You are completely mistaken. Gaseous particles don't follow the exact behavior of liquid state particles - i.e. liquids are not compressible. Otherwise, there would be no resonance tuning at all for intake or exhaust.

 

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Liquids, Solids, and Compressibility

Monday, September 30, 2002



name Jared K.status studentage 17Question - How come, when most solids are more dense than liquids,liquids are not compressible, but most solids are?Both liquids and solids are compressible -- only slightly, but compressible nonetheless. The compressibility of solids is generally smaller(they resist deformation more, because compressibility is defined with anexplicit negative sign) than for liquids by ~ 3X. However, there is overlapbecause other factors are also important. The compressibility: K = -(dV/dP)/V varies with temperature, pressure, and other variables, so itis quite difficult to measure. The compressibility of solids, especiallysingle crystals, is even more complicated. Assume the atoms in a crystalhave coordinates (x,y,z). The crystal structure is often not isotropic, i.e.the arrangement of atoms/molecules in the 'x', 'y', and 'z' directions isnot the same. So an increase in pressure in the 'x' direction results in aDIFFERENT change in volume in the 'y' and 'z' directions. The same is truefor the other coordinates. So the compressibility now has NINE components --Kij where both 'i' and 'j' can equal 'x', 'y', and 'z' -- i.e. componentsKxx, Kxy, Kyx,..., Kzz. The term Kxy, for example, measures how thedimensional change in the 'y' direction if I squeeze in the 'x' direction.For some crystals Kxy may not even equal Kyx!! Such nine component arraysare called "tensors" and they have a whole "algebra" that governs theirmathematical behavior.Vince Calder============================================ ==================Liquids are compressible. They just do not compress much compared to gases.


Richard E. Barrans Jr., Ph.D.Director of Academic ProgramsPG Research Foundation, Darien, Illinois========================================== ====================

 

Water IS compressable; just to a lessor degree and alot more pressure requirements and temperature considerations. Only in the lab, are they not.

As for my explaination regarding airflow, you obviously did not read it carefully.

 

Interesting results, this was one of the mods I was looking at.
dduncan, Have you driven the car yet? How much different does it feel?

 

The very minute compressibility of liquid (<<1%) is of absolutely no consequence. For all intents and purposes liquids are non-compressible. Gas is highly compressible and that is why gaseous particles do not all follow the flow in the intake tract the way water would flush down a toilet.

 

It would be interesting to know if simply the engine didnt "adapt" to the RSS Plenum and therefore the results were poor.

It would be a real shame if my RSS Plenum is posing a negative effect to my overall performance that I have with my AWE setup.

I think we need a few more case studies to see if this is really true....

 

This was talked about on the Turbo forum a bit . The stock ECU took a bit of time and the GIAC was expected to be quicker based on some assertive driving .

I noticed the difference (with GIAC) after about 100 miles of normal driving but a bit more assertive to try and reduce adaptation time.

 

more of a 5% drivetrain/powertrain loss

 

The drivetrain losses on dduncan's car will be the same percentage as everyone else's (Unless the gearbox manufacturer has developed a special low-loss, straight-cut gearbox for this car)! That will be 16% give or take a percentage point.

The fact that his base runs are on the (very) high side of normal either means that 1) AWE's dyno is reading high (all dynos read differently) 2) dduncan's car is just a particularly good example straight from the factory or 3) and most likely - both.

The important bit is the percentage increase: 27/323 or 8.3% If his engine was producing 355BHP stock, then it now produces 384BHP. Nice result! If it was producing around 374BHP stock (as would be the case if AWE's dyno isn't reading high) then it now produces 405BHP. Awesome result! The reality will probably lie between these extremes.

 

just wondering, how come the line on the dynograph is fluctuating so much?

 

So my statement "water is compressable" remains correct.

So, are you suggesting that the wave pulse in the intake caused by resonance is a result that the air becomes compressed? I really have no idea why you are talking about the compression of air and water. It's a nice conversation but how does it apply to this conversation?

 

Mainly the problem is in the statement that all the air flows only in 1 direction - that is not true. Because gaseous particles have alot of space between them, gases are highly compressible and they can more freely without the kind of motion constraints of liquids - like pulling a slinky in 1 direction versus pulling a rope, the coils of the slinky can still move back and forth despite being pulled one way.

The gaseous particles will reflect off the closed intake valve and bounce backwards towards the plenum. Some of those backward reflections then will reflect again off the density of the incoming plenum air but some will go all the way to the opposite intake tract before reflection again. This creates a very long tract for reflection (opposite intake tract) which is possibly why the RSS plenum is actually dropping more power at the 5k range - the long reflection path has been cut in half by the curved plenum. The Porsche design creates a long tract in half the space essentially. It should not be too hard to calculate the length of an intake tract which improves resonance tuning at 5k rpms in this sized engine.

 

I think you are confusing sound resonance frequenzy with actual air movement. Once air is in one intake distributer, it never crosses over into the other. Such a movement of air would be impossible unless one bank of the engine had open intake valves and the other side had closed intake valves at the same time. Remember that the mass of air available in the intake is less than 50% than total cylinder mass.

And increased pressure applied to a gas does not always translate into compression of the gas. Maximum velocity musy be acheived before compression begins.

 

Lets back up a little bit

1)sound is carried by air movement. Air movement is necessary for sound - there is no sound in a vacuum (outerspace). So you cannot dissociate intake resonance tuning (~soundwaves) from air movement - it IS air movement.

2)because air/gas is so low in density, waves of air/sound can pass thru each other with relatively little resistance, unlike water or liquid. That is why pulses of reflected air in the intake will bounce off the intake valve and reflect back thru the incoming intake air

3)gas always moves from low pressure to high pressure. You cannot increase gas pressure without gas compression. Using P=nRT/V, for P (pressure) to increase holding n(# moles) R(natural gas constant) and T(temp) the same, V(volume) must get smaller - i.e. compression of the gas. The bigger the pressure gradient, the faster the velocity of movement - but there is no velocity until there is pressure/compression

 

I have no idea what your point is. Like I asked before, are you stating that air is being compressed in the intake? Yes or no?

I cannot be any clearer than stating that once the air is in one intake, it WILL NOT, CAN NOT ever reach the other intake. You really should study fluid dynamics. The laws are quite a bit different than they are in a closed environment. An NA engine DRAWS air. The air is not being puhed into it.

Pressure does not mean compression of a liquid or a gas. Gas and liquid will always follow the path of least resistance. You are trying to tell us that, somehow, a cylinder on one bank that is trying to suck air in is ignored and a cylinder trying to suck air that is located on the opposite side of the engine will take it instead.

So, how about specifically answering my question? Does the air inside the intake become compressed because of resonance or any other factor? This will at least give me an idea of whether to continue with the discussion.