There are three main schools of thought about Henry Ford’s flat head V8 engines; one holds that this engine was an unqualified and brilliant achievement in design and engineering, while another maintains that this particular engine was inherently unreliable and uneconomical to operate, and should therefore not have been allowed to see the light of day. The middle ground is populated by many proponents of this engine, who believe that while the first iterations of Ford’s flat head V8 were less than perfect, this engine was perfect for its time when it was introduced in 1932. In this article, we will take a closer look at what made Ford’s flat head V8’s so successful, as well as what caused its demise in 1953/54, starting with this question-
Consider the image above- it shows a flat head V8 engine’s cylinder block, in which the valve ports were incorporated into the block, as shown by the row of holes above the cylinder bores. Since the cylinder heads did not contain the valves, the cylinder heads were basically flat metal castings, into which the combustion chambers were machined. The cylinder heads also incorporated pathways that allowed the air/fuel mixture to enter the cylinders, and the exhaust gas to exit the cylinders.
The camshaft was located in the block between the two banks of cylinders as indicated by the arrow. While this arrangement worked well enough (as it still does on many modern V-type engines), the location of the valves in this engine design was at same time the flat head engines’ greatest drawback, the details of which we will discuss in some depth later on. Nonetheless, the term “flat head”, derived from the overall flat appearance of the cylinder heads.
In technical terms, the closest modern analogy to Ford’s flat head engines is the basic design of small stationary four-stroke engines such as those used on lawn mowers and small power generators, in which the engine valves are also incorporated into the engine block, which brings us to the question of-
Limited space precludes a comprehensive discussion on the history of V8 engines, but it must be stated that Henry Ford did not invent the V8 configuration. In fact, a fuel injected OHV V8 engine was built and patented by Léon Levavasseur as long ago as 1902, and some early versions of these engines saw service in aircraft of the time.
Moreover, when Henry Ford started development of his flat head V8 there were already a slew of operational V8 engines is use by various manufacturers, but none of these engines were available in commercially viable numbers. The main reason for this was the fact that existing V8 engines were made up of several castings, all of which had to be bolted together to produce a complete engine. In practical terms, this made the V8 engines of the time too expensive to produce in large volumes, meaning that only wealthy customers could afford them.
Henry Ford was nothing if not a practical man, and although he was not a trained engineer, he saw the possibility of casting an engine in one piece, thus eliminating the time consuming and expensive finishing processes other manufacturers had to complete to produce a working engine. This was however only one-half of his motivation to mass-produce a cheap V8 engine - the other half involved his massive ego that drove him to compete with, and outdo the trained engineers at other manufacturers.
These aspects of the development of Ford’s flat head V8 fall outside the scope of this article, but suffice to say that it was only because of a), Henry Ford’s iron grip on all aspects of the company’s management, and b), his desire to be the saviour of the motoring public that the development of this engine did not bankrupt his company.
However, despite Henry Ford’s desire to have it otherwise, casting techniques were rather primitive at the time, and almost all the engine castings produced during the first year of production had to be scrapped because of inaccurate core placement to produce the cylinder bores. In time however, Ford engineers devised a technique to prevent the cylinder cores from moving during casting, with the result that Ford could now produce one-piece engine castings in very large numbers.
This achievement was without any doubt Henry Ford’s greatest contribution to automotive engineering, and by 1932, Ford managed to produce cheap but working engines in large numbers, the first iteration of which was fitted to Model 18 Fords in 1932. The basic specifications of this engine is given below-
By early 1938, this engine had been developed to produce 85 BHP by raising the compression ratio to 6.12 : 1 without changing the displacement, which begs this question-
By the mid-1930’s, Henry Ford had largely succeeded in doing what nobody else could, which was to make it possible for almost anyone in America to own a reliable car that was fitted with a V8 engine. There were of course other engine configurations available, but Henry Ford had done something else besides; he had found a way to reduce engine-manufacturing costs to the point where it was possible to sell millions of cars to ordinary people in the midst of a major economic depression, which was no small thing.
