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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 was talking about the staight RPM lines plotted over the chart (added by Tektrader) not the efficency islands. I guess I should have made myself more clear.
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.
I've haven't attempted to make anything in MS Paint. A better understanding how to read these charts with engines of wildly varying flow would be very helpful in picking out what turbo application to chose for your engine. Instead of simply basing it on 1.5l of displacement (how most have been reading these charts) but also taking into account how a really great breathing engine will effect how efficiently you will be using a given turbo at a given RPM (basically help people with varying amount of port/flow work better understand how that increase in Flow/VE will shift where in their turbos efficiency range they will be operating. I never said anything about tuning my car based off a compressor flow map.
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?
If one is more restrictive they can be flowing the same CFM because as the more restrictive one would me more pressurized.
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.
I think you mean the engine with the LOWER VE will comsume(if by consume you mean restrict) more CFM/rpm. If by comsume you mean flow, then an I agree. I also agree with everything else after the first sentece. Do you agree with my point that an engine with a HIGHER VE will have lower EGTs at the same power level?
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.
I agree that "boost" is not the right way to think and go into that HERE The basic points I am making above are still valid though, whether or not they are the ideal way to think about it. Again, we are on the same page here as well.
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.
Agreed, but higher VE != higher EGT as you insinuate with the above statement
"Higher VE = higher CFMs = higher EGTs = higher turbine speed.
This is pretty basic theory, isn't it?" Timing, A/F being equal the EGT will be lower at the same power level with a higher VE engine. I hope my point isn't buried in what you consider "arguing the semantics of the problem". Am I getting to "the fundamental truth of the matter"? Or has my "anal retentive nose-picking has brought the discussion to a new level of abstract inconsequentiality"?
m a g l i t o
parts are FINALLY here - engine is going back together NOW
sig photo by me effects by ZXRider(SoCal)click here for latest build update post
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