Port Volume Reduction.

[Duk]

Well it would make sense to me, NA you're reliant on pulse tuning/etc to make sure you have the airspeed up (whereas you don't need the max flow figures), but with FI something is actually pushing the air in (dictating the velocity).

Velocity is still dictated by the ports CSA and speed of the piston going down the bore.

Air at sea level/normal atmosheric pressure (1 bar/14.7psi), on a 25*C day weighs 1.18Kg/cubic metre.

If you had a 500cc cylinder opperating at 100% volumetric efficiency, that cylinder would inhale 0.59 grams of air per inuction stroke.

If you were able to supercharge the same engine, using a pressure ratio of 2 (ie 14.7psi of boost) and were able to get the temperature down to 25*C, the 500cc cylinder would inhale 1.18 grams of air per induction stroke.

So mass flow does increase, but it's because the volume is denser/heavier rather than going in faster.

[4AGEKE55]

Interesting thread.

Mass flow can be increased by either higher flow and/or higher pressure.

When it comes to the exact maths to calculating air flow through a particular head porting design, valve shape etc... there is no point comparing what one person has done vs another. There are too many contributing factors to how an engine will behave and what it is designed to do.

Yet, increasing pressure will increase the air speed. If everything else is constant.

The only way for more air to get through is for either the diameter of the greatest restriction to be increased (flow), or for pressure (air speed) to increase.

As Newtons Laws of Physics state that everything wants to balance, hence a high pressure will try to equalise with a low pressure. The greater the difference the more potential energy that wants to equalise with the lower energy. If the diameter that the mass has to pass through is constant then then only way for more to pass is by the speed increasing.

Obviously with valves opening and closing and with all to consider on an IC engine there is more to consider.

Yet increasing pressure will speed up flow.

To test this just go and plug an air tool like a die grinder into an air compressor and see what speed it runs at different air pressures. The pressure will effect the air speed through the turbine in the air tool. If you want to try experimenting with air densitly then try it on days of a different temperature.

Air condenses when cold and is heavier. One of the reasons for intercoolers, the other being colder air is less prone to detonation.

Similarly, turn on a tap. The pressure is constant, yet as the restriction (diameter of the pipe gets larger) more water flows.

Back to engines though, it really depends what you are after. In my opinion for a street motor, all A series heads flow O.K. Prob would go for 20V or small port 16V.

Yet for top end power for dedicated race cars, especially when the engine has FI, the big port head is the best option. It has large enough runners for flow, and pressure from FI will increase air speed. Will have the best mass flow yet may not have much power down low but who is driving a race track below 4000rpm with a 4AGE?

Both pressure and flow decide how much mass flow makes it into the combustion chamber. The more air the more power. Just depends at what revs, how the engine behaves and what the use for the vehicle are as to what size runners and how much pressure should be used.

[oldeskewltoy]

velocity and volume..... in........ AND out.

The intake side isn't as bad as the exhaust side........

[Duk]

Old thread revival!

I did end up reducing the port volume in my big port head that went onto my twin charged AW11 4AGZE engine. With my custom made inlet manifold that looks a lot like a set of extractors in reverse and the reduced port cross sectional area, even without any dyno time (Adaptronic E420c) but just a safe knock free and overly rich tune, she had a very healthy increase in low and midrange torque!
Happily crawling along in 4th gear at 40km/hr and would pull away cleanly and enthusiastically.
In gear acceleration was always fun and effortless! You could just roll on the throttle in 4th and 5th and she would just gather speed at a very enthusiastic rate . And this was with standard supercharger pulley's (so standard SC boost pressure) and below the turbo's boost threshold of about 3500rpm.

On my favorite tight and twisty road, going around corners where I would usually use 2nd gear, 3rd gear is/was better as I could let the greater mid range torque do the talking and not just drive the thing to the red line before the next corner.
And she would jump out of those corners! The first time I drove this road after fitting the new head and manifold, I found myself getting to the next corner after a tight turn much quicker than I thought it would, nearly getting my speed way on into 1 corner 'cause I got there faster than I realized .

Ultimately I would call the whole exercise a success! The aim was to gain more midrange torque via port CSA reduction, to gain as much around town drivability, without strangling outright power. And even though I never put the car on the dyno for before and after, I am happy with the results.
It's a shame the supercharger is dead and now only delivers a few psi to the cause

[TERRA Operative]

Duk.... look for Kai Power. They made(or once made) a flow restricter that part of it slips inside the large port head to reduce the port size. Actually it "individual-izes" the ports



Also, I've actually been @ a Formula Atlantic engine shop, Loynings Engine Service, they did all the machine work on my smallport (but that's another story) - http://www.toymods.org.au/forums/sho...0&postcount=24

The ports on an F/A engine are HUGE

In fact they overbore the ports so much that frequently they'll get coolant leaks through the port walls...



I've also seen the intake valves are placed less then a mm apart (from edge to edge)

That chunk of bigport looks familiar. I've got that exact chunk of head sitting behind me on my shelf.

[NME308]

Yet, increasing pressure will increase the air speed. If everything else is constant.

Hi there mate,
Increasing pressure will not increase the air speed - others have correctly stated this only just slightly higher up the page.

Unlike the water analogy you use where speed has to be increased to improve the mass flow air is a compressible liquid. The mass flow improvements in a forced induction engine come from passing more air molecules past a given point for each unit of time at the same velocity.

To Duk: I like your experiment! If it has not already been mentioned similar port filling has been done by MotoTune Usa on motorcycle cylinder heads for racing applications and while all teams were limited to 101hp as measured by official dyno their motorcycle simply ate the competition due to your own finding of bulk mid range torque and acceleration!

