Network
It’s safe to say that pretty much anyone reading this is an enthusiast. As such, regardless of your brand affiliation, you owe something to the Flathead Ford V8 engine. While it wasn’t the first V8 engine to grace an engine bay, it was the first one to see mass-production and mass-market acceptance, making the V8 engine an everyman’s engine.
As such, it’s no surprise that when hot-rodding really took off in the 1950s, the Flathead was the object of gearheads’ attention. A low-cost, affordable powerplant meant they were the perfect engines to tinker with at the time, even though it took significant resources to get them on par with the performance of a modern powerplant.
While advances in automotive technology might have rendered the Flathead lacking in the power department compared to its modern contemporaries at the time, it enjoyed significant aftermarket support. An inexpensive V8 engine with a solid aftermarket, whether you’re in the mid-20th century, or in the early 21st century is a combination that leads to great things.
No modern molded-rubber crank seals here. Dorton uses a modern version of a traditional rope gasket from Best Gasket. Replacing the asbestos original, the new seal uses graphite impregnated braided Teflon.
Our friend Jeff Huneycutt over at The Horsepower Monster teamed up with Keith Dorton of Automotive Specialists to cover the work being done to an almost completely stock rebuild of a vintage flathead, which gives us a solid look into the oddities and eccentricities of the iconic engine. We say almost stock, because while the owner wants a period-correct piece, he wants more power than the original models, which struggled to break into the triple-digit horsepower range.
Dorton decided that the answer to the problem is to add stroke to the engine. That leaves the block in stock configuration without any extreme machining, while adding both displacement and compression in a relatively easily reversed configuration, should he ever want to take the engine back to completely stock.
Since the traditional flathead didn’t even have a provision for an oil filter until the 1940s (and when one was added, it only filtered about 10 percent of the engine’s oil) Dorton did perform a modification to the block’s oiling system to allow the use of a modern canister filter.
Starting with a 1944-vintage 239 block, the original bore and stroke were undersquare with a 3.1875-inch bore and a stroke measuring 3.75 inches long. Additionally, the factory compression ratio started with a “6” due to the poor chamber design and the poor fuel quality back then.
Using a Scat crankshaft, the stroke is increased to 4.250 inches. While the crankshaft looks vintage to the naked eye, besides the additional stroke length, the crank also uses a traditional small-block Chevy rod journal. The crank rests in the Flathead’s signature three-main-bearing block. The bearings used are modern babbitt style, as opposed to the poured babbitt bearings that came standard, originally. They have their work cut out for them, as the crank weighs in excess of 60 pounds.
The Flathead’s three main bearing configuration was simply a cost-cutting measure in the original design. The missing mains definitely hurt overall performance.
The owner did consent to a significant (by Flathead standards) overbore, with a final bore size of 3.3125 inches. The brings the total displacement up to 293 cubic inches. Filling the bore is a set of Mahle forged pistons with a shortened 1.313-inch compression height, allowing the use of 7.000-inch long Scat H-beam rods. The pistons also feature a modern slipper skirt design with Mahle’s Grafal piston skirt coating. The new combination comes in at a whopping 8.4:1 compression ratio.
The camshaft is an Isky Cams “3/4-Race” grind, with .364 inch of lift on both the intake and exhaust lobes, along with 226 degrees of duration at .050 inch of valve lift (again, intake and exhaust) with a 111-degree lobe separation angle. A gear-drive timing setup is standard from the factory, but OEM, the gear was made from a fiber material. In this modern rebuild, the timing gears are made of aluminum.
Check out those Scat H-beam rods. They are so narrow, they might pass for I-beams. Also, you might wonder why, if there are no valve reliefs on the pistons (since the valves are nowhere near the piston in a Flathead) why the pistons are directional. The answer is, the pistons are manufactured with an offset pin bore, making them directional.
Unlike any modern engine, the Flathead’s entire valvetrain is contained within the engine block. The heads are just valve and cylinder covers with combustion chambers cast into them and no moving parts. The lifters are a solid flat tappet design with an interference-thread bolt screwed into them to be able to adjust valve lash.
The flathead uses the same size intake and exhaust valves — both 1.500 inches in this case — and Isky valvesprings with 80 pounds of seat pressure and 200 pounds of open pressure. Another oddity of the flathead is the valve guides. They are O-ringed devices that fit into the bore in the block and are retained via a spring clip. The valve, spring, guide, locks, and retainer are all assembled outside of the engine and installed as a single unit.
There's a whole lot to unpack here. Starting from the upper left, the camshaft is an Isky "3/4 Race" model of internet lore. Top, right is the valve and valvespring combination, which was identically sized (1.500 inches) for the intake and exhaust. On the bottom left is the unique solid lifter, which was little more than a slug with a bolt screwed into it to adjust lash. On the bottom right is the valve guide, which fit in the valve bore in the block, and was retained by the O-ring and the silver spring clip.
Surprisingly, the cylinder heads are held on with 24 (yes, twenty-four) studs per bank of cylinders. That’s a big testament to how far modern materials have come, with much higher cylinder pressures being contained by fewer (and smaller) fasteners.
The one externally visible non-traditional touch Dorton put on the engine was a modern distributor. Driven directly off the end of the cam, like the original, the present-day distributor is a cap and rotor design. Topping off the combination is an Offenhauser manifold with provisions for dual two-barrel carburetors.
It seems almost comical that the Flathead used 24 head studs per bank to hold the simple almost valve cover-like cylinder heads down, especially considering that in stock form the engine has so little cylinder pressure.
The carburetors used are Primary 9 Super 7 carburetors made by Speedway Motors, which are based on the Stromberg Super 97 carburetors, but made of cast aluminum, instead of the original cast iron. With the engine buttoned up, it was time to bolt it up to the pump and see what kind of numbers the almost 80-year-old engine was capable of.
A peak horsepower output of 170.1 horsepower at 4,300 rpm and peak torque of 242.5 lb-ft at 3,300 rpm may not seem like anything stellar, but that’s a 70-percent increase of this model’s factory output.
We’ve only scratched the surface of the engine in this article. For the full breakdown, make sure to watch the video above. There are so many things about the Flathead that make you scratch your head, it’s hard to believe it played such an integral role in the history of hot rodding and the performance industry.
While this graph isn’t spectacular by any modern standard, if you consider it in context, 170 horsepower and 242 lb-ft of torque means the engine made 70-percent more power with relatively minor modifications, which are all reversible down the road.
