Date: Sun, 31 Jan 1999 16:14:24 -0800
From: Paul <rotaryeng@earthlink.net>
To: z <rotaryeng@earthlink.net>
Subject: Dynamic Chamber Intake manifolds
Tracy Crook wrote:
Paul Yaw wrote:
That is way off base. Velocity is determined by the rate of change
of
volume of the working chamber, and inlet cross sectional areas.
The
side port motors make less power because they don't flow nearly as
well,
and unless thay are bridge ported, they have almost no overlap.
This
theory illustrates a VERY poor understanding of flow dynamics.
Read your own responce carefully to see my point. As you said,
Velocity is
determined by the volume and cross sectional area of the runners.
Since we
are feeding the same volume with BOTH runners, the cross sectional
area of
the runners must be ADDED. For a given sized runner, velocity is cut
in
half when you go from 1 runner (peripheral port) to 2 runners (side
port).
This is one of the reasons the side port engine flows so much less
than the
peripheral port. I wish you had addressed the fundamental question
in the
previous message. Is velocity important or not? If it is important,
the
understanding was right on. If you think it is not important, let's
hear
the arguments for why not.
I'm starting to repeat myself on the issue of peripheral Vs side port
but
I'll say it once more. In the real world of actually flying these
things,
we of limited time and financial resources are going to use the side
port
engine. There is nothing to be gained by comparing peripheral ported
Le
Mans racing engines and stock or street ported side port engines.
But, for
the sake of pure achedemic argument, do the math and figure out the
relative
cross sectional areas of two 1.5" dia. runners Vs one 2" runner. Oh
hell,
I'm so worked up I'll do it. The 2" 'sewer pipe' has LESS area than
two
1.5" runners. (3.14159 Vs 3.534 sq. inches) IMHO, The two inch
runners
(on the Le Mans engine) are not sewer pipes but a carefully chosen
dimension
to optomize velocity and of course match the throttle body size (keep
the
cross section the same).
Tracy Crook rws@altavista.net
Paul Lamar wrote:
Use two tapered intake pipes near the ports and make them bigger.
Paul Lamar
Tapering the pipes will cause them to resonate at a higher
frequency. I
found this stated in literature years ago, and thought it seemed
impossible, so I did some testing and found this to be true.
Paul Yaw
Raising the resonant frequency is the last thing we want to do. I
assume
that was your point. My understanding of intake manifold runners at
this
point, is that cross sectional area should be as constant as possible.
Not
an expert here. Is that true?
Tracy Crook rws@altavista.net