Subtle, this monstrous engine isn’t. You will never, ever be subtle with twelve cylinders making power. Not in a Ferrari, not in an Aston Martin, and most certainly not in a GMC Truck. This is the GMC 702ci V-12, an engine used to power large commercial trucks, irrigation systems, the Minuteman ICBM carriers. It’s a stout unit, a specially designed twelve-cylinder block with huge bore spacing for better cooling, a large list of parts that are shared with GMC V6 engines, four heads, four exhaust manifolds, a 180-pound crankshaft, a four gallon oil pan, and enough durability built in that it could run at it’s upper RPM range for weeks on end just fine in certain applications.
This particular Twin Six is up for sale out of Kansas and while it looks rough, appears complete and turns over. Fixed to run on natural gas, there isn’t a fuel pump but we’d be looking to the aftermarket to feed this beast anyways. You’d have to borrow a stout forklift to move this nearly 1,500 pound monster around, but imagine the fun you could have with an engine that makes massive power below 3,000 RPM. Only around 5,000 Twin Sixes were made, and few exist in any useable shape. What can 11.5 liters of workhorse power do for you?
Just for a little inspiration, here’s one being taken to 5,000 RPM, courtesy of ThunderV12.com:
(Thanks to Ron Ward for the tip!)