During the era when real grassroots hot rodders could still race at the Indy 500, renowned land speed racer Barney Navarro shocked the motorsports world when he clocked 150-mph qualifying laps with a six-cylinder engine in 1967. Due to chassis tuning issues, Navarro's car didn't make the final cut for the race, but his lap times still stand as the fastest ever posted by a six-banger. The engine in question was a 199ci AMC inline-six, the same putt-putt mill anyone could get in a Rambler or Gremlin. Navarro liked the idea of a six-cylinder crank supported by seven main bearing caps, and the engine's over-square 3.750x3.000-inch bore and stroke dimensions were appealing as well. With a built short-block and a custom turbo system dishing out 105 psi of boost, the little six produced 700 hp. That was with the stock cylinder head, block, and rocker arms. Even if they don't realize it, the few remaining Honda drag racers weren't the first ones to combine small-displacement inline engines with a ton of boost.
If there's an oddball in this group of great, forgotten engines, it's the Buick nailhead. If the flat 12-degree valve angle of the late-model LS7 impresses you, take the nailhead's zero-degree cylinder heads on for size. That's right, the nailhead's valves were positioned vertically over the combustion chambers. Furthermore, the nailhead used shaft-mount rockers that were positioned outboard of the valves, pivoting inward toward the intake manifold. The jury's out on whether this unique arrangement had any positive or adverse impact on performance, but it certainly looked strange. Bench racing aside, in reality flattening the valve angle without optimizing the intake port inlet location severely compromises airflow, and the Buick's induction path was convoluted for sure. The benefit was that it resulted in an extremely compact package that wasn't nearly as wide as its fellow V-8 contemporaries. Furthermore, nailheads boasted rugged forged cranks and rods-which when combined with its compact dimensions-explains their overwhelming popularity in roadsters during the late '50s.
The first-generation nailhead was built from '53 to '56, and was offered in 264 and 322ci configurations. The nailhead's small valves looked like nails, hence the name, and yielded high-velocity ports with conservative cross-sectional area. The result was a torquey engine that generated more than 1 lb-ft per cubic inch, which was outstanding for the era. The second-generation nailhead was produced from '57 to '66 in 364-, 401-, and 425ci configurations. From '64 to '66, the 425 was the top dog in the nailhead camp, kicking out 360 hp and 465 lb-ft of torque. It featured a 4.312-inch bore, a 3.640-inch stroke, 10.25:1 compression, and dual four-barrel carbs. There is no consensus as to why Buick cancelled production of the nailhead, but it was replaced by the familiar 400/430/455 family of big-blocks in 1967.
While foreign elitists love ripping on our primitive, big-inch, pushrod engines, they often replace their high-tech, high-winding, turbocharged, weenie-displacement slugs with red-blooded American lumps.