Talk About "Forgotten GM Muscle"... [PIC]

In 1963, Pontiac was looking for a way to stay in drag competition. With the full sized Catalina 421 Super Duty was competitive in NASCAR, it was way too heavy for the strip even after turning the chassis into swiss cheese, so they decided to muscle up the '63 Y-body Tempest in 1962, under Mickey Thompson and Royal Pontiac, replacing the 326 V8 (actually 336) with the new 421 which was basically a bored out 389. The engine drop in was easy as the blocks for all 3 engines were identical in dimension. Pontiac authorized 2 prototype "mules" and after testing, 12 were built ... 6 poster coupes and 6 station wagons. Abruptly, in early '63 GM put out a racing ban and the project was terminated. The 421 SD Tempest did quite well on the track with the one weak point being the transaxle. After 10 to 12 runs, the teeth on the small 7.5" ring and pinion would be chewed up. The transaxle ratio was limited to 3.90 when optimum performance required a 4.11.  Later mods involved installing a more conventional transmission and rear axle set up. 4 of the original 421SD Tempests still exist today. The following year, the larger next generation Tempest would offer the 389 V8 but not the 421 SD.

This test mule model is by H-61 and was released 20 years ago.