| engine breathes through its RPM range. It can be broken down into different RPM intervals and analyzed at each point. The value at a given point represents the percentage of air mass that makes it into the cylinder vs. how much air mass is contained within a volume equal to the displacement of the cylinder at atmospheric pressure. This number kindof loses its point when discussing forced induction though. It can still be calculated using conventional formulae but will result in a >100% figure. In some naturally aspirated engines, greater than 100% VE can be achieved but this usually only occurs at a single narrow range of engine RPM - when the tunnel ram effect in the intake and exhaust scavenging work together to literally force more air mass through the engine than what its native displacement dictates. For forced induction you can correct the formula to take the pressure ratio into account and determine what the baseline air mass should be at a given boost pressure, and then take your air mass measurements and compare. But even with this approach there are other factors involved, such as the air density variations due to temperature. Then you'd have to take measurements of the air temperature at the intake manifold to further correct your maths. Bottom line is that VE is just a calculated figure that doesn't carry that much weight to it - it is kindof like the bragging rights side of dynocharts. VE does have its place though in a very specific way - it is used extensively in MAP-based systems (speed-density, if you will). Those EFI systems incorporate a VE table into the ECU which is used to determine the air mass entering the engine for a given manifold pressure and air temperature (and from the air mass the ECU can determine the fuel mass delivery required to achieve a target air/fuel mixture ratio). For us, VE is just a concept that gets thrown around from time to time and doesn't carry much meaning. What we are mostly concerned with is mass flow as this focuses specifically on the number of O2 molecules you are packing into the cylinders. The CFM flow numbers I'm obtaining can be easily converted into massflow if one wanted to analyze any particulars dependent on that converted figure. But for the development phase of the turbo inlet system there really is no need to convert it to massflow. The flowbench provides us with the comparative information needed to develop a better suited system for our higher-power needs. With that said, to answer your question as directly as possible: "what would be the effect of increased airflow and volume to the compressor..." It isn't really a matter of increased airflow TO the compressor per-se. The compressor wheel is creating a low pressure at its inlet which causes the air to move through the pipes into the compressor. As the compressor turns faster and faster, it is producing a greater drop of pressure at its inlet and thus causing more and more of a pressure differential, resulting in a larger quantity of air to move through the inlet pipes. In the stock pipes, at around 5500RPM at 14.5psi of boost pressure, there is ~584CFM of air moving through the inlet pipes. The inlet pipes, as per the flowbench testing, will produce a 1psi pressure drop at this 584CFM of flow. What this means is that in order for the compressor wheel to move that 584CFM of air through the inlet pipes, the compressor wheels have to produce an additional 1psi of pressure differential at their inlets. In order to do this, the compressor wheel has to turn faster than it would if there wasn't a pressure drop through the inlet pipes, or at least, less pressure drop through the inlet pipes. The compressor wheel having to spin faster means it will be producing higher discharge temperatures (less efficient) as well as take a little longer to spool up (since it has to turn faster to make up for the resistance on the inlet side). The effect that improving the flow through the inlet pipes will have on engine VE will be tied directly to the change in efficiency that the compressor wheel is operating at. Since the comp wheel wont have to turn as fast to produce the same target manifold pressure, its discharge temperature will be lower, thus resulting in a higher air density going into the engine. And once again, this shows the irrelevance of the term "VE" - we got more air mass into the engine not by changing the VE of the engine, but rather, the efficiency of the turbo compression system through less pressure drop in the inlet pipe system.
Enthusiasts soon understand each other. --W. Irving.
Are you an enthusiast? If you are out to describe the truth, leave elegance to the
tailor.
Albert Einstein
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