(first posted 3/20/2011) Nailhead: what did Buick do to deserve that less than flattering name for its legendary V8 engine from the mid-fifties to the mid sixties? Hemi-head; even flat head are much more lyrical. For those not familiar with Buick’s unusual valve arrangement, we’ll do a primer on that, as well as touch on its brief glory days on the drag strip. But for those already enlightened on the subject, I offer something more: the source and possible explanation of its unusual valve arrangement.
Buick came late to the OHV V8 game, Cadillac and Olds both having introduced their superb engines in 1949. Buick’s venerable straight eight from the thirties at least had overhead valves, unlike the previous Cadillac and Olds flathead engines. That allowed it to stay in the post war game a bit longer with higher compression and multiple carburation. But it was heavy, and not at all suitable for a the horsepower war of the fifties that was quickly developing.
In 1953, Buick brought out their new V8, with a very large 4″ bore and quite short 3.2″ stroke, the most oversquare engine on the market at that time. It displaced 322 cubic inches (5.3 L) , and came in 164 to 188 hp variants. In 1954, a small-bore version with 264 CID (4.3 L) reserved for the low end Special arrived.
The new Buick V8 was rather light and compact for its time, weighing some 625 lbs. It was built with very high quality forgings, and quickly caught the eye of hot rodders, this being a few years before the Chevy small block came on the market. Its unusual head and valve arrangement made it a narrow engine, increasing its appeal to engine swappers, like this one replacing the six in an old Chevy. But it was precisely that narrow head that also presented serious challenges.
Here’s a nice cutaway of the Buick nailhead engine. What instantly stands out is the unusual arrangement of the valves and valve train, in that they hang vertically in a pent-head or almost hemi-head combustion chamber. We’ll discuss the origins of this later, but note how tortured the exhaust port is, having to make an almost 180 degree bend right behind its valve.
Just for comparison sake, here’s a cross section of a more typical V8 (AMC). The valves have a mild angle in relation to the head, creating a more typical “wedge head” combustion chamber. Perhaps the most obvious thing about the Buick nailhead is that its arrangement demands very small valves, which seems antithetical to the whole concept of the modern V8 in the first place.
And small they were, hence the “nail head” moniker. The early engines had a 1.75″ intake and a 1.25″ exhaust valve, puny even for the mid fifties. Even the legendary Wildcat 401 from the mid sixties had only a 1.875″ intake and a 1.5″ exhaust; both substantially smaller than the much smaller Chevy engine.
The explanation generally given is that Buick was focusing on torque rather than maximum breathing at high rpm. And the Buick engines delivered that in spades, typically with more than one ft. lb. per cubic inch, a very respectable output indeed. In the sixties, Buick labeled and advertised their engines on their torque output, not the horsepower, which can be confusing. This Wildcat 445 is a 401 from a 1966 Skylark GS with 325 hp.
Buick had to use very aggressive camshafts in order to make the nailhead work. By opening the little valves early, and very quickly, much of their limitations were overcome, up to a point. Already the first 322 nailhead had a camshaft that was the equivalent of a “super race cam” at the time; one that would be typically installed from an aftermarket supplier. The intake duration was 282 degrees, and the exhaust 292 degrees, with a 67 degree overlap, along with very steep ramps for extra rapid valve opening.
The camshaft in the 401s were even more aggressive, and those engines were known for their lumpy idle. Not exactly the image Buick typically was trying to convey at the times, with a banker’s Electra 225.
Hot rodders found out early that the Buick’s breathing limitations could be overcome by creative solutions. Intake manifolds with every possible combination of carburetors known to homo hotrodius were fabricated.
Supercharging was an obvious route, by forcing more air through the small ports. Here’s an excellent reprint of a 1954 Hot Rod Magazine article detailing perhaps the first blown nailhead (above), with gobs of technical info on the then new Buick engine.
Hot rodders were drawn to the Buick nonetheless, at least for a few years before the Chevy and Chrysler hemi established their supremacy. Undoubtedly the most creative and bizarre one of all (above) reversed the valve arrangement totally, using a front crank-driven blower to force air through the tiny tortured exhausts, allowing the larger and smooth intakes to now function as exhausts. Take a close look: unbelievable!
The biggest racing fan of the nailhead was TV Tommy Ivo, who started with one in his very successful rail, added a second, and eventually built this legendary quad-nailhead four wheel drive monster. Here’s more nailhead racing history.
The nailhead eventually grew to 425 cubic inches in 1963 for its final three years. In 1967, a whole new Buick generation of V8s appeared, with a very conventional head indeed. I suspect that that the Buick’s pent head was notoriously dirty, and Buick saw the writing on the wall in terms of the coming emission regulations. It’s a curious contrast to the Oldsmobile V8, whose combustion chamber was the exact opposite: it had a very shallow valve angle, and the basic Olds combustion head design survived as one of the last of its breed; in fact the Olds 307 was the last V8 to meet emission regs with a carburetor in 1990.
So now to my theory about the origins of the nailhead’s unusual design. In 1951, Harley Earl’s famous LeSabre concept appeared, with a radically advanced 3.5 liter (216 CID) aluminum V8 that ran on both gas and methanol. It was supercharged and was rated at 339 hp. Years ago, as a kid, I stumbled on a cross section of the LeSabre engine, and was struck by a certain specific similarity to the nailhead.
The little Buick engine had hemispherical/pent roofed heads, but with its valves in the classic formation allowing for large valve diameters. If you look at the intakes on this, one can see that the nailhead used the same unusual arrangement, but for both its valves. The LeSabre/XP 300 engine’s exhaust push rods had a wild arrangement, and were designed to fit into the block between each cylinder.
I can’t help but assume that this first OHV engine by Buick showed a strong interest in the hemi/pent roof head, and that perhaps Buick even considered building a true hemi version of the nailhead (Chrysler hemi above, with more typical pushrod/valve train configuration). Or it least, that was the starting point. if so, it rather backed them into a corner, with little valves and a combustion chamber that in the longer run was not so ideal.
The way to really look at the nailhead is this: it’s similar to a typical four-valve per cylinder head of today, but with two of the valves missing. That’s negating the whole advantage of the hemi head: room for more and/or bigger valves. Buick took a half step, but one that left an enduring legacy nevertheless.