Q: Hi, Greg, and if you answer this question, thanks in advance. My friends and I, (all retired and mostly computer illiterate) have been discussing V-6 truck engines, and I absolutely remember a GMC V-12 cylinder engine that was available in 1960 in big trucks. Can you please tell us about this engine, and that there definitely was a V-12 available? Thanks much, we read your column in Auto Roundup every week here in Pennsylvania at our local coffee shop. Sincerely, Charles S. happily retired and born in 1942.
A: Charles, I’d be happy to help. You are correct that in 1960, GMC Trucks designed and made available a unique V-12 engine that comprised of two V-6 GMC engines united by a single engine block and one really long crankshaft. Other than that, the engine comprised of most of the main parts of two 351-inch V-6 engines that appeared that year for use in pickups and heavy duty trucks.
Noteworthy is that GMC was the first manufacturer to offer a V-6 in the truck line (pickups included) and it used its 351-inch V-6 design for its new V-12 engine.
The V-12 was available through 1965 in the heavy duty truck line (see advertisement attached) and topped out at 702 cubic inches (two times 351) of brute strength and torque. The engine was officially called the “Twin Six V-12” by the marketing department. The engine developed 275 horsepower and 630 lb. ft. of torque from 1600 to 1900 rpm, and was able to climb hills better than a diesel engine with minimal downshifting according to reports from General Motors.
Notable is that even today, both Volkswagen and Audi have released similar ideology engines, as both of their 12-cylinder models apply similar thought. However, the major difference between GMC in the 1960s and VW/Audi today is that Volkswagen (with its Phaeton) and Audi (with its Audi W12) mount its V-6 engines side by side in a “W” design attached to a common crankcase instead of lengthwise. Thus, even though it looks like GMC’s V-12 is two mated V-6 engines, in reality it is not so thanks to the shared single block and four-foot long crankshaft.
Today, the chances of finding one in a wrecking yard is next to impossible as enthusiasts have scoffed them up and rebuilt them. If you can get someone with a computer to show you, one of the nation’s top rebuilders and developers of the GMC V-12, namely www.thunderv12.com, has a website I know you’ll enjoy. It’s loaded with interesting history on this many times forgotten GMC engine, along with photos and info galore.
They rebuild these engines to modern day specifications, using quality parts throughout, an improved oiling and cooling systems, modern ignition systems and even use ARP Rod Bolts and Fasteners, the latter the top name in the aftermarket performance industry connecting rod bolts, engine fasteners and cylinder block studs.
GMC heralded its V-12 back then as an engine that would easily run over 200,000 miles, which at that time was usually reserved for the ultimate of semi and tractor trailer type diesel engines instead of a GMC-built gasoline V-12.
Thanks for your letter, Charles, and best wishes to you and your friends.