Flow rates

[Tony Foale-3]

Gavin asked:

?? Is their a formula to work out flow rates from square area??

Not really.  It depends on so many factors.  Just to give an idea I achieved
a 40% flow increase at max. valve lift by reconfigurating the inlet port,
the port area was also slightly less with the higher flow port.

Regards

Tony Foale
info@...
www.tonyfoale.com

[Ava Pxia]

In terms of theoretical physics there is a maximum flow through a cross-sectional area based on the properties of the fluid flowing through it, related to viscosity/density of the fluid.  Since flow is neither on a straight line or a steady cross section on an engine it really is far off as a limit to the actual flow.   Most of the formulas you will find will be for steady uniform flow, nothing like the actual thing.
Those pulses of flow of accelerating and decelerating the fluid are changing the density of the fluid in various points.  Right before the inlet when it is shut the velocity turns to zero and then accelerates once it opens.

Koz

--- In mc-engine@..., Tony Foale <tonyfoale@...> wrote:
>
> Gavin asked:
>
> ?? Is their a formula to work out flow rates from square area??
>
> Not really.  It depends on so many factors.  Just to give an idea I achieved
> a 40% flow increase at max. valve lift by reconfigurating the inlet port,

[Jim Schneider-4]

In terms of actual dry air flow testing there are generated real air
flow numbers through a given carb or port.  These numbers are relative
considering the steady state flow of air through the carb opening to
other carbs of differing brand and size and their flow numbers.  This
information has relatively little to do with the constantly changing
movement of air at different rpms and under different conditions in the
entire inlet tract.  It just gives you raw numbers to compare the amount
of dry air flow in a steady state condition going through different
sized and brands of carbs.  If you want more you can get yourself lost
in theoretical physics and flow theory which even the experts aren't
always in agreement on all of the time.  And you can complicate that by
changing the dual carbs to a single carb feeding dual ports with an
unknown adapter manifold and with probably non-steady state flow tested
ports or modeled ports in a computer program that might or might not
take your actual port configuration into consideration.  
 
Your choice, port shapes and the steady state flow through them can be
greatly affected by major changes like Tony made in his cylinder head.
Carbs can be affected by changes in designs like a butterfly throttle
plate, choke plates, round or flat or semi-flat slides or combinations
of slide and butterfly AND choke plates etc.. and on and on to
complicate things so far that the ONLY solution is to bolt your changes
on, tune them to the best of your ability and then compare them either
by seat of the pants difference or on a dyno that might also give you
some variables to fudge your results.  
 
Coz says that in "theoretical physics there is a maximum flow..."  That
is the number that is fairly easy to measure and compare the potential
of the different carbs.  If we go beyond that simple idea, Tony's 40%
flow increase is then meaningless because he didn't test it under "real"
conditions, just steady state flow.
 
Not picking an argument, it was just a simple question asking if there
were formulas for airflow?  Yes, there are formulas for steady state air
flow and they can reflect real world testing generated numbers.  Ports
with bends and shape changes and valves at odd angles affecting port
flow make it a lot more difficult to predict than a straight carb
throat.  
 
Swiss
 
-----Original Message-----
From: mc-engine@... [mailto:mc-engine@...] On
Behalf Of zerogara
Sent: Friday, October 30, 2009 12:51 AM
To: mc-engine@...
Subject: Re: Flow rates


 

In terms of theoretical physics there is a maximum flow through a
cross-sectional area based on the properties of the fluid flowing
through it, related to viscosity/density of the fluid. Since flow is
neither on a straight line or a steady cross section on an engine it
really is far off as a limit to the actual flow. Most of the formulas
you will find will be for steady uniform flow, nothing like the actual
thing.
Those pulses of flow of accelerating and decelerating the fluid are
changing the density of the fluid in various points. Right before the
inlet when it is shut the velocity turns to zero and then accelerates
once it opens.

Koz

--- In mc-engine@yahoogrou <mailto:mc-engine%40yahoogroups.com> ps.com,
Tony Foale <tonyfoale@...> wrote:
>
> Gavin asked:
>
> ?? Is their a formula to work out flow rates from square area??
>
> Not really. It depends on so many factors. Just to give an idea I
achieved
> a 40% flow increase at max. valve lift by reconfigurating the inlet
port,