MOTOB VEHICLE 329 MOTOR VEHICLE can, as a rule, be easily and quickly started; the fuel is univex'sally obtain- able, and the cruising radius is large. The drawbacks for this type of motor are that the motor has a limited speed range at which it may be operated and is non- reversible, consequently gearing in the transmission is necessary. Because of the great heat generated by the explo- TOURING CAR sion of gases some cooling system is needed, and the motor must be made to undergo a complete cycle of operation by some external mechanical means be- fore it can be made to start. The early motors used in motor vehicles were single-cylindered or at most had two cylinders, cast singly. The modern range of cylinders is from four to twelve. The four-cylinder car, in which the cylinders are vertical and cast en bloc is extensively used for inexpensive cars which are produced in great quantities. The six-cylinder motor, in which there is a continuous torque, is extremely popular, and of recent years multi- cylinder motors, with eight or twelve cylinders each, have been used with great success particularly for high-grade cars. In the multicylinder type of motor, the cylinders are usually arranged in two blocks of four or six cylinders each, which operate on a common crank shaft. The question of the proper angle between LIMOUSINE the line of action of the two cylinders is much debated — some engineers use 90 degrees, other designers use 60 degrees, and some as low as 45 degrees, though 90 degrees and 60 degrees are the most common. The standard type of motor has poppet or lifting valves, and the motor may be L or T head, or, as is frequently the case in modern design, the valves are locate(^ in the head of the motor. Some types of modern motors have four valves to the cylinder — two intake and two exhaust valves. One manufacturer of a high- frade car claims that a sixteen-valre our-cylinder motor has all the advan- tages and none of the drawbacks of the multicycle motor. Sleeve and cylindrical valve motors are advanced by some designers, and are used with varying degrees of success. The sliding parts of a sleeve-valve motor have to be thor- oughly lubricated, and the excess oil fre- quently causes the motor to smoke. In cold weather the oil is likely to congeal, making starting difficult. The early cars carried their fuel in tanks which were usually located under the driver's seat, the gasoline flowing to the carburetor by gravity. The incon- venience caused the passengers when fuel was replenished caused some design- ers to move the tank to the dash, but this did not produce sightly lines. With the gravity system it is necessary to CABRIOLET place the carburetor low on the motor, and on hills the feed was sometimes interrupted. The next change was to locate the fuel tank at the rear of the frame, and the gasoline was forced to the motor under pressure, supplied either by hand pump, or from the exhaust, or both. Modern design uses a small vacuum tank, which draws gasoline to a reservoir located above the motor, from which it flows to the carburetor by grav- ity- . . The liquid fuel is mixed with air m the carburetor to form a vapor. Engines are now striving to perfect methods to counteract the increasing sluggishness. The carburetor is often heated by exhaust gases or by water jacketing. Hot spots caused by exhaust gases or electrically heated wire gauze are placed in the in- take manifold to break up and preheat the gas before it goes into the cylinder. When the gas reaches the cylinder it goes through the four cycles of intake compression, explosion, and rapid expan- sion and exhaust. The noise of the ex-
