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