Cheers,
Jason

[Duk]

To Duk: I like your experiment! If it has not already been mentioned similar port filling has been done by MotoTune Usa on motorcycle cylinder heads for racing applications and while all teams were limited to 101hp as measured by official dyno their motorcycle simply ate the competition due to your own finding of bulk mid range torque and acceleration!

Cheers,
Jason

Yes, those MotoTune articles are excellent and eye opening! I really like the one where he adds plasticine to the port of a 600cc bike head until it starts to reduce flow (on the flow bench). The amount of plasticine that he added to what is essentially a small volume port was quite amazing. http://mototuneusa.com/power_news_--..._superbike.htm
I must stress that I only added epoxy to the sides of the ports and tidied up a few little dags here and there. Applying the technique of adding material in the correct area until the flow bench started to show a reduction in flow, would be the ideal way me thinks.

[masterofsinanju]

Interesting thread...


As Newtons Laws of Physics state that everything wants to balance, ...

Aside from the fact that you guys clearly know more about things mechanical as being discussed in here. Newtons laws were about mass and motion.
http://csep10.phys.utk.edu/astr161/l...wton3laws.html
Nothing about balance. Perhaps Bernoulli or Boyle might be more suitable.

[Suavemechanic]

have to agree with you there !
4ageke55 seems to be very clever but is forgetting about the venturi effect of PLACING a restriction in the air path to encourage the air to speed up and become more dense . important rule " liquids do not compress " so all the plumbing analogies are out the window !

[jondee86]

...the venturi effect of PLACING a restriction in the air path to encourage the air to speed up and become more dense.

Anyone with even an elementary knowledge of carburettors, would tell you that as the air speeds up through the throat (venturi) of the carb, the pressure drops. The lower pressure is what draws the fuel from the float bowl. On a technical level I would definitely give this thread a FAIL

EDIT: For the sake of any pedantic readers... yes, I know that atmospheric pressure actually pushes the gas out of the float bowl. So to keep everyone happy, let's just say that it is the differential in pressure that causes the fuel to flow from the float bowl into the venturi throat

Cheers... jondee86

[NME308]

jondee86 for your own sake I hope you are simply referring to a couple of the individual posters and not the concept of the thread itself...

Cheers,
Jason

[jondee86]

The theory and practice of reshaping ports to improve flow is sound. I am familiar with the mototuneusa.com site, and the results they have achieved. Fluid dynamics covers a number of techniques to improve flow, and reshaping bends to maintain laminar flow/avoid turbulence is one of those techniques. As has been shown by mototuneusa, filling ports is a viable way of improving performance, and can give results, difficult, if not impossible, to achieve by traditional porting.

The FAIL is for the people who state incorrect facts, or quote references not applicable to the matter under discussion. This is a Tech forum, so it is not unreasonable to expect people to check their facts before posting.

Cheers... jondee86

[NME308]

The FAIL is for the people who state incorrect facts, or quote references not applicable to the matter under discussion. This is a Tech forum, so it is not unreasonable to expect people to check their facts before posting.

Cheers... jondee86

Cheers,
Jason

[Duk]

The theory and practice of reshaping ports to improve flow is sound. I am familiar with the mototuneusa.com site, and the results they have achieved. Fluid dynamics covers a number of techniques to improve flow, and reshaping bends to maintain laminar flow/avoid turbulence is one of those techniques. As has been shown by mototuneusa, filling ports is a viable way of improving performance, and can give results, difficult, if not impossible, to achieve by traditional porting.

Something which tends to get forgotten, especially when using a flow bench, is the stopping and starting plus reverberation/acoustic tuning that goes on inside the plenum chamber, inlet runners and inlet ports.
Simulating the pressure differential between the cylinder and port side of the valves (a pressure differential that will be constantly changing) and simulating all of the acoustic behavior, would be incredibly difficult on a flow bench. Measuring what the air was doing while all of the pressure differential, air flow speed and acoustic behavior that is going on, would probably be even more difficult!

Seeing supposed flow simulations of 4 or 6 cylinder plenum chambers, where they show constant flow of either 1 or all cylinders at once are anywhere between pointless to very misleading, as constant flow analysis shows none of the acoustic, pulsing behavior that goes on inside the plenum chamber, nor how the pulses from 1 cylinder effect the pulses from the next.
http://www.youtube.com/watch?v=0ft7W_2PbYI is a flow simulation done by 1 of the guys on another forum I'm on. He did it when he worked for Saab, so it was a VERY expensive dynamic simulation software that car manufactures use. It shows the robbing of air from other inlet runners. That's probably OK if the runner being robbed isn't the next 1 in the firing order, but if it is............. Well, pretty sure the true power potential won't be met.



This is my manifold that uses an internal divider between the top 2 (2 & 3) and the bottom 2 (1 & 4) inlet runners.
My logic is that any robbing of air from the adjacent cylinder has them paired with their diametrically opposite cylinder, so it should be less of an issue. Certainly any air robbing should be equal for all 4 cylinders rather than more of an issue on only 1 or 2 cylinders.
The plenum chamber should also have zero flow bias. The air enters the plenum chamber and should have equal potential to flow to any of the inlet runners

[jondee86]

From the look of all the pipework going on, I guess that you have forced induction. That being the case, once the manifold pressure begins to rise, it will most likely start to dampen the robbing of air from adjacent runners. That is, the pressure at the port will be less negative when the valve opens, due to the positive pressure already in the runner. Just a guess of course

Having equal flow into each intake is the ideal, and if I remember rightly, there was a small Toyota a few years back, that had a fabricated intake manifold very similar to yours.

Like this...



Cheers... jondee86