JGheen said:
Nathan, just to answer your question, airflow and boost pressure are two different things. The air flow through the engine is limited by the cylinder head.
Yes and no. Air flow through the head is most affected by the cylinder head (and valve geometery, timing, etc. ) but there's plenty else that will ultimately limit how much air can be stuffed through that mill.
If you throw on a aftermarket intake and exhaust manifold onto the engine with doing nothing to the head ports then you will still have the same airflow through the engine as the ports are restricting you from moving any more air.
Wrong. If you relieve a restriction at any point in the inlet or exhaust systems of the engine, you will make a positive effect on airflow and power. Again, some parts count more than others, but all contribute at least a little.
However, when it comes to boost pressure you can be running 30 psi or 40 psi and you will have the same airflow as before due to the head ports restricting it.
Wrong. The difference in airflow assuming the temperature of the air and mechanical restrictions remain the same in both cases is 13% greater. It's almost a 29% increase in pressure, but only a 13% increase in flow. No matter what restriction the heads, intake, turbo, muffler, etc create, the airflow WILL be 13% greater. Period.
You could even be running 100 psi and will still get the same airflow.
Running 100 PSIG instead of the original 30 PSIG would yield a 60. 1% increase in airflow. Wrong again.
The turbo flows air as well as compresses it, but again it will only flow as much air as the cylinder head ports will allow.
No, read the above. As long as it's flowing a compressable fluid (hello air) an increase in the pressure it operates at will accompany an increase in flow through a fixed restriction. Don't believe me? Go open a high school physics book.
Once the turbo reaches its max airflow due to the ports of the head restricting it, it will continue to compress the air, of course until the wastegate opens allowing the exhaust to bleed off and not spin the turbine wheel any faster creating more compressed air.
Wrong. A turbo's limitations are only how much pressure ratio it can produce at a given thermal efficiency. Again, note that it's a PRESSURE RATIO, not a finite flow number or boost pressure. Behold the wonderful world of compound turbocharging. A centrifugal compressor (i. e. turbocharger or centrifugal supercharger) will stall/surge as it reaches its maximum pressure ratio. Since the turbo does NOT limit the engine airflow, your statement about the wastegate's role is completely incorrect. The wastegate's purpose is to prevent the turbocharger from operating outside it's envalope of efficient operating conditions. Try to push it too hard by holding the wastegate shut too long hurts performance as it superheats the air, lowers the inlet charge density, decreases power, creates more of an exhaust restriction. In fact, the turbine housing is the biggest restriction in a turbocharged engine, and you're completely oblivious to the fact.
A given port area will only move so much air as the volume of the ports will allow.
Wrong. And you've never opened a physics book in your life. You're never too old to learn. . . . .
An example of this would be the arguements of the Banks High Ram and Twin Ram intakes flowing more air into the engine. They provide more volume of air on the intake manifold to breathe from, but they do not allow more flow unless the cylinder head port volume has been increased as well.
Absolute rubbish. I suppose you're saying that Banks Engineering is lying about the power gains they claim the intake will create?
I personally believe that the Twin Ram intake on my truck does not flow any better than the stock single ram, but it does distribute the air more efficently to all cylinders and not starving cylinders 4,5 and 6 for air.
Sure it does, but unless you've made some changes in your fueling, you'll never know the difference! A diesel engine is an AIR HOG. In most cases, you've got more air than is needed to support a clean burn which is why a torque plate or power chip device yields a great deal more power than does a fancy air cleaner or exhaust system. However, once you've fueled it up to the point that the mass of air lags behind, it's then that you start to see improvements not only in power by increasing airflow, but reductions in EGT and tailpipe opacity. You have nothing other than your butt dyno to tell you if it's made any difference or not, and you're basing your entire theory of operation around the fact that you CAN'T tell the difference.
Now when it comes to RPM, obviously airflow will increase due to engine speed but again it will only flow as much as the head allows and if we want to get really technical airflow can improve with how much the valve opens, but I am sure Cummins has flowed their heads with the appropriate lift for max flow with the given port volume.
Guess what. . . . with an increase in RPM, volumetric efficiency goes down. Know what that means? It means that it's better to move more air at a lower RPM than it is to move the same amount of air at a higher RPM. Does this make any sense to you?
You can have more or less flow through a cylinder head with a given valve lift but if the valve opens too much it is restricted by the port volume.
And an expert in cylinder head design too, I see. Actually, the area just behind the valve seat in the port is the biggest bottleneck, not valve size or port cross-sectional area.
If the valve opens too little the valve restricts the airflow.
Did you figure that out all by yourself?
Regardless of the airflow you can throw any number of boost you want at the engine but of course only as much as the head gasket will take, but pressure is not volume dependent.
Another bogus statement. Boost doesn't kill head gaskets. Uncontrolled cylinder pressure kills head gaskets.
Look at our hard injector lines for example. I can't remember, but they have something like 1500 psi (maybe more, I can't remember off the top of my head) of pressure running through them and they are only like 1/4" in inside diameter.
What's your point?
Hope this explaination helped in your understanding of airflow through an engine.
Joe
You need to get at least a fundamental understanding of fluids before you go trying to engage somebody else in a technical ******* match on the internet. I'm sorry if I've offended anyone, but such blatant proliferation of absolute HOOOEY is a major pet peeve of mine. You're doing nothing but confusing people who honestly want to learn, and making yourself feel like a bigshot in the process. Keep it up, there's enough of us here with the education and background to make you wish you'd have left well enough alone.
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