This engine was, with only slight differences used through 1936. They had poured babbitt main bearings and inserted rod bearings, they had 221 Cu In and were rated at 85 HP. They were arguably painted Ford engine green, a std hue carried over from the Model A era. (there is still a lot of controversey about this point)
In 1936 Ford brought out an improved model of the original engine that still had 21 head studs, water pumps on the heads, like the '32-'35's, but used insert main bearings that eliminated the babbit mains used previously, there is a a designation for these engines, that I have forgotten, L?, I believe.
In 1937 a unique 85 HP engine was used that had 21 head studs, full insert bearings, but the block was changed to accept water pumps, whereas formerly the water pumps had been in the heads. The hose necks were moved to the center of each head, and the bottom hoses attached directly to the new model water pumps.
In 1938, there were a number of significant changes, a new block was used that had 24 head studs on each side, it still had 3 1/16 bore and 3 3/4 stroke. The crankshaft journals were 2.5 in. on the mains, 2 in on the rods.
In 1939, the 24 stud 221 CI engine was continued in the Ford cars and trucks, at the same time a new engine was developed for large trucks. it was known as the 81T, and had a bore of 3 3/16 and a stroke of 3 3/4 and 239 CI. it was rated at 100 HP. When the new Mercury line was introduced that year, it used the 81T engine, but they changed the designation to 99A, but they are basically the same engine. internally the connecting rod journals were increased in diameter to 2.139 in.
These 2 engines were the standard "big " V8's of the late prewar period, the V8 60HP was introduced in 1937, modified in 1940, and discontinued in '41, when the flathead 6 cyl was brought out.
The 4 cyl 9N Ford tractor engine was also available in cars and trucks on special orders. This engine produced 40 HP and was known as a "half a Merc" because it's bore and stroke were 3 3/16 X 3 3/4 with just 4 cylinders. It was the logical replacement for the now obsolete Model A and B 4 cylinder engine used from 1928-33, and preferred by a segment of Ford buyers.
Things went on hold during the WW2 era, and in 1946 the famous 59A engine became standard until 1948 in both the Ford and Mercury cars, in the trucks through 1947. It was the same dimensions as the 81T and 99A, 239 CI, 100 HP, and became the hot rod motor of choice for some time. Most aftermarket postwar speed equipment was made for the 59A engine, and it acquired the popular name "'48 Merc flathead".
In the 1948 model year, Ford brought out a re-styled truck line before the revamped 1949 model year cars. The standard V8 engine in these trucks was known as the 8RT engine, and closely resembled the 8BA new style engine with detachable bell housing and upright conventional distributor. The 8RT engines are preferred by some enthusiasts because it had hardened valve seats and more "meat" in the cylinder walls so they could accept a larger bore.
In 1949, the re-designed engine known as the 8BA appeared in the cars, the 8RT was used in trucks, bore and stroke remained the same, water necks and pumps were changed, the bell housing became detachable, and these remained the basic Ford engines until 1953.
There was also a very large flathead V8 used in very large trucks known as the 8EQ. These were the 337 CI '49-'51 Lincoln engine, transformed to be used in trucks. These changed to overhead valves in 1952
In 1949 the stroke was increased in the Mercury to 4", giving it 256 CI and 125 HP. This also was basically unchanged until 1953, these engines were known as 8CM's and the 4" crankshafts could be used in the 59A blocks, and if ground off center could be "stroked" an 1/8 to become a 4 /1/8 stroke, or 3/8 more than stock 59A, and when the bore was increased 3/16 to 3 3/8, this popular hotrod term of 3/8 X 3/8 was adopted, these engines had 296 ci, and were capable of developing up to 300 HP.
There are a lot of other changes and divergences that I either do not know, or have skipped over, so be tolerant, however this does give, I believe a reasonably accurate overview of the subject.
submitted by Rolf Burdette