[Diy_efi] : tuned port manifolds

[Dave Williams]

Jesse Ruppel wrote:

>  We used "Design of Machinery" by Robert L. Norton in the mechanisms class I
> just finished up taking.  It has a quite complete chapter on cam design in
> general, and even though there is little said on implementation to engines,
> it is still required material to design a proper cam.  For the class I wrote
> up a rather lengthy Matlab program that will let me design a cam to meet any
> position, velocity, acceleration, or jerk requirements.

 You need the standard reference: "Valvetrain Design" by Michael C.
Turkish, 1946, printed by Eaton Corporation.  There's also some useful
stuff in the NACA papers, at naca.larc.nasa.gov.


 
>   I'm trying to design a turbo header for my Supra right now too.  I've been
> looking for an in-depth (grad or PhD level) text on exhaust manifold design
> and I haven't been able to come up with much.  Right now I am working on
> modeling the flow through the header using the differential equations
> Heywood presents in "Internal Combustion Engine Fundamentals" but solving

 The key is to watch the cylinder pressure through the exhaust cycle. 
Most of the exhaust mass passes the exhaust valve before the valve is
fully open, as choked or sonic flow.  Depending on the engine geometry,
the residual pressure may range from an average of 100 PSI to below
atmospheric at times.  You're not going to see below atmospheric unless
the exhaust is unmuffled or has an enormous receiver volume.

 Since the majority of the gas flow past the valve is sonic, the 'slug'
can be treated as an incompressible fluid without throwing things off
too badly.  For a six cylinder there is no interference between
cylinders as long as the cam timing is below 240 degrees, so it really
doesn't matter what you do with the pipe diameters or lengths.

 You can get diverted into all sorts of acoustic resonance dead ends,
but they're just mind candy.  Resonance in the exhaust system reflects
through the cylinder all the way through the intake tract to the air
filter.  Carburetors and some MAF EFI systems were very sensitive to
this, but twiddling with the exhaust geometry was just playing with
secondary effects.  As long as your fuel metering system isn't bothered
by exhaust resonance during overlap, and there's no interference between
cylinders on the exhaust strokes, and back pressure isn't too high (less
than, say, 10 PSI at WOT), you don't have to worry much about the
header.

 You will, again, find considerable information of this type among the
NACA papers, which have been scanned and are kept on the Web by the US
government.
These are all primary research documents, written by people paid to do
hands-on test-to-destruction, not tertiary or quaternary summations like
Heywood.

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