Throughout the 1930’s, racecars powered with Ford Model A and Model B engines were the crowd-pleasing underdogs in big car racing. The Fords would easily out-accelerate the competition of expensive pure bred (Miller and Offenhauser) equipped cars at the beginning of the race and also coming out of the corners in oval track racing, however they would often break before the end of the race. Aftermarket heads were available to fit any budget and included flathead, F head, I head, SOHC, and DOHC configurations. They were normally aspirated, and the more potent Fords with compression ratios exceeding 12:1 could produce over 250 HP from 200 in*3. Tetra-ethyl lead and other chemicals were readily available and freely added to fuel to boost performance. HAL heads and others were cross flow and featured hemispherical combustion chambers long before Chrysler introduced its’ famous hemi in 1951. The 1930’s were an era of creativity where good mechanics would often beat engineers in discovering how to obtain greater power from engines. Fronty even made a DOHC configuration that was called a "stagger valve" which featured four valves per cylinder, where diagonally opposite valves were either intake or exhaust. This configuration required intake and exhaust manifolds on both sides of the cylinder head.
The Fords were fast off the line and out of the corner because their bottom end (connecting rods and crankshaft) was extremely light (low inertia) and strong. However, they were also extremely fragile because that same light bottom end construction could not sustain high loads for any length of time. It was common to install a new crankshaft after a few races to avoid breakage. Crankshaft deflections and stresses were excessive and far exceeded modern engineering limits regarding fatigue. The fatigue properties of materials were not well understood. Towards the end of the 1930’s, many of the same manufacturers that originally supplied the more potent overhead valve conversions also supplied 5 main bearing crankshafts with counterweights and matching new cylinder blocks to increase reliability (HAL, Dryer, Cragar). Model A and B based engines were expensive to maintain but were dominant (at least in numbers) in big car racing until WW2.
After WW2, racing took a new direction. Veterans returning from the war came home with fresh ideas and a desire to participate in racing instead of just being spectators. The interest and participation in midgets, drag racers, and jalopies exploded. Ford flathead V8’s became dominant due to a variety of reasons including engineered counterweights, pressure lubrication, stiffer crankshaft, insert bearings, economical to maintain (no need to change crankshafts to avoid fatigue failures), and the huge variety of inexpensive aftermarket speed equipment that was available.