TORO-FLOW: THE OTHER GM DIESEL
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!
The Toro-flow diesels debuted in 1964 in two displacements, 351 ci (the D351, 130 hp) and 478 ci (D478, 150 hp). A high-output model was also offered, the DH478, cranking out 170 hp. It’s been reported that GMC toyed with the idea of a diesel 305 V6 in the light trucks but it isn’t clear how far the idea went. Probably
A fully dressed D478 V6 from a 1964 show where the engine was first being introduced. Note the twin air filters. The air filter arrangement varied from these twins to ducted, centrally mounted filters, depending on underhood clearance. The GMC orange paint is seen on many ’64 and ’65 engines but gradually seems to change to yellow after that.