BC

(I thought you) measured it recently, but this is not to give me more space - its to reorient and completely change the place at which air enters the runners - and in that way completely remove the side plate restriction, as well as the Throttle body position, which I don't like,

I want to make two of what I showed, and then put a D plenum on each side, with a forward facing entry for air.

ptuomov

I measured the plenum volume to be about 1.85L per side. However, the question I was asking is how much a plenum spacer that is say 10mm increases the plenum volume. For that computation, one needs the area of the plenum opening. I was guessing that you might have that available if you have the geometry programmed.

worf928

Along those lines, let's not forget that thinking about air as if it is an incompressible fluid only gets us the wrong answers after a certain point.

I'm armed with college-level fluid dynamics and English as a second language. But, unlike Tuomo, the powder in the bullets in my gun is so old that it won't ignite and I'm left with only the memory of what it sounded like...

Nevetheless, to me, simplifying the contexts of N/A and FI to just pressure sounds like modeling air as one would water. Whereas seeing what it does on a flow bench is an observation of air acting according to its nature as a compressible fluid.

simos

It's the piston which is sucking or pulling the air into cylinder. Top of this is the intake pumping process which is actually very strong. Pressurized plenum may help there, but isn't the major thing.

I like the following little document very much, don't know who wrote it but he really knows the stuff: http://www.google.pl/url?sa=t&rct=j&...Wu_98Q&cad=rja


When the valve opens, the air doesn’t flow in, it decompresses into the low-pressure region. All the air on the upstream side of the moving disturbance boundary is completely isolated and unaffected by what happens on the downstream side of it. The air at the runner entrance does not move until the wave reaches all the way to the end. It is only then that the entire runner can begin to flow. Up until that point all that can happen is the higher pressure gas filling the volume of the runner decompresses or expands into the low-pressure region advancing up the runner. (Once the low pressure wave reaches the open end of the runner it reverses sign, the inrushing air forces a high pressure wave down the runner.)

Conversely the closing of the valve does not immediately stop flow at the runner entrance, which continues completely unaffected until the signal that the valve has closed reaches it. The closing valve causes a buildup of pressure which will travel up the runner as a positive wave. The runner entrance continues to flow at full speed, forcing the pressure to rise until the signal reaches the entrance. This very considerable pressure rise can be seen on the graph below. At the closing of the intake valve, pressure rises far above atmospheric.
It is this phenomenon that enables the so-called “ram tuning” to occur and it is what is being “tuned” by tuned intake and exhaust systems. The principal is the same as in the water hammer effect so well known to plumbers. The speed that the signal can travel is the speed of sound in the gas inside the runner. The boundary between the wave affected gas and unaffected gas could be compared to the event horizon of a black hole.

This is why port/runner volumes are so important. The volumes of successive parts of the port/runner control the flow during all transient periods. That is any time a change occurs in the cylinder whether positive or negative. Such as when the piston reaches maxumum speed half way down the stroke.
The wave/flow activity in a real engine is vastly more complex than this but the principle is the same.

At first glance this wave travel might seem to be blindingly fast and not very significant but a few calculations shows the opposite is true. In an intake runner at room temperature the sonic speed is about 1100 feet per second and will traverse a 12 inch port/runner in 0.9 milliseconds. The engine using this system, running at 8500 RPM, takes a very considerable 46 crank degrees before any signal from the cylinder can reach the runner end. 46 degrees during which nothing but the volume of the port/runner supplies the demands of the cylinder. This not only applies to the initial signal but to any and every change in the pressure or vacuum developed in the cylinder.



As John pointed out and some of my previously sent documents proved, the vawe pulse effect will change the steady flow effect the way, that even not so well flowing port would still work quite well...

Also, the NA and boosted engine will work under same physical laws what comes to plenum and intake path functionality. The main difference is the compressed air in boosted application, which means that it has higher density.The velocity of intake port in both cases will be the same, but VE will be higher as in boosted application the air density is higher.