Nonetheless, Ford’s flat head V8 was not an overnight success. During the first two years of production, the flat head engine was plagued by manufacturing difficulties and major reliability issues that should have been resolved before the engine was released, but since Henry Ford was his own worst enemy in many ways, the first production models suffered from severe lubrication and balancing issues that would have overcome a lesser man.
Within three years of the engine’s release however, all of these issues had been resolved and the flat head V8 had started to earn a reputation as a reliable workhorse in passenger vehicles, light to medium commercial vehicles, and in countless military applications. Despite this though, the design of the engine was such that overheating issues were inevitable, and this remained a major problem up until 1953/54 when production of the engine ceased.
The overheating issue was a result of the exhaust gas passing through the cooling jacket through ports that were necessarily restricted where they passed between the two middle pistons in each bank of cylinders. The exhaust ports for the two outside pistons in each bank also passed through the cooling jacket, but on the outside of the cylinders. While Henry Ford saw this as a good thing, since this arrangement would (and did) reduce engine warm-up times, the cooling system on the first iterations of the engine could not cope with the high thermal loads imparted to the coolant by the hot exhaust gas, which resulted in the destruction of a great many flat head engines.
As a practical matter, the first engines’ cooling systems operated on the thermo-siphon principle, and therefore, these engines had no water pumps. The cooling system depended on hot coolant rising and cold coolant sinking to establish a circulation pattern, and while this arrangement worked reasonably well under light engine loads, it stopped working under high engine loads when the thermal load from hot exhaust gas exceeded the cooling system’s capacity to maintain a circulation pattern.
It was only after much opposition from Henry Ford that he very reluctantly agreed to the addition of engine driven water pumps to his engines in the mid-1930’s. However, while this did alleviate the engines’ tendency to overheat at high loads it did not resolve the issue, and as mentioned elsewhere, overheating remained a major problem until production of the engine in the USA ceased in 1953/54.
Despite the flat head V8’s propensity to overheat though, the basic engine design was licensed to many manufacturers in Europe and elsewhere, who continued production for many years after 1954. For instance, in France, the engine was used in Simca cars and trucks until 1961, while in Brazil, the flat head V8 engine saw service in cars and trucks until 1964 and in some military applications up to 1990.
Therefore, given the fact that Ford’s flat head V8 engine was in use until comparatively recently, it is obvious that it was not killed off by an inadequate cooling system. It might be worth noting at this point that while the development of overhead valve cylinder heads by an outside engineering concern eliminatedthe flat head V8 engines’ tendency to overheat completely, these cylinder heads were never manufactured in meaningful quantities due to their high manufacturing costs and serious design flaws that made them impractical for large-scale use.
By the standards of its time though, Ford’s flat head V8 engine was no better or worse than comparable engines made by competing manufacturers in terms of power output per unit of displacement, so it must have been killed off by something that affected all contemporary engines equally. In fact, Ford’s flat head V8 was killed off by something that affects and limits engine performance to this day, which you may surprised to learn is known as the-
While it would be tempting to say that Ford’s flat head engine was killed off by superior OHV technology, the fact is that OHV technology was already mature by the beginning of WW1 in 1914. In fact, aircraft of the time used OHV engines almost exclusively and while we need not delve into the reasons for this here, it is worth noting that OHV engines also outnumbered side-valve engines in the automotive sphere, which raises an interesting point.
This point is that by the time Henry Ford started development of his flat head V8 engine, OHV engines were no more efficient in terms of power delivery per unit of displacement than side valve engines of similar displacement were. While there were some exceptions to this rule, and most notably in the case of OHV engines made by Chevrolet, the differences were small and rarely exceeded about 6 percent or so in real terms. When viewed objectively, an improvement of 6 percent was largely meaningless, since it was completely offset by the significantly higher weight of the OHV engine, as well as by its higher manufacturing costs and increased technical complexity.
