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Thread: Understanding what Jeff Lucius (Stealth316) Means by "Modified Engine"

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    Understanding what Jeff Lucius (Stealth316) Means by "Modified Engine"

    I was going over Jeff Lucius's article on Turbocharger Compressor Flow Maps again and I want to understand what his usage of the term "modified engine" actually entails when he's discussing and displaying compressor map images with engine demand lines.

    He never really clarifies exactly what "modified engine" means, or what modifications are included in the term.

    Does this term only refer to modified heads and/or pistons. What modifications can one do in order to manipulate the placement of demand lines?

    I could guess at what he means but I would rather know that I'm correct in my assumptions.

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    Forum User Feedback Score 1 (100%) lawdogg's Avatar
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    It refers to any modifications at all that effect the engine's VE vs. RPM relationship. AdamVR4 / i3igpete / anyone who tunes based on VE (I don't think AEM's maps are VE based are they?) would probably be resident authority on that.

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    Banned Feedback Score 11 (100%) J. Fast's Avatar
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    Quote Originally Posted by steve68 View Post
    It would have been more useful if the graphs had been plotted for an unmodified car.
    VE for an unmodified car is only about 60% at 7000.
    Any mods to cams or heads usually increase VE.
    Max VE isn't 100%, it's over that allowing for ram effect and combustion chamber volume. For an 11 to 1 motor it's 110%. more still for 8 to 1.

    Steve
    There are several interpretations on V.E. The correct interpretation says the percent of residual from the intake vs. exhaust stroke in the cylinder chamber. Understanding the true definition of V.E. you should never be able to exceeed 100% otherwise you would have a perpetual motion machine.

    Jeremy

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    Forum User Feedback Score 1 (100%) lawdogg's Avatar
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    VE means volumetric efficiency. It is not based on mass and there is no way to exceed 100% VE.

    If you have a 1 gallon jug, it does not matter how much stuff you can pack into it, it will always remain 1 gallon.

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    Good responses

    I figured that changing the factors in the heads and modifying bore/displacement would obviously modify the VE but what I'm particularly interested in is how much having a more efficient intercooler and a more free flowing exhaust will affect VE. Also, and while I doubt it has an affect, does modifying fuel help increase VE under certain conditions.

    After having read a few more articles, Jeff does make the statements that VE is affected by more efficient intercoolers and more free flowing exhaust but doesn't state to what degree those modifications make a difference. I don't even know if it's something that one can easily know anyway.

    Those postulations stated, I did read further into and through Jeffs articles so while I do understand VE more than I did when I made the post, I'm still curious to know some of the less obvious ways to increase VE.

    Edit: I'm mostly interested in this from a highly technical perspective so feel free to not dumb down any responses

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    Banned Feedback Score 11 (100%) J. Fast's Avatar
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    Quote Originally Posted by lawdogg View Post
    VE means volumetric efficiency. It is not based on mass and there is no way to exceed 100% VE.

    If you have a 1 gallon jug, it does not matter how much stuff you can pack into it, it will always remain 1 gallon.
    Yup, that's pretty much it. The actual volume flow of the engine will not change (unless you punch a hole in your cylinder wall or frag a piston ). Since we can not phsically change the size of our cylinder while it's running, then we can only move exactly the same volume through it in any cycle which would be considered 100%VE.

    When using forced induction we're simply making the same volume of air more dense. Put one cup in the combustion chamber filled with whatever you want, and then pull the same cup out after an engine cycle. Unless you work for NASA you'll generally end up with less volume in the cup .

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    Engineering Nerd verified Feedback Score 0 Tiberius's Avatar
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    The TARDIS has more than 100% VE :-D

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    Quote Originally Posted by steve68 View Post
    A 3 litre motor has a swept volume of 3 litres every 2 revolutions.
    What it also has is the volume of the combustion chambers. They are NOT part of the 3 litres.
    A VE of 100% will be the equivalent of 3 litres of air at atmospheric temp and pressure sucked into the motor every 2 revolutions. This does not take into account of the combustion chamber volume. Therefore 100% VE CAN be exceeded, that's because it's not a 1 gallon jug, it's got a domed lid on top.
    Anyway there's heaps of mistakes in that article but you'll have to read it to figure them out.
    That's what happens when you rely on computers and cut & paste.

    Steve
    Nope, that is an incorrect assumption aswell. You're saying that the shape of the piston, the quench pad, and conical sections of the valves are not included in the math? It's the entire volume of the 6 combustion chambers (no matter what their shape). The greater efficiency comes from how the intake vortex is introduced into the clylinder and how it exits which means it's swept more efficiently. If you are exceeding 100% how many laws of thermodynamics are you violating and what's the point of even measuring efficiency?

    Jeremy

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    Eight factors that affect V.E.

    1. Fuel type, fuel to air ratio, fraction of fuel vaporized in the intake system and fuel heat of vaporization

    2. Mixture temperature as influenced by heat transfer

    3. Compression ratio

    4. Intake and exhaust manifolds design

    5. Intake and exhaust ports design

    6. Intake and exhaust valves geometry, size, lift and timings

    7. Ratio of exhaust to inlet manifold pressure

    8. Engine speed

    Here's a fantastic article to read that may help some people understand how to evaluate VE. http://docs.google.com/viewer?a=v&q=...Mial3k0fbIPYzw

    Jeremy

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    Excellent, thats the type of list that I'm interested in and that master thesis is precisely what I was looking for.

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