Buick had built experimental cars beginning with the Y-Job in 1938. They built and drove the car while working out and testing new innovations. It was, as they called it, an "experimental laboratory on wheels" bringing about such production features as electrically activated convertible tops and windows, recessed tail lights, and flow-through fenders, as well as many mechanical improvements.

In 1946, GM decided the Y-Job had served its purpose, and decided to build a successor. There were so many innovations wanted by both stylists and engineers, that they decided to build two experimental cars: the LeSabre and the XP-300. Both were built with the same overall goal: To build an extremely high-performance car without sacrificing passenger comfort or ease of handling.

This article will focus on the XP-300. The name is what is implied: Experimental Project with 35 horse power.

The XP-300's power plant was an experiment to see what could be done if there were no limitations on fuel and material costs (those were the days!). The V-8 supercharged engine was classified specifically for the car by Buick engineers, and weighed 550 lbs, developing 375 horse power. The cylinder head and crank case of the XP-300's 90-degree V-type engine were made of aluminum. The exhaust valves were sodium-cooled. The engine was supercharged by a blower developed by GM engineers for diesel engines. During ordinary driving, the engine runs on premium fuel. When the accelerator is depressed past halfway, this opens a second carburetor which feeds methanol into the combustion chambers to supply a power boost. The engine was coupled to a specially-built Dynaflow transmission driven at slightly less than engine speed in order to fit the characteristics of a production torque converter to those of the XP-300's special engine.
The steering wheel was adjustable in or out, and the seats could be individually raised or lowered as well as forward or back by a push button hydraulic mechanism. The seats also had adjustable contour seat backs which could be changed to suit different drivers, even while the car was in motion if the driver or passenger so desired. A unique hydraulic jack system operated from the dash, lifted the car for tire changes before the driver left his seat! The convertible top featured a rear window that could be lowered while the top was up. It had a wraparound windshield that was supposed to eliminate wind noise so that passengers could talk at a normal level when the car was going 95 mph.


The XP was a low, sleek, two-seat convertible, sitting on a 116" wheel base with an overall length of 192.5'  and an overall height of 53.4'.  The ground clearance was 6.6" and it was 80" wide. Another unique feature was the hood which opened from the rear and tilted toward the front, as many performance cars would in years to come. It was raised and lowered hydraulically from the instrument panel.

The front end styling was more angular and less rounded as were the other car being made at the time. The front end would inspire the all new-for-'54 Buick line. The long louvered chrome panels along the side were functional. The louvers ahead of the door openings as well as those in the front third of the door allowed air to escape from the engine compartment, helping to prevent overheating. The louvers at the rear of the door opened into the driver1 s compartment and were adjustable to permit air to flow into the interior of the car. In the rear in the center of the long fin on the rear deck was a circle looking very much like the rear of a jet engine, which in reality was the backup light. The XP had two fuel tanks located behind the front seat, one for the methanol and one for the premium gasoline.


The body's structure was made from steel with an aluminum skin to keep the weight down. It was of unit body construction, with the frame and body welded into one solid unit. The frame was chrome molybdenum steel box type designed for maximum rigidity. The rear end was on coil springs while the front end rode on torsion spring construction.

Extra-wide brake drums were used, housing a double set of brake shoes which were cooled by forced air. The front brakes were on the wheels and the rear brakes were on the differential.

There was a combination speedometer/tachometer mounted over the steering column. The other instruments were mounted across a shallow board and on a floor pedestal between the seats. The clock was a combined clock, stop watch and elapsed time stop watch. The vacuum gauge was used in conjunction with the tach, allowing the driver to determine approximate horse power the engine is delivering on the road. The fuel gauge could be switched to show both tanks, and the oil level gauge could be switched to show transmission level. The other instruments were for water and battery. All the instruments were round-faced aircraft type, typical of Harley Earl's influence. Earl's team and GM's willingness to fund the project helped to make those great cars of the '50s and '60s that we all love today. Keep 'em driving!