Facebook Marketplace offers a bizarre mix of items, and today, we’re focusing on a fascinating find: the infamous General Motors “Twin Six” V12 engine, known for its impressive size and power.
Targeted at a niche audience, only about 5,000 units of the Twin Six were manufactured between 1960 and 1965. The exact number of operational or salvageable engines today remains unknown. According to ThunderV12, which provides a modified version of the Twin Six with 425 horsepower, it is estimated that around 200 are still in existence, many of which are described as “basket cases.”
Currently, one engine is being offered for $4,500 in Casper, Wyoming. The seller describes it as being in fair condition, though it lacks a starter. However, it does include a gearbox and transmission. Another unit was sold for $2,900 out of Ohio last year. This seller, who seemed to have lost interest in their V12 project, offered the unit mounted on a mobile stand.
Though the Twin Six’s production was brief, it gained a following for its impressive specifications, size, and rarity. Unlike merely combining two 351ci V6 engines, the Twin Six featured a robust, single-piece iron crankcase measuring four feet in length and weighing 190 pounds. This 11.5-liter V12 was equipped with four cylinder heads, four exhaust manifolds, two distributors, two intake manifolds, an oil sump with a four-gallon capacity, and a high-volume oil pump that circulated 17 gallons.
This entire assembly weighed in at 1,485 pounds—on par with many small cars of its time—before safety features and smartphone connectivity became industry standards. Despite its sheer size, the V12 engine produced only 275 horsepower at 2,400 rpm, which might not seem impressive by today’s standards. It was originally intended as a diesel substitute for industries demanding heavy-duty engines, such as agriculture, emergency services, military, and trucking, where torque is critical. The GM Twin Six delivered a hefty 630 pound-feet of torque between 1,600 and 1,900 rpm, enabling it to tow up to 60,000 pounds up steep inclines—all while running on standard 87 octane fuel.
The seller in Wyoming posits that around 1,500 Twin Six engines are still around today. While a definitive number may always be elusive, it’s likely that any units coming to market are aimed at long-term project builds. For the right enthusiast, investing in restoring one of these rare engines might be worth the price of admission for this automotive legend.
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