HEATED MANIFOLDS AND HOT SPOTS
Heat added to the manifold is the probable solution of the present
low-test fuel supplied to the motorist. In the first place you may be
satisfied if your motor runs and does not give any noticeable loss of
power. But the question is, are you getting full power out of your
motor in accordance with the amount of fuel consumed? And are you
getting the proper amount of mileage out of each gallon? The answer to
both questions would probably be in the negative, if both questions
were taken up individually by owners.
[Illustration:
EXHAUST
INTAKE
EXHAUST
GOVERNOR
GOVERNOR
CARBURETOR
Fig. 45. Hot Spot Manifold]
One of the best solutions, if not the best, is the new hot-spot
manifold used on the Liberty engine, which was designed for Army use.
Fig. 45 shows the hot-spot Liberty engine manifold. The intake manifold
is external but short, therefore does not offer much opportunity for
the liquid to condense. From the carburetor it rises up straight to
a point well above the valve ports and the cylinder blocks, and at
the top of the rise it touches the exhaust pipe and divides, the two
branches sweeping downward quite clear of the exhaust manifold to each
block of cylinders. About three inches of the intake passage is exposed
to the exhaust manifold top.
The advantage of this design is that the heating element affects
practically only the liquid fuel and does not have much effect on the
fuel already vaporized. Naturally the liquid fuel is heavier than the
vapor, and as the mixture rushes up the manifold at a high rate of
speed and turns to the right or left, the heavier liquid particles are
thrown straight against the hot-spot, where they are boiled off in
vapor.
Thus, although the total amount of heat supplied to the incoming charge
is small, vaporization is good, since pains have been taken to supply
the heat where it is needed.
[Illustration: Fig. 46. Holley Vapor Manifold--Ford Cars]
Fig. 46 shows the Holley vapor manifold for Ford cars which is
intended to completely vaporize gasoline by applying heat at the
proper point. As will be noted by the arrows, the exhaust gases pass
down, striking a hot-spot at the top of the internal intake passage.
The exhaust gases flow along this passage and finally pass out at the
bottom. The heavier particles of fuel, after leaving the carburetor,
strike against the wall at point (A) and there are broken up by the
exhaust gases. Should any of the globules not be broken up at this
point, they will be vaporized when they strike the hot-spot at (B) as
this is directly in contact with the exhaust gases. It will be noted
that the heavier globules are subjected to a rising temperature.
Starting at (A) and finishing at (B) a control valve regulates the
amount of heat supplied to the intake manifold.