Craigslist Find: A GMC 702ci V-12 – How Does 585 ft/lbs Of Torque At 1,600 RPM Sound To You?

Craigslist Find: A GMC 702ci V-12 – How Does 585 ft/lbs Of Torque At 1,600 RPM Sound To You?

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?

Craigslist Link: GMC 702ci V-12 

Just for a little inspiration, here’s one being taken to 5,000 RPM, courtesy of

(Thanks to Ron Ward for the tip!)

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5 thoughts on “Craigslist Find: A GMC 702ci V-12 – How Does 585 ft/lbs Of Torque At 1,600 RPM Sound To You?

  1. BeaverMartin

    This engine deserves to be in a Blostolene style roadster. I picture it looking like a large scale old school Indy racer.

  2. 65RHDeer

    So what Tacho can you buy that has a setting for 12 cylinders?

    I think it may be doing closer to 3300 rpm.

  3. Tom P

    There was a car being built at Stave Falls Auto Wrecking in the late 80’s with one. Mid 60’s Pontiac, no idea if it was ever finished but I’ve seen their “prototype” on the road fifty miles away from there. it was a 70’s Ventura ( Nova type) with a GMC V6 that had the valve cover sticking out the hood, a truck granny low 4 speed with a shifter up my the rearview mirror and an 8 lug truck rear end.

  4. Tom P

    The full sized Pontiac was sitting beside the engine stand they had the V12 running on. 1500 lb engine with barely more than 100 hp should be fine for a car, eh?

  5. ratty

    I would have a hard time trying to figure out what to put it in, er, shoehorn it in. Put it in my 84 crew cab dually and make use of that torque, or upgrade the hell out of it and make it work in a race car just for fun? The only problem would be finding a replacement crank or cam should they fail. I don’t know, does anyone even have the ability to custom build something that long?

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