get a low rpm boost unless you use the 180* system or a flat plane crank. So if you settle for a normal 360* type intake it will have a single resonance boost point. Any peaks and troughs will be caused by what happens during the IVC period the amplitude of which will be dependent on several factors. The same will happen if you have all cylinders of one bank connected to a plenum like a cross ram manifold or similar.

You will need to decide what harmonic length you can package keeping in mind you want them as straight as possible. A well designed runner entry and suitable plenum sizes can then follow. I would base the plenum shapes on some of the LeMans type engines; AER V8, Lancia LC2, etc. Most of these are flat plane but they have good air distribution. Include a balance pipe between the two.

[ptuomov]

Stef - Thanks for your detailed post. Indeed, the S4 manifold on the car and the S3 manifold in the pictures I posted earlier use the scheme in that patent. So basically my options appear to be a single plenum, short-runner manifold or replicating the factory manifold with different size (diameter, length) runners with hopefully more gradual bends.

[Kevin Johnson]

For some reason, the factory made the inside cylinder runners longer. The story doesn't tell why.

It is simply to broaden the power band as much as possible using the primary runners. It's used on the Porsche, Superbikes, Can-am big blocks, etc. I've used it on engines with success. A further boost to the power curve is provided by the 180* arrangement of the runners and plenums providing a low rpm resonance boost.
It's described in Porsche patent # 4641610.

Good citation. Within it a patent is cited from the mid 1930s that obstructs Porsche from patenting the longer (varied and interconnected) runner versions on the single plenum used in the development 928 engines over a decade prior. If that in particular was patentable it would have been filed for in 1977 when Project 928 was published, like the bedplate oiling technique. The K-Jetronic or continuous system was described as being used in experimental platform V4 which indicates it was a manifold air distribution/balance problem. Later the 928 went to digital multipoint which would allow reasonable support for claims found in the patent.

[ptuomov]

As a purely academic exercise, I sketched a 180-manifold that might fit under the hood. I don't have the skills to make this and I don't know if the runner lengths would really work any better than the stock manifold. The turns would be pretty large radius and runner lengths could be made about equal.

IMG-20130504-00034.jpg

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[ptuomov]

Last one:

IMG-20130504-00033.jpg

I am babysitting a nine month old who's helping me out with the sketches...