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