Randy Rees (Volt Computer) wrote:
> Why would polishing use more fuel, you would think that if the mixture
> flowed better and you did not loose some in the "pockets" you would have
> better fuel metering and actually get better mileage.
With our LBCs and their sophisticated fuel systems, you don't want the air
flow too smooth because all the gas will fall out.
Seriously. On the "new and imporved" fuel injected engines, they are messing
around with the intakes for smoother flow, better torque, etc., because they
are 'dry' -- no fuel in the air until right above the intake valve (the
pocket). You need only be concerned with smooth and efficient air flow.
With our old engines, some amount of turbulence is good to keep the gas
suspended in the air flow. Imagine the fuel charge rolling down the intakes
like a tumbleweed. That is a good thing -- to a point -- to keep the mixture
mixed.
As Mr. Eastman chisled into his tablet, the easiest gains for polishing is
right above the intake valve. There is no worry about gas "falling out" as
it is done traveling so the smoother it is in this area the better. Most of
that gains, again, are around the valve guide and the "short radius"
(bottom) of the turn past the valve into the cylinder.
Porting to a high sheen can make the air flow "stick" to the walls of a
pipe. So the "short side" polishing helps the charge make the turn into the
motor. Gasket matching is still a good idea but high gloss ain't a goal.
Now who is going to be the first to tell the horror story on rubber-bumper
Midgets? There the intake manifold and the intake ports on the head are way
different sizes as if the manufacturer didn't care how the motor performed.
On Midget's with 'A' series motors, there are two steel rings to line up the
intake manifold to the head. Some hot rodders 'port' the intakes by
grounding down the metal in the intakes to a depth of the rings (and, thus,
not use them).
And to answer the original quesion, on a higly-ported carbuerated engine,
you may very well need more gas to counteract the fuel falling out of
suspension. Of course the "falling out" is temporary -- the puddles of fuel
on the floor of the intake will be ingested in one big gulp which will be a
big stumble until the motor "clears its throat" and takes off.
--
Bob Allen, Kansas City, '69CGT, '75TR6, '61Elva(?)
"Heard the exahust howl of a restored XKE at 100 mph? Neither has anyone
else."
|