LP gas now runs a lot of automobiles and trucks

The ability to flip a swicth to LP, if gasoline again runs short, has drawn the attention of almost every driver that hears of the system. Liquefied petroleum gas (LP), in the form of propane, has always been a popular commodity for heating and cooking. Propane has even been used as a fuel for internal-combustion engines almost as many years as gasoline. Now it is experiencing strong surge in popularity.

During the past 12 years almost 3 million LP carburetors have been sold for installation on engines used for trucks, buses, taxicabs, police cars, tractors, and recreation vehicles (RVs).

The future now seems almost unlimited, say many people in the energy business.

Propane is transported and stored as a liquid under moderate pressure. When released, it becomes a clean-burning "dry" gas. It requires none of the additives that usually are blended into gasoline and has a minimum octane rating of 110.

It has no tetraethyl lead or additives and, therefore, leaves no deposits of carbon, gum sulfur, or sludge in the fuel system or engine.

The smooth-burning nature of LP also reduces stress on pistons, rods, and bearings, and results in reduced engine wear.

The low-pollution properties of propane have long been recognized. Research conducted by the US Bureau of Mines indicates that carbon monoxide emission from engines using propane is 50 to 92 percent lower than gasoline-fueled engines and hydrocarbon emissions 38 to 62 percent lower.

A gallon of propane contains about 80 percent of the heat of gasoline. This means that an engine operating on propane delivers fewer miles per gallon than it would on gasoline.

If, for example, you were getting 15 miles per gallon with gasoline, a switch to propane would find you logging 12 m.P.G. and needing 1.25 times as much propane. However, the price of propane is about two-thirds the cost of gasoline. At 15 m.p.g. and with gasoline priced at $1.50, you would save 25 cents every 15 miles with a conversion to propane.

A propane system is basically simple and consists of only four major components:

* An LP fuel-storage tank.

* A filter fuel lock, which removes foreign matter from the liquid propane.

* A converter-regulator, which acts to transfer heat to vaporize the liquid fuel.

* A carburetor which mixes propane and air in proper proportions.

It would be completely inaccurate, however, to give the impression that all one would have to do is buy the conversion parts and install them on any vehicle.

First, an engine in poor condition should never be converted to LP gas. Any defects in the engine, particularly with the valves, will be amplified.

When converting an older engine, a good valve job, tuneup, and oil change should be done. Further, in order to obtain the best results, several engine changes are required. Better yet, start with an engine that is specifically designed for dual-fuel operation.

Since campers have always used propane, and RVs normally have propane tanks for cooking and heating, motor- home manufacturers were the first to recognize the advantages of dual-fuel systems. Optional engines now are offered for conversion by many RV manufacturers.

The engines usually include a few changes for efficient operation, such as:

* High-temperature-resistant valve seats are inserted to increase engine life. This is needed becuase the valves get none of the cooling effect from LP gas that occurs from vaporizing liquid gasoline.

* Higher compression ratios are used to burn the propane more efficiently.

* Ignition timing is changed to realize full engine power.

* The intake manifold is modified to further improve engine performance by eliminating the customary uneven heating.

Dual-fuel systems now are offered by several major RV makers.

Champion, Midas, and Winnebago have announced an LP conversion system for use on van conversions, trucks, and other vehicles. All three conversion systems allow dual-fuel operation by using a switch mounted on the dash.

If you want more information on dual-fuel systems and where they can be ordered, write: Champion Home Builders Company 5573 East North Street Dryden, Mich. 48428 Foretravel, Inc. 1221 Northwest Stallings Drive Nacogdoches, Texas 75961 Midas International Corporation 55667 Country Road 15 South Elkhart, Ind. 46514 Winnebago Industries PO Box 152 Forest City, Iowa 50436

A dual-fuel system utilizing propane seems like a good move for the RV camper but is it a practical idea for the automobile user.

For one thing, propane is plentiful. Even though its price and supply are regulated by the Department of Energy, it is not included in any present standby fuel-rationing plan. It burns very clean and could be considered an environmentalists' dream fuel.

The price also promises to remain appreciably less than gasoline; that is, unless everyone decides to switch.

Should a large number of car owners opt to go to conversion shops, demand for the fuel could exceed the ability of stations to supply it. This is highly unlikely, however.

If an LP system is economically impractical for your present car because of age, a dual-fuel engine could be considered when you buy your next new car.