GM/s most famous dream car, the 1951 LeSabre, has an equally remarkable engine under the hood: an experirmental V8 with a bunch of exotic features.
Approved in the spring of 1947, the LeSabre dream car was a moon-shot effprt at General Motors, with a reported budget of more than $1 million ($13 million today). A pet project of GM vice president of design Harley Earl, it soon spiraled up into a two-vehicle program, with a second car, the Buick XP-300, for Buick chief engineer Charles E. Chayne. Both the LeSabre (XP-8) and Buick XP-300 (XP-9) were powered by the same remarkable engine: an experimental 215 cubic-inch V8.
With a dead-square bore and stroke of 3.25 inches, the total displacement works out to 215.69 cubic inches—surprisingly small compared to the GM V8s then going into production, the 303 CID Oldsmobile and 331 CID Cadillac. Block and cylinder heads are aluminum castings with two valves per cylinder, hemispherical combustion chambers, and high-domed pistons that yield a compression ratio of 10.0:1. Atop the intake manifold is a GMC-Detroit Diesel Roots blower with twisted three-lobe impellers, driven from the crankshaft by three V-belts and capable of 18.2 lbs of boost.
Of course, the first thing to catch your eye is the outlandish valvetrain. The intake-valve layout is fairly conventional, and it’s similar to that of the production 1953 Buick V8. (See our Nailhead V8 feature here.) But on the exhaust side, the pushrods are horizontal and actually pass between the cylinder liners in the block to drive the sodium-cooled valves. Thus the exhaust rocker arms are aligned 90 degrees from the intake rockers and parallel to the crankshaft—sideways, in other words. The camshaft and solid lifters were housed not in the block casting but in a separate carrier integral to the intake manifold. Needless to say, these particular features never found their way into a GM production V8. The 1961 Buick aluminum 215 CID V8 is but a distant cousin.
Here’s a somewhat different cutaway drawing that includes the induction system. There are actually two complete, parallel fuel systems, one for pump gasoline and the second for pure methanol, enabled by two Bendix-Eclipse two-barrel aircraft carburetors and a pair of separate fuel tanks in the trunk. In normal operation the engine runs on gasoline alone, but when the throttle pedal is pushed to the floor, an electrically-operated fuel valve opens and the methanol system is kicked into action.
According to GM’s dynamometers, in methanol mode the LeSabre/XP-300 V8 could produce up to 335 hp at 5,200 rpm and 381 lb-ft of torque at 3,650 rpm. We pause to reflect how stunning that was for a road car engine in 1951: That’s 266 lbs BMEP and 1.55 horsepower per cubic inch. At the time, the Motor City’s most powerful production engine was the 331 CID Chrysler hemi V8 with 180 hp, or .54 hp per cubic inch.
Installed in the LeSabre (below), the prototype V8 itself is barely visible, hidden under the complex twin fuel systems and a pair of large air cleaner canisters. When you look under the hood, there’s little hint of all the crazy magic going on underneath. Both the LeSabre and the XP-300 are still around in operating condition, the LeSabre in the GM Heritage Collection and the XP-300 at the Sloan Museum in Flint, Michigan.
I had a ride in the LeSabre at the 2003 Eyes on Design show, held at the GM Tech Center. It felt like a conventional 50+ year old car, and I had no idea how interesting it was from an engineering standpoint.
What an extraordinary engine. Thanks for bringing out the details.
This car is unique to ALL the other cars made by General Motors, as it doesn’t bear the name of a make [Like Chevrolet, Buick, Cadillac, etc]. It’s name was simply LeSabre, by GM. ,
Harley Earl himself drove the LeSabre to the 1951 [or ’52, can’t remember for sure] Watkins Glenn Grand Prix race, and it was the official pace car for the race.
Many years ago at a local auction I bought a selection of developed, but unpublished, black & white rolls of 35mm film, and the photographer’s name on the packages was Steinberg. As I went thru the negative rolls, I discovered this guy had been a racing enthusiast, and had taken photos of the Watkins Glenn races. Included in the negatives is a shot of the LeSabre leading the pack with Harley Earl driving. I’ve still got the negative and I enlarged the photo, framed it, and it’s now hanging in my house.
In the picture of the rear of the motor it looks like there is no transmission, but I can see something that looks like a universal joint. Was the transmission incorporated into the rear differential ? If it was that would make sense because the car was so low, it would be an attempt to create more foot room on the front floor board.
Yes, it was a transaxle, Initially a Dynaflow and later a Hydra-Matic. The Cadillac Cyclone is also equipped with a Hydra-Matic transaxle.
I happen to be talking by phone to a retired GM stylist last night, who while he was at GM much later, knew the answer to Chris Lukens question, but MCG beat me to it.
My contact said that the Dynaflow couldn’t handle the power of that supercharged engine, especially with Earl’s lead foot, as he drove it almost daily! The final drive on the LeSabre was the basic concept that became the Pontiac Tempest rear axle/gearbox 10 years later.