The L-Head motor, or what is more commonly known as a Flathead, was the mainstay of most auto manufacturers before World War II. A flathead motor is just that - the head is a flat, cast piece of iron that is bolted down on top of the block. The valves and the entire valve train are in the block itself. The head is relieved to allow for compression and for valve clearance, but it contains no moving parts (except the thermostat). The head is partially hollow to allow coolant to pass through to assist in cooling the engine.
Virtually all early cars were flatheads, and the flathead stuck around for a long time, but few if any flathead motors had the staying power of the Chrysler Corporation's flathead 6. As late as the early 60s (I have heard 1963), this engine was being produced for industrial uses such as stationary pumps, arc welders, forklifts, and farm equipment such as harvesters and combines. Because of this, parts are still available on the shelves of better auto parts stores. I have purchased water pumps, fuel pumps, and tune up parts off the shelf for my '48.
The flathead, because of its design limitations, was destined for doom as the fabulous fifties began to roar. The public's desire for more power prompted Chrysler to produce the legendary Hemi in 1951. Chrysler was so proud of its new engine that the front of the hood of the V8 equipped cars had a large chrome 'V' to identify the engine to all the world. The Hemi powered Chrysler 300 in 1956 was the most powerful and fastest production car in America that year, averaging 139.9 mph at Daytona.
Chrysler - 1954 - 264.5 cid
DeSoto - 1954 - 250.6 cid
Dodge - 1959 - 230 cid
Dodge Truck - 1968 - 250.6 cid*
Plymouth - 1957 - 230.2 cid
* Richard Davis wrote: The 251-3 standard engine used in the 1961-68 WM300 Power Wagon? It had replaceable hardened exhaust valve seats, full flow filtering, and full pressure oiling. It had 115 net hp at 7:1 compression until 1966, and in 1967-68 it had 125 net hp at 8:1 compression.
What made the flathead so versatile was its dependability and torque. The largest flathead six Chrysler used in its automobiles was 265.5 cubic inches that produced 218 ft/lbs of torque at 1600 RPM. So, at just off idle, this engine produced maximum torque, making it ideal for the applications above.
In comparison, the last flathead 8 was used in 1950, with 323.5 cid and 270ft/lbs @ 1600 rpm. Although the 8 was more powerful, most people found the smooth power produced by the six was sufficient, and so a vast majority of older Chryslers found today are equipped with sixes.
These figures are at the rated compression of between 7 and 7.5 to 1.
The flathead six in my 1948 Chrysler Windsor Club Coupe is a smooth, powerful, efficient powerplant. On the highway it regularly gets from 17-19 mpg at average speeds of near 60 mph. Not bad for a car that weighs over 3600 lb (shipping weight was stated as 3463 lb)! That 'little' six is capable of speeds in excess of 100 mph (I've had it up to 95)!