It is stated elsewhere in this article that Ford’s flat head V8’s design contributed to its demise, and while this is true it does not tell the whole story, so let us look at this design issue in terms of the engines’-
Volumetric efficiency
If an engine is perfect, it would suck in and expel a volume of air that is equal to its displacement, but due to frictional losses, this generally does not happen in naturally aspirated engines. However, in the case of Ford’s flat head V8, frictional losses were particularly severe since the inlet air had to make two 90-degree turns before it entered the cylinders. Moreover, when the exhaust gas exited the engine, it collided with the incoming intake charge during valve overlap, which further reduced the engines’ ability to breathe efficiently.
Another issue was that exhaust gas scavenging was extremely poor due to a), a built-in restriction in the exhaust port where it passed between the middle cylinders in each cylinder bank, and b), because the exhaust runners were of unequal length, and two exhaust runners on each bank merged into a single port in the cylinder block. The overall effect of this was that exhaust scavenging efficiency was greatly reduced by oscillating pressure waves resulting from the unequal volumes of the exhaust runners.
In combination, the factors described above produced a very poor volumetric efficiency value, but despite this, Fords’ flat head V8’s ran reasonably well and although the poor exhaust scavenging issue could be somewhat alleviated by polishing the exhaust ports, a more serious problem existed, which was the engines’-
Low compression ratio
The single biggest disadvantage of incorporating valves into the engine block is that the valves need to lift into a space in the cylinder head to work, which necessarily enlarges the volume of the combustion chamber, which in turn, reduces the maximum achievable compression pressure.
In practice, these issues presented Ford engineers with an insurmountable problem. For instance, the tops of the pistons could not be made to extend beyond the level of the cylinder block, because doing so would have diverted an unacceptably high percentage of the combustion pressure into the valve chamber. In fact, one of the major issues flat head engines suffered from was burnt valves due to much of the combustion occurring in the valve chambers, instead of all of it occurring directly above the pistons. While removing material from the cylinder head would decrease the volume of the combustion chamber and thus increase compression pressures, doing this would however, limit the space available for valve lift.
The only way around this issue was to fit larger valves to increase the volume of the intake air, and, although some versions of the flat head V8 achieved compression ratios of 6.12 : 1 in this way, higher compression pressures meant higher combustion temperatures, which greatly increased the chances of the engine overheating. This, in turn, largely defeated the purpose of raising the compression ratio in the first place.
While OHV engines had none of these problems, they were nevertheless no more efficient than the average side valve engine in general, and Henry Fords’ side valve V8 engines, in particular. From our modern perspective then, it would appear that side valve engines were killed off by their low compression ratio and poor volumetric efficiency that combined to produce low power outputs, but this would not be entirely correct.
The fact is that all engines suffered from much the same issues during the 1930’s, irrespective of their valve trains, and although we now consider compression ratios and high volumetric efficiencies as the end all and be all of engine design and therefore, engine performance, things were vastly different in the decades immediately preceding and following WW2. As a matter of fact, the real problem that engine designers had to overcome in the 1930’s still exist today, so let us look at this problem that is known as the-
Today we recognise the fact that poor quality fuel can cause all manner of driveability issues in modern engines, and the quality of fuels that are available today is the main factor why compression ratios on modern petrol engines cannot be raised beyond 16 : 1 at the upper limit.
However, even the poorest quality fuel that is available today is still light years ahead of what was available in the 1930’s, but unlike us, the engineers of the 1930’s did not have the luxury of hindsight; all they had to work with was the fuel that was available then, and that fuel did not allow high compression ratios. At issue is the fact that by 1925, empirical research data had not only shown that a direct correlation existed between fuel quality, a fuels’ chemical properties, compression ratios, air/fuel mixing, ignition source, and internal engine geometry, but also that each of these actors directly influenced engine efficiencies, both individually, and collectively.
One particular researcher, H.L. Horning, published a research paper in 1923 titled Effect of Compression on Detonation and its Control(SAE Technical paper No. 230033), in which he stated that (paraphrased) ...“knock (premature detonation of fuel) is not only dependent on engine operating conditions, ...and ... that the incidence of [knock] is in fact directly proportional to both some power of the [energy] density of the fuel in the air/fuel mixture, and some power of the absolute temperature [of combustion].
