Once Upon A Time, GMC Built A V12 Engine For Semi-Trucks

Today, GMC and Chevrolet remain closely aligned on the engineering side of things when it comes to trucks. We may see more of that change with the 2019 Chevrolet Silverado and 2019 GMC Sierra, but decades ago, things were different.

Back in the early 1960s, GMC wanted something monstrous to plop under the hoods of semi trucks, so engineers built an 11.5-liter V12 engine, Driving reported. It’s real, and it provided real big torque numbers for the day. At 2,100 rpm, drivers had access to the massive V12 engine’s 625 pound-feet of torque, though power was rated at just 275 hp. Still, it was a beast.

Amid inexpensive gasoline prices, heavy-duty and semi trucks often utilized gas-powered engines over diesel, which led to the gasoline-fed V12’s birth. GMC didn’t just slap two V6 engines together, however. The brand built a unique block, cam, a special oil pan, and the special crankshaft weighed 181 pounds alone. Total weight of the engine? A portly 1,500 pounds.

The engine never found its way into regular trucks from GMC or Chevrolet, but a Florida-based shop will gladly sell buyers a rebuilt unit. GMC produced only about 5,000 V12 engines between 1960 and 1965, which makes this a pretty special engine.

Former GM Authority staff writer.

Sean Szymkowski

Former GM Authority staff writer.

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  • Nearly guaranteed if GM took 12 Bolt EVs, replaced the EV gear with this V12 and sold them for $120,000/each, they'd sell out the first day they open up dealer allocation...lol

  • Given GM's global parts bin.. one can easily dream about a 4.0-4.5L DOHC-4v V12 with Quad Turbochargers to make 800 horsepower @ 6500 rpm and shoehorned into the 2019 Chevrolet Silverado.

  • Interesting to see is the fact that each carburetor (I think a 2-bbl unit each) drives 6 cylinders only, while I would have expected more carbs. On GM's then high performance engines, the V-8s would be equiped with tri-power units (3 carbs for 8 cylinders). Think of the 1957-1960 Cadillac Eldorado and Pontiac's tri-power units. So I suspect making a lot of power was not on the engineer's list, but rather torque was the goal.
    Other interesting fact is that compressor-alike item on top of the engine: was it meant to be used for air ride? It very much looks like the air suspension compressor used by GM in 1958-1960.
    Nice engine!

  • The story of big gas engines is ending. New electric motors can generate more torque than the average V8 engine, The Tesla Model S is one such example. We now see hybrids using the electric motor as the main propulsion with a small gasoline engine for range extending (as in the Chevy Volt). And the new Chevy Bolt EV has plenty of torque that few gasoline engine can produce at low revolutions. There is a YouTube video of a 2015 Chevy Spark EV out accelerating a 2015 V8 Chevy Camaro at a traffic light!

  • Imagine what that engine would produce with todays technology; i.e. AFM, VVT, DI, computer controlled, etc.

    • Not needed? Chevy performance still sells brand new 290 HP 350 motors for use with a carburetor, someone still buys these. Also available 383, 427, 454, 502, 572. GO to MTU for new Detroit Diesel 2 strokes.

        • True. I see that you can even get new motors for a Cord. Who would have a Cord that needs a new motor?

          • A few years ago there was a local guy with a 810 Cord with a Mopar engine adapted. He needed an engine but could not afford an original.

            Never say never.

            He sold it an I hope some corrected it.

  • Brian these engines are not saved today to race with. Today the street rod guys hue them in hot rods for more interesting engines.

    They do have good power but the weight negates much of it.

    I have seen a hand full of these being used and the are cool in a high boy or such.

    While they did not just slap two V6 engine together they did share som parts with the 366 so it makes them easier to rebuild if found.

    Kim you are going racing there are much cheaper lighter and easier to fit V8 engines that will do the job. But in a open hooded hot rod these win for just being cool.

    • The straight 6 and slant 6 had it's day but they need to go by the waste side also! Flat head engines were kool in some people's eyes back then but now they are pointless!

      Point is that engines need to be put to rest after a certain point

      • Nobody told BMW, Jaguar, and Mercedes that the straight 6 was dead. I'd take a straight 6 in a Silverado, it wouldn't look as goofy as the V6 does with all the space between the motor and rad, it would be smoother too.

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