Volumetric efficiency

[Enzo Iadevaia]

Hey howard

Where can i take a look at that spreadsheet (turbosize.xls)... Can you post
it or email it to me.. (enzo5555 at yahoo.com)
Thanks






----- Original Message -----
From: "Howard Chu" <hyc at highlandsun.com>
To: <diy_efi at diy-efi.org>
Sent: Friday, October 26, 2001 5:09 PM
Subject: RE: Volumetric efficiency


> > From: "Camden Lindsay" <cjl169 at hotmail.com>
>
> > How does one go about approximating volumetric efficiency at
> > differet rpms?
>
> > I ask because the excellent spreadsheet posted a couple of weeks ago
> > (turbosize.xls) requires it as input, as does the megasquirt fuel
system.
>
> > I (think i) know that the VE of a n/a motor is peaky, whereas a forced
> > induction motor is mutch flatter (??due to less reliance on
> > tuning frequency of intake/exhaust manifolds, tracts, valves, etc??)
>
> > could i use some type of mass meter affixed to the intake of a n/a motor
> > while running and compute VE using the appx air mov't (volume *rpm/2, i
> > think)divided by the output of the meter?  Or is there a simpler
> > way which i am missing?
>
> > Thanks for any help
> > Camden Lindsay
>
> I calculated the VE of my engine using my OBD-II scanner, logging
> MAF/IAT/RPM across the RPM range at WOT. I don't know of any simpler way
> than what you point out. Use the temperature to get air density, and
convert
> mass to volume. Divide this volume by theoretical max volume at the given
> RPM and you have your efficiency at that RPM. To be more precise you
should
> also have your barometric pressure and relative humidity readings factored
> into the air density. All of the formulas required for air density are
> already on the spreadsheet, so it should be simple enough for you to
> generate the required numbers.
>
> As an alternative, if you already have reliable dyno plots of your engine,
> you can approximate the VE curve based on your torque curve. I believe the
> two are directly proportional. In this case, look at your torque peak and
> set the "Mech Eff" fudge factor in the sheet so that the calculated HP and
> torque matches, using an initial guess of VE between 80-100%. A modern
DOHC
> engine design should hit at least 90% at its torque peak, older designs
will
> be less. Once you have this value set, you can work backwards along the
rest
> of your dyno plot to get the VE across the range. The resulting curve will
> be the right shape; it will be directly proportional to your true VE
curve.
> But without a true mass or volume measurement, you have no way to nail it
> down to an actual value.
>   -- Howard Chu
>   Chief Architect, Symas Corp.       Director, Highland Sun
>   http://www.symas.com               http://highlandsun.com/hyc
>
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