Diagram Single Barrel Carburetor 69 Chevy 6 Cylinder Engine

– Posted on January 6, 2021

(first posted 3/20/2011. Updated 1/5/2021)    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 flathead 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 likely 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 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 relatively light and compact for its time, weighing some 625 lbs. It was built with high quality components, 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 the Cadillac V8 that preceded the Buick by two years. The bigger valves have a mild angle in relation to the head, creating a more typical wedge head combustion chamber. The ports are bigger and smoother, especially the exhaust. 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.

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 V8 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.

But 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.

Pages: 1 2

Posted by: emeliaallise016795.blogspot.com

Source: https://www.curbsideclassic.com/automotive-histories/automotive-history-the-legendary-buick-nailhead-v8-and-the-source-of-its-unusual-valve-arrangement/

Berbagi :