BY JIM ALLEN
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.
PHOTOS COURTESY OF GM HISTORICAL
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.