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.

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.

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.