-- [ From: Bob Nogueira * EMC.Ver #2.5.1 ] --
Ulix: I may be getting in way over my head on this topic but I think
where you have gone wrong is in your assumption that the ratio needs to
stay constant. Actually the fuel air ratio needs to change with the RPM
of the engine. I believe it requires a leaner richer leaner mixture as
the RPMS increase ( It may be the other way around). This was one of the
biggest problems of early cars . Miller, of board track and OFFY fame
actually got his start by overcoming the problem with a carb which had
something like eight jets which came in or went out dependent on RPM and
throttle opening. Skinner's genius was in inventing a Carb which
basically flattened the air pressure problem so that only had to deal
with the fuel ratio and air volume. I would liken the problem to
attempting to set the bath water temp by turning both hot and cold knobs
at the same time and neither is linear in its operation with both
faucets having a constantly varying pressures . Skinner's carb basically
set the pressure at one setting and tied the hot and cold knobs together
( sort of like a single lever faucet)
Hey wait a minute,,,,, I may have discovered the SU- plumbing connection
. Gotta hop over to the other thread .
Bob Nogueira
-------- REPLY, Original message follows --------
>snip
>
> > Can somebody explain this to me? I thought the whole purpose of the
> > Constant Velocity carb design was to maintain the mixture at a
certain
> > velocity (to improve low-rpm power), irrespective of the volume of
air
> > being sucked in. At a given altitude, the percentage of oxygen in
the
> > air is (assumed) constant, right? So as RPMs rise, the engine
demands
> > more air, which raises the piston and needle, which enlarges the jet
> > orifice, which permits proportionately more gasoline to flow,
> > maintaining stoichiometry.
> >
> > Now a set of K&N filters will allow more air per unit time to flow,
but
> > they cannot increase the oxygen content of that air (can they?). If
the
> > amount of oxygen is the same as for stock filters, then why do we
need a
> > richer needle? In fact, why manufacture more than one needle per
carb
> > size, since the needle's only purpose is to maintain a
stoichiometric
> > ratio of air & fuel, which ONLY depends upon the sizes of the
respective
> > orifices? At high altitudes, you may raise the jet a bit to
compensate,
> > but the needle profile shouldn't change, should it? Isn't
stoichiometry
> > sacred?
>
> Ulix __/__,__
> .......................................................... (_o____o_).
....
> '67 Sprite
>
>
>
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