In 1961, Pontiac created the Tempest Trophy 4 by cutting a 389 V8 in half. Hot rodder Mickey Thompson did the factory one better and cut the four in half to create a twin.

The most obvious question is, “Why?” For what purpose would Mickey Thompson, the hot rodder’s hot rodder, create a tiny, two-cylinder Pontiac racing engine? For the greater glory of his sponsor Pontiac, of  course. In July of 1961, Thompson gathered a fleet of four Pontiac race cars on the 8,000-ft runway at March Air Force Base near Riverside, California. The plan: to attack an entire catalog of FIA and USAC records for the standing-start mile and kilometer.

One of the existing records that looked ripe for the picking was the Class F mark for vehicles displacing from 1000 cc to 1500 cc (91.53 CID). The record had been set back in 1937 on the Autostrada by Giuseppe Furmanik in his Maserati 4CM streamliner. Of course, Pontiac didn’t produce any engines nearly that small at the time, and only a Pontiac would do. So M/T created one by sawing a four-cylinder Tempest engine in half.

The Trophy slant 4, created by Pontiac by borrowing the left bank of its standard 389 cubic-inch V8, was a fairly interesting engine in itself (see our feature here). Thompson and crew, led by his legendary shop wizard Fritz Voigt, took a production Tempest 4 block and carefully amputated the front two cylinders, then sealed off the opening with a .375-in. aluminum plate. This thick plate was fastened into the block webbing all over with dozens of tiny, countersunk machine screws, while also providing a suitable mounting point for the timing cover and accessory drive. The cylinder head was fashioned in much the same way by cutting down and plating a V8 head casting.

Moldex of Detroit supplied the heavily counterweighted crankshaft with the rod throws phased at 0 and 360 degrees, the classic British motorcycle arrangement. With its stock 4.060-in bore and shortened 3.50-in stroke, the twin displaced 90.73 cubic inches. Pistons, rods, and other hardware came from the M/T speed equipment catalog. The petite belt-driven Roots blower, which reportely produced a healthy 25 psi of boost, was from a GMC 2-71 diesel, an engine typically used to power generators. A Hilborn fuel injection pump and water pump were driven from the rear of the blower.

The sawed-off Tempest twin was installed in the smallest of the  M/T record cars, naturally, a lightweight Dragmaster dragster chassis (above) where it was coupled to an ancient LaSalle three-speed transmission. Unlike the others, the dragster lacked any aerodynamic assistance. Still, the tiny flyer managed an average speed of 91.369 mph in the standing-start kilometer and 106.78 mph in the mile, easily eclipsing the Maserati records.

Of course, even in a small dragster, a 106+ mph average in a standing mile requires a significant amount of power. On the M/T dyno in Long Beach (below) the Pontiac twin reportedly produced 257 hp at 5,500 rpm with the aid of a medium dose of nitromethane fuel. That’s nearly 3 hp per cubic inch—quite respectable for 1961, especially for an ad hoc hot rod.

For more about the M/T twin, there are two articles in the September 1961 issue of Hot Rod magazine that cover it in detail, and from which we borrowed much of this material. The engine and its chassis, still in fine original condition, can be seen at the NHRA Wally Parks Museum in Pomona, California.