eBay Find: This Massive GMC Twin Six V12 Won’t Get You There Quickly But At Least It’s Thirsty


eBay Find: This Massive GMC Twin Six V12 Won’t Get You There Quickly But At Least It’s Thirsty

With the story we ran today about the V12 LS engine it seemed only fair that we give one of the more freakish engines that GM ever built its time in the sun. Thankfully there is one of these babies for sale on eBay so rather than just blather at you about the GMC Twin Six V12 we can tell you to buy one! This particular engine has lived in a collection of engines and is in damned fine shape, outwardly anyway. According to the seller the mill was regularly started and run during its time on display and it has been on this run stand for a long, long time. It runs now and can fire with the addition of a little fuel to the carbs which is a good thing.

The seller scored the engine for use in a rat rod and then he got the thing home and decided that it wasn’t something he was actually going to be able to make work so now it is for sale. The engines were used in trucks of various shapes and sizes for years by GMC in an era when the mighty turbodiesel engine as we know it today had not yet come to exist in its current form. This massive 702cu lump of iron made 250hp and 565 lb/ft of torque on a sunny day. The engine is NOT two V6 engines attached or welded together. It is actually a one piece casting. Yes, it does share many of the same parts as the V6 engines GMC was producing at the time but there are some unique properties as well. The twin distributor drive, the four exhaust manifolds and some other specific parts are Twin Six pieces but other than that, the guts are much the same as this engine’s smaller, still low revving cousin. The crankshaft is a one piece unit that weighs nearly 200lbs.

The engine has 56 head bolts, the insanely heave reciprocating assembly is so because of stuff like wrist pins that are over an inch in diameter, and the insane water pump moves 118 gallons per hour to keep the thing cool. This was a heavy duty engine that could run for hundreds of thousands of miles without much service. No one can say for sure how nice the guts of this one are but if you are looking for the cure for the common power plant in your hot rod, this dude has the ticket. Oh, and they only made a couple thousand of them so the chances of being shown up at a cruise night are virtually none.

eBay Link: Here’s a good looking and fine running GMC Twin Six V12 for sale 


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7 thoughts on “eBay Find: This Massive GMC Twin Six V12 Won’t Get You There Quickly But At Least It’s Thirsty

  1. KCR

    Years ago I was driving a dump truck . And I was able to get it really bad stuck one day . A guy shows up to tow me out of the mud I was stuck in, with a GMC cab over tow truck. My truck was loaded with a full load of sand, and down to the frame rails. I was just a punk ass kid, I was asking a lot of questions. All he said was just stand back I’ll get it kid. And just off idle it pulled so hard that it bent a leaf spring on the dump truck I was driving. It dog tracked pretty good after that day. unbelievable torque from a gas motor. And for all you little leaguers out there remember. horse power sells cars ,torque wins the race

  2. BeaverMartin

    I have always wanted to see an Engine Masters style all out build of one of these odd ball beast. Custom billet crank, hogged out heads, sheet metal tunnel ram. It would be sweet.

    1. GeorgeA

      There are people who have boosted the bejesus out of these things for Bonneville and whatnot. Lots of homemade stuff is required since you can’t just call up Jegs and do a credit card upgrade.. Engine sorcery at its finest.

  3. J Curles

    Ford built a huge gas engine back in day, it was primarily used in big trucks and on industrial applications like back up water pumps when the electricity went out. I can’t remember the cubic inches but I do remember helping rebuild one at a manicipality I worked for, and remember the cylinders in the block were big as a coffee can.

  4. Bobby

    In the early 1960’s, my uncle owned a lumber company that had a huge Towmotor brand forklift that sported this engine. They were always having trouble keeping it timed correctly, making it hard to start. One morning, the driver had the air filter off one of the carburetors on it, trying to get it started, and it backfired, caught fire and burned his entire building with Office, showroom and lumber, paint storage to the ground. The old forklift sat where it was parked, all blackened, as the centerpiece of the rest of the enterprise that was in ashes.

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