Toro-Flow

The Other GM Diesel

- Jim Allen

The ’70s TV talk show host Tom Snyder was known for asking, “What goes through their minds?” when confronted with inexplicable human behavior. That might apply when pondering why GMC executives directed the development of the Toro-Flow diesel. Given the array of diesels the GMC truck line had to choose from, most notably those built by GM itself, it seems an odd way to spend money. Well, GMC execs saw a low-cost diesel gap in the medium-duty truck market. Yes, the GM two-strokes were widely available, but they were expensive and noisy. GMC was not averse to going outside the company for an engine, but none of the choices quite met the low-cost criteria either. Introduced in 1964, the Toro-Flow was the answer, but it had some baggage.

The development process for a four-stroke, low-cost diesel began in 1953 and was eventually synchronized with the development of a new 60-degree V6 gasoline engine to be introduced for 1960. This is not to say the diesels would be “converted gas engines.” They weren’t. It’s more accurate to say the gas and diesel V6s were concurrent developments to be built with similar architecture and on similar tooling. There was very little actual parts changeover.

The well-regarded GMC V6 gassers were initially offered in 305, 351 and 401 ci, but by ’62 had grown to 478 ci and later 379 and 432 ci versions were offered. They were one of the first V6 engines offered in the United States, and the 305-powered GMC fleet of light trucks, a deliberate snub of the Bowtie Stovebolt inline. But enough gasser drivel!