Ed,
I would like to clarify another
point and that is your velocity figure of 120 mph.
I will explain:-
I have studied carb sites for
snippets of information ( they don't give much away), however one
did say that carb choke speeds are usually 450' per
second and racing cars 125' per second.
I assume the racing car inlet speeds
are lower because the throttle is wide open with massive sized
inlets, therefore lower vacuum signal.
Your calculations use 176' per
second. Can you clarify where you acquired that figure from as a
higher figure would reduce the inlet area
calculations.
The carb I am looking at is the
Revmaster, they currently only have 40mm carbs available due to
slow demand of the 42/44mm. One good thing is that the carb
operates without a need of venturi, however the vacuum
signal must be weaker ( because of this)coupled with a weaker
signal because of the shape of the rotor face.
At the very least the lack of venturi
also eliminates the choke potential. Some carbs have a 44mm inlet
but are choked to 36mm which would increase inlet speed (good),
but as you say, may move into the choke restriction area
(bad).
A weaker signal would also effect the
idle mixture as this is driven by vacuum rather than air flow,
however I guess this can be adjusted manually. Should be plenty of
vacuum at idle with the slide closed.
I have asked Revmaster for air flow
and velocity figures, but these may be derived from piston engine
type figures.
If you or Lynn could comment on this
it would be greatly appreciated.
Also my research indicates that flow
air/ fuel mix richens at higher RPM and altitude. I can't
remember why at higher RPM - mind block, however for altitude it
is because fuel flow is driven by air flow and even
though the density of the air is lower ( at altitude) the flow
remains the same - therefore richer mixture. Revmaster says their
needle design is self leaning ( to a degree) because of design.
I assume because the air density directly affects the suction
to the rear side of the flat ground needle, ( this provides the
low pressure area rather than the venturi) therefore with
reduced density you have reduced suction and reduced fuel and
leaner mixture. However I will clarify that when next we
talk.
I find this all very
interesting!
George ( down under)
Well I'll be Ed,
2.4137sq" = (.877x.877xPi = 2.416),
therefore .877 Radius or 1.754 Dia or 44.55 mm for the carb
opening.
I'm working on the rest!
George ( down under)
For inlet, you take the CFM and you need one
other factor - what velocity do you want through your inlet?
Lets say you want a higher velocity of around 176 feet/sec (120
MPH) then we know that Volume = Area * length. If were
want 176 feet/sec velocity from 176 CFM air flow then coverting
CFM to cubic feet per second were have 176Ft^3/min / 60
Second/Minute = 29.333 Ft^3/
Second