When velocity in port will exceed 0,55 mach, the port starts to choke. In this case, the velocity will still increase, but air starts to stretch and result is that the air has less density. This is the point, wehere power starts to drop quickly.

mark kibort

Well, I maybe didn't make myself clear enough. Im not talking about the ITBs, as I understand that they might raise up the entire intake plenum area. no ITBs, means the intake inlets can just attach to the stuff like carl has made. It looks like it fits, and then the throttle body would mount out front,using a stock MAF. if it didn't fit, then just close off , like carl has done with his plenum design for the blower, but use it in a NA application.

this will solve all the problems and give some big HP gains.

as far as the 5.4 liter making more power than my engine.... my engine is fed by all stock , no change, components. im sure with a shark tune or some changes to cams, some decent gains could get it up to 400-410rwhp like we have seen on other 6.4 liter engines. But, the intake is the element that is most interesting as Anderson and Fan bolted on a type similar to what im suggesting and gained near 100hp.(no other changes). so all the theory in the world aside, the gains were made with intake only over the stock stuff.

As far as the flappy, again, its only needed for drivability , in racing or dyno comparisons for peak HP, its meaningless, as it only helps below the "racing" rpm range (i.e. below 4500rpm)

as far as the semantic discussion between GB and others, its the pressure that does the work, vacuum does nothing. air moves to differential pressure. forced or not, the flow acts the same.


Mk

ptuomov

I think the document you linked to is peddling the usual Hot-Rod Magazine bull****. The intake valve being closed in a well tuned engine operating at the tuned rpm is not going to cause a meaningful pulse. This is because the flow has already stopped by the time when intake valve closes. Why? If the intake charge would still be flowing into the cylinder, we'd wait longer to close the valve! Instead, what causes the pressure pulse is the piston slowing down and reversing near the BDC. Pressure traces, whether simulated or measured, conclusively debunk the Hot-Rod Magazine "intake valve closing causes the pressure wave" myth.

Agreed.

BC

Then yes, let me check.

tveltman

Apologies if I have missed it, I haven't made it through the whole thread, but hasn't someone set up an 8-channel WBO2 setup in the past, one for each cylinder? If you are going to throw $$$ at a project, couldn't you just infer the air flow rate into the cylinder from the fuel map and the mixture reading on the WBO2? You could even individually calibrate the injectors so you could correlate injector pulse time to a precise fuel dose and remove that variability. Take a bunch of readings at various constant RPMs (to average out sensor response time), and then you get data on all 8 channels which you can massage to give you flow numbers. Of course I suppose that porting/polishing/whatever tweaking you want to do would be a time-consuming process to evaluate by trial and error, but this method ought to at least show you the standard deviation for the cylinders, no?

danglerb

If your FI brain is "smart" you can do a cylinder balance with a single WBO2 by tweaking the injector time one cylinder at a time and looking at the changes.

+1 on what PT said, its piston motion not valve closing, unless the timing is screwed. Ideal is zero flow at the valve as it closes.

ptuomov

Related idea discussed here: https://rennlist.com/forums/10484429-post99.html

jorj7

Pulled the intake on my Cayenne S yesterday with Van, to replace the coolant pipes (thanks
Roger for the parts, I appreciate the fine support we get from our 928 venders) and it's a interesting looking part.



Something like this might work well on the 928.





George
90 S4 Grand Prix White (Murf #5)
94 GTS 5-Speed Midnight Blue
06 Cayenne S Havanna/Sand Beige (PASM)
http://928.jorj7.com

jorj7

I've had that problem, ie different color plugs. Engine before my current one...



George
90 S4 Grand Prix White (Murf #5)
94 GTS 5-Speed Midnight Blue
06 Cayenne S Havanna/Sand Beige (PASM)
http://928.jorj7.com

IcemanG17

George
Your plugs are interesting.....I'd say far left is about perfect, maybe a touch rich
#2 is FAT silly fat......way too much fuel
3 looks lean to me
4 isn't bad, the best of the group........

I read several articles about "reading" plugs.....what they recommend is getting a jewelers loop (I'm unlucky my wife has one) and looking into the base of the white conductor insulation where it meets the base....that is known as the "fueling" mark...it tells you what your AFR is at high load...of course I don't remember which colors mean what.....but drag race guys have it down to a science

for what its worth....mine all look like #4

ptuomov

I can read tea leaves, palms, or spark plugs, but the logical explanation for why the second plug from the left looks the way it looks is oil deposits. Can't feel the texture in the picture, of course, but it looks like oil problem. It would be a logical explanation as well since your engine had all sorts of oil control problems before Jim Morton rebuilt it right with his custom ring pack, after which I assume you didn't get spark plugs looking like that anymore.

I don't think these plugs are very informative about the intake manifold air distribution.

UpFixenDerPorsche

These are the results to which I referred in my post of a day ago regarding intake plenum resonance.

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