Buick’s XP-300 Motorama dream car included a number of features that would eventually find their way into GM production vehicles.

The 1951 LeSabre from General Motors has often been called the most famous concept car in history. But meanwhile, the LeSabre had a sibling that isn’t nearly as famous, but probably had a greater influence on future GM products: the Buick XP-300. Since the term “concept car” didn’t exist in 1951, the company crafted another name for the project: “experimental laboratory on wheels.” That’s quite a mouthful, but it’s a fair description of the XP-300. Elements of both its styling and engineering would be featured in Buick production cars a few years later.

The LeSabre/XP-300 project expanded from one vehicle into two, reportedly, when the two GM executives in charge of the program, styling chief Harley Earl and VP of engineering Charles A. Chayne, gathered up so many ideas that they needed two cars to showcase them all. The LeSabre, it was decided, would be Earl’s pet project while the XP-300 (its original designation was XP-9) would be Chayne’s. Like Earl, Chayne was a passionate car enthusiast. The priceless Bugatti Royale now in the collection of the Henry Ford Museum was donated from his personal collection.

The XP-300’s body shell was fabricated in heat-treated aluminum sheet attached to a steel tubing superstructure, which was then welded to the frame to form a unitized structure. Of chrome-moly box-tube construction, the chassis featured torsion-bar IFS and a De Dion rear axle, all rolling on a 116-inch wheelbase. Overall length was 192.5 inches, while the total height was just 53.4 inches at the top of the windscreen.

One of Earl’s favorite developments, the wraparound windshield would first appear on GM production cars in 1953 and was eventually adopted across the board by the automaker. The XP-300’s distinctive teardrop-shaped headlamp bezels became a Buick production feature in 1953 as well, and the fine-toothed, electric-razor grille texture can be found on the 1957 Buicks. No doubt we can find more production-ready ideas if we take a closer look.

The aluminum V8 in the XP-300 was a twin to the one in the LeSabre with an aluminum block and aluminum cylinder heads with hemispherical combustion chambers. With  perfectly square 3.25-inch bore and stroke dimensions, displacement was exactly 215.69 cubic inches, while high-domed pistons provided a compression ratio of 10:1.  Output was a claimed 335 hp with the aid of a Roots blower (a GM specialty thanks to its two-stroke diesel expertise) and a tandem fuel system that could supply gasoline or methanol on demand. The transmission was a modified Buick Dynaflow.

While the advanced GM V8 never made it to an assembly line, parts of the design made their way into the production Buick V8 introduced in 1953, the engine commonly  known as the Nailhead. (See our feature on the Nailhead here.) The unusual intake-valve setup with underhand rocker arms was used on both the intake and exhaust valvetrain on the Buick production V8, which remained in the division’s lineup through 1966.

In contrast to he other vehicles in the glamorous Motorama show car fleet, the cockpit of the XP-300 was remarkably spartan and businesslike, which can be taken as a reflection of Chayne’s personal taste—his interests included European vintage cars and all things Bugatti. Like the LeSabre, the XP-300 was a fully functional road car and it racked up more than 10,000 miles, many by Chayne himself, and as the story goes, he personally topped 140 mph in it at the Milford Proving Ground. (See a video of the car in action at Milford here.) In 1966, GM restored and donated the car to the Sloan Museum in Flint, Michigan, now part of the Flint Cultural Center, where it can still be seen today.