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Lynn,
The question was on inlet velocity for a Mazda rotary at 7,500 rpm - if you
happened to have some info on that.
Everyday cars have 450' per sec and race cars 125' per second,( suggested
on a carb site) Ed's calculations used 176' per second which indicated
a bigger inlet diameter. I was thinking about 300 to 350' per second would more
like it, but I have no real hard data!
I indicated the Revmaster didn't have a venturi ( as stated by them), so I
was questioning the strength of the vacuum signal and the impact on fuel flow.
They said that the flat side on the needle created a low pressure area
which sucked-up the fuel and then was sucked in by the vacuum of the engine etc
etc.
George ( down under)
----- Original Message -----
Sent: Saturday, August 18, 2007 2:28
PM
Subject: [FlyRotary] Re: Air/fuel
flow
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)
I have missed the question.
Carbs get leaner near the top of their RPM ranges and use a number of
tricks to maintain a reasonable F/A at high RPM. Even Webers with a huge
number of emulsion tubes and jets for any imagined situation. If you actually
remove the venturi (called the choke) from a carburetor it no longer will
develop any differential pressure, and no fuel will flow through it.
None is way too lean.
More like the Bendix dribble fuel injection that is based on a positive
displacement pump geared to the engine. It just pees fuel all of the time.
Crude but effective.
In many cases of a slide and needle type of carb, the edges of the slide
hole and the flat shelf the slide seals against, is more than enough
turbulence to form the choke. Like Posa, Stromberg, SU and any motorcycle
carb. They all have chokes even though it is not obvious.
A 12A dyno sheet shows 139.6 foot pounds of torque at 6,500 RPM.
and 173.3 HP. This is an engine designed for 9,600 RPM shifting. This has a
Weber carb has two 36MM chokes. Two 40MM chokes would be real nice. Longer
runners would be better, so cruise RPM is also the peak torque or a bit above
peak.
Lynn E. Hanover
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