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  1. #1
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    Boosted Logic - Volumetric Efficiency... (Long)

    For Chromeowner and others that are similarly interested in this topic...

    Volumetric efficiency (Ve) refers to the efficiency with which the engine can move the charge into and out of the cylinders. More correctly, Ve is a ratio (or percentage) of what volume of fuel and air actually enters the cylinder during induction to the actual capacity of the cylinder under static conditions. Therefore, those engines that can create higher induction manifold pressures - above ambient pressure in the case of forced induction engines - will have efficiencies greater than 100%. Volumetric efficiencies can be improved in a number of ways. The most common way is to change the valve sizing or to increase the duration that the valves are open during induction. This is done by modifying the size of the valve openings or by swapping in different camshafts. Another way is by streamlining the ports. Engines with higher volumetric efficiency will lose less power to moving air in and out of the engine. (Adapted from Wikipedia)

    In the case of normally aspirated engines, Ve is typically below 100%. Forced induction motors always exceed 100% Ve.

    The chart and graph below shows the figures for 10 different engines: M70, M73, S70, M60, M62, Steve Cohen's 6.0 Litre, my 850i TT, Dinan Staqe II @10psi, Dinan Stage III @10psi, and the Dinan Stage III @14psi.

    The data used to arrive at the numbers below was painstakingly collected from various sources including dyno graphs from BMW, marketing literature from Dinan, as well as actual engine and chassis dyno graphs.
    .

    .

    .
    Can you see any interesting trends in the graph above?

    Hint: Compare the Ve curves for the normally aspirated and boosted versions of the M70 and S70 motors (Dinan Stage II is an M70 while Dinan Stage III is an S70).

    Rgds...
    - John
    '92 850i Twin Turbo




    ........


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    Re: Boosted Logic - Volumetric Efficiency... (Long)

    John, I'm a little older and my eyes are going but is there info missing..........heh?92 Dinan Stage III TT Laguna green

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    UPDATED - - - Now includes McLaren F1...!!!

    - John
    '92 850i Twin Turbo




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    McLaren F1 Ve now included...

    .

    .

    .
    Rgds...
    - John
    '92 850i Twin Turbo




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    Re: McLaren F1 Ve now included...

    HOLY CRAP...........!!!!92 Dinan Stage III TT Laguna green

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    how can I tell the effect my porting and polishing

    had on my M73? Besides the data avail from the stock version, what woudl I need to obtain to get those numbers for such a graph?

    Dyno, fuel consumption data, acceleration times, etc?

    TIA,

    RM

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    You would need to put the engine on an engine dyno

    ...under the same conditions as a stock version of the engine and then compare the figures between the two.

    To calculate Ve, I would need to know the bore, stroke, # of pistons, and the crank HP at various RPM levels.

    The chart and graph in the post above were derived from a formula I devised whereby I can work backwards from HP to determine Ve.

    Hope this helps...
    - John
    '92 850i Twin Turbo




    ........

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    Here's a clue about why the McLaren flows well



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    48 valves and equal length headers. Oh Yeah...!!!

    - John
    '92 850i Twin Turbo




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    Re F1 efficiency........

    I certainly agree with the 48 valve heads contributing to the high efficiency seen on the graph but up to 4500 rpm it is virtually the same as a stock M60 with 4 valve heads and trailing woefully behind Steve Cohen's at the lower end.
    I do not believe the equal length headers make a significant contribution , although they will help, but I believe the major improvements seen at 4500 rpm and above are from the very short intakes, combined with some very radical cam profiles and Vanos timing, all tuned for that top-end enhancement you see.
    That 100%+ efficiency over around 4500rpm shows the air column ram effect obtained with virtually no induction track resistance, and camshafts timed and tuned with the exhaust to produce a cylinder filled above atmospheric pressure on a normally aspirated engine.
    This is achieved by tuning the exhaust to provide a negative pressure in the exhaust header, (as much as 6-7 psi), combined with a positive pressure in the intake, (1/2 - 1 psi).
    1996 M850CSi


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    How on Earth...

    do they fit that under the hood????

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    Respectfully disagree, Gerry

    An engine usually makes max torque at or very near its highest VE numbers.

    I am very surprised that the F1 engine has as broad a torque curve as it does. It also likely does not end at 6000 RPM!

    Equal length headers are a proven HP increasing tool. Just like intake design, careful exhaust design can and does improve HP and TQ.

    Otherwise we would see iron manifolds on Ferrari V12's, and on Formula 1 cars.

    Greg__________________

    Denton, TX

    1992 850i Laguna Green 6 speed
    1971 Ford Torino GT


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    Does that engine have the same exhaust port

    restriction as the M70/73? or has that been taken care of with the new head?

    BMW E31 Frapper. Check out our Frappr! Jaguar X-Type Frapper. Check out our Frappr!

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    they did not. it sits in a trunk.


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    Re: how can I tell the effect my porting and polishing

    You can take your heads to a good auto machine shop that has a flow bench and someone who knows how to use it.

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    Actually in porting and polishing smoother is not

    better. The reason is boundary layer air flow.

  17. #17
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    The F1's torque curve ends at 7500 RPM redline...

    My spreadsheet only accounts for figures up to 6000 RPM but I temporarily modified it to show up to 7500 RPM's. Sorry, but I didn't want to re-format all of my tables just for one car so the RPM labels aren't showing in the graph below.

    Coolest thing to note is that Torque and Volumetric Efficiency appear to peak at the same RPM.
    .
    Here's the HP/TQ curve for the McLaren F1...
    .

    .
    ...and here's the Ve curve...
    .

    .
    Rgds...
    - John
    '92 850i Twin Turbo




    ........

  18. #18
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    Totally different head design. 4 valves per cyl.

    - John
    '92 850i Twin Turbo




    ........

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    Wow, that is just amazing!

    __________________

    Denton, TX

    1992 850i Laguna Green 6 speed
    1971 Ford Torino GT


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    Have another look. I just updated that post.

    - John
    '92 850i Twin Turbo




    ........

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