In translation, the above excerpt merely means that premature ignition of an air/fuel mixture in an engine is inextricably linked to both the composition/chemical properties of fuel, and the compression ratio of a given engine. However, Horning was not the first researcher to discover this relationship; he was only among the first researchers who quantified the problem.
In fact, the first attempts to reduce premature ignition date back to the 1910’s, and it was only in the early 1920’s that researchers discovered that the addition of small amounts of tetraethyllead (discovered by the Du Pont chemical company) to fuel eliminated the issue. Interestingly, the discovery is described in the flowing manner in the notebook of one researcher, named Thomas Midgley - “The ear-splitting knock of their test engine turned to a smooth purr when only a small amount of the compound [tetraethyl lead] was added to the fuel supply [and]all the men danced a non-scientific jig around the laboratory.”
While this discovery proved to be an economically viable way to improve the fuel of the time, well documented concerns about the serious health risks associated with using tetraethyllead to increase the resistance of fuel to knocking meant that the octane rating of fuel was pegged at only 60 RON (Research Octane Number) in 1930. Moreover, this high-tech fuel was not available everywhere in the USA, and would not be for at least another 10 years or so.
Thus, when Henry Ford started developing his V8 engine, the fuel that was available to him had only a limited resistance to knocking, and it is against this historical background that both the success and eventual demise of the flat head V8 must be judged. Put in another way, Henry Ford and his engineers (as were other manufacturers) were forced to design the airflow dynamics of their engines around the limitations of the fuel that was available to them.
The 1930’s is now known as the” Power Wars” age in the history of the development of commercial fuels, but this war had little to do with the battle between engine designers to improve the power output of their engines. Instead, it had everything to do with the power struggle between car manufacturers, the Society of Automotive Engineers, fuel companies, and the Surgeon General. Essentially, the war revolved around the maximum allowable amount of lead that could be added to fuel, and although the upper limit was never legally defined, a sort of gentleman’s agreement was entered into between all parties involved that limited the RON octane number of commercially available automotive fuel to 60 almost right up to the start of WW2.
The practical effects of the Power Wars on the American automotive industry were profound, in the sense that fuel with an octane rating of 60 resisted all efforts by engineers to raise engine compression ratios beyond the 6 : 1 range- simply because the available fuel was not sufficiently resistant to premature ignition to allow higher compression ratios.
So, did poor fuel quality kill off Henry Ford’s flat head V8? Well, yes, and no. Yes, in the sense that poor fuel quality prevented further development of the engine, and no, in the sense that not only this particular engine was eventually killed off. In markets outside of the USA where the flat head V8 saw service well beyond the 1950’s, improved carburetion and other modifications allowed compression ratios to be raised to the point where fuel with higher (than 60) octane ratings could be used until emissions regulations prevented further use of the engine.
It is said that nothing drives technological developments in quite the same way that major wars do, and in the USA, the advent of fuel with an average octane rating of 79.81 in the early 1950’s allowed higher compression ratios, which then averaged about 6.86 : 1. This in turn, allowed engine designers to take advantage of the inherently better volumetric efficiencies of OHV engines, and it is the combination of these two factors that killed off Fords’ flat head V8 (along with all other low compression engines) more effectively than any design flaw or characteristic the flat head V8 engine might have had.
The advantages that improved fuel quality brought was not lost on the Ford Motor Company. In the very early 1950’s, the company started development work on an OHV V8 to replace the flat head engine, and by 1954, the first production version of the Y-block engine had a displacement of 239 cubic inches (3.9L), developed 130 BHP (97 kW) at 4 200 RPM, 214 lb/ft (290 Nm) of torque, and had a compression ratio of 7.2 : 1, all of which represented major advances over flat head Ford V8’s in standard trim.
However, although the Y-block family of engines was superior to competing engines in some respects it suffered from serious lubrication issues and a severe displacement limit, and therefore had a short production run. Nonetheless, the major advances of this engine over the flat head engine were due solely to improved fuel that had made it possible to raise compression ratios to above anything that was possible with flat head engines- regardless of the manufacturer.
