| It is my understanding those lines were made simply using the engine volumetric flow or EVF on the page you listed. They do not take into account the following variables (listed in order of my understading of their importance). VE (or for simplicity say we will say how well the entire system flows).
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Temerature (ambient)
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pressure (ambient) - more dependent on alt. So, MY goal is to figure out how to try and take into account how those varibles effect those plotted lines (transform them to something useable to me). They shouldn't have any effect on the plotted lines of the islands. As ambient temperature increases, the engine RPM lines should shift to the right. As ambient pressure increases, the engine RPM lines should shift to the left. I'm not sure how this would be usable to you either way, your VE isn't going to be the same as anything you have drawn in microsoft paint. When it comes down to it, you tune for your specific vehicle, not a pressure chart, although that could give you some clues on how much boost you should limit yourself to, to keep from overspinning your turbos. Hopefully Kenny or someone else who seems to better understands this will jump in on this. My understanding is the heat that is generated on the intake comes from two things.
1. physical heat generated by the turbo (spinning fast -friction), and heat soak from the VERY hot gasses powering the turbine side.
2. the act of compressing air (basic thermodynamics) Your statement about a higher VE causing higher EGTs I think doesn't take into account point 2. A better flowing engine (higher VE) will have LESS manifold pressure (boost) at a given power level vs. one with poorer flow. So, if the turbine/compressor wheels are spinning at the same speed on a car with 70% VE and one with 90% VE the one with 90% VE should be building less boost (less resistance to flow) but flowing the same amount of air and since that air is less compressed it should be cooler (lower EGTs). Why would the VEs be different if the respective engines flowed the same CFMs? They wouldn't. Again, how could they possibly flow the same CFMs and have different levels of boost? The engine with the higher VE will consume more CFM/rpm than the engine with the lower VE. Yes, the engine with the lower VE will have higher intake temps. The higher VE engine would allow more airflow into the combustion chamber, which would in turn require more fuel, which would in turn result in a more powerful explosion and higher EGTs despite a small intake temperature differential. Now, the car with higher VE the turbine/compressor should spin up faster (it doesn't have to work as hard) but boost should build slower (since there is less resistance to flow). But, power should build quicker on the higher VE engine even though boost is lower because the intake charge is cooler with the same amount of air flowing. Please stop thinking in terms of "boost," it's on oversimplification of PV=nRT. Think CFMs (n=PV/RT, the actual number of air molecules), the actual amount of air flowing through the engine. You keep saying the power is higher even though the "boost" is lower. Yes, the pressure is lower, but that doesn't mean the total number of oxygen molecules is lower. So, I think your statement about higher EGT due to higher intake temps on better flowing (higher VE engines) is flawed. Also, my understanding is the choke like (not the surge line) is what holds these turbos back on the top end of thier power output. Well, he's right about the EGTs being relatively higher per RPM, just not for the right reason. The EGTs will be higher, but not because the intake temps are higher. The EGT will be higher because the total number of oxygen molecules in the higher VE engine will be higher, thus using more fuel and causing a more powerful combustion. The intake temps will not necessarily be higher because the pressure will be relatively lower compared to the lower VE engine, despite higher CFMs. The increased turbine speed could indeed make the intake temps higher, but the VE is a mitigating factor, it's possible but not necessary. I realize I could be misundstanding this or be confused and would love to have more input on this to better my understanding. Thanks in advance guys!
Recursively Yours,
Kenny...
PETZ Member #5
SteamyZ. Never had did me wrong. - SL103 07/06/04 11:58:15
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