V12 engines on the custom stage: GMC

So, we looked at the German and British twelve-cylinder engines, which are quite popular in the hot rodding and custom automotive industry, but now I suggest we return to the US. The main competitor for the Lincoln-Zephyr in its homeland is the GMC Twin-Six 702 engine. This is an extremely unusual engine: externally it looks like two V6s connected together, but in fact it is a real V12: one block, one crankshaft, one camshaft. Unlike the Lincoln-Zephyr engine, the GMC unit is reliable, durable and produces 275 horsepower as standard – a little more than two times more than the old man from the blue ovals. In addition, the Twin-Six was produced from 1960 to 1965, while the last Lincoln-Zephyr V12 was released in 1948.

Cons? They mainly consist in size. And it’s not that the volume of a twelve-cylinder GMC is 11.5 liters – sometimes even extremely large engines may not take up much space. But this does not apply to the Twin-Six: the company designed the engine for the largest trucks of its brand, and therefore no one limited himself to the size when developing the engine. Therefore, the Twin-Six is massive, and everything related to it is no less massive.

This red monster uses 15 liters of oil and 68 liters of coolant, and its weight is 673.5 kilograms, 81.6 of which is only the crankshaft. Also, a certain disadvantage can be noted the rarity of the engine itself: only about five thousand copies were produced, of which only a few hundred have survived to this day. It is difficult to say exactly how many hundreds; basically, this figure depends on the degree of optimism of the expert. This disadvantage is somewhat offset by the fact that most of the parts are no different from those on V6 engines, which are much more widespread.

Fan work

And despite the small number of GMC V12s, there are enthusiasts in America who devote themselves entirely to this particular engine. There is at least one workshop specializing in these monstrous units, the ThunderV12. The Twin-Six, as standard, “just turn the key” from these guys, costs $18,590 today. You can get acquainted with their work using the example of this hot rod.:

It was assembled by Ron Devall, who for a long time dreamed of assembling a car, mostly consisting of General Motors of the last century. He had been collecting spare parts for several years, and as a result, the GMC 35 cabin and the GMC L7000 62 dashboard ended up on the same frame as the rear of the 47, all powered by the aforementioned 1961 700R4 automatic transmission engine. Of course, not all the details ended up being from GMC: the headlights on this car are from Buick 37th, and the turn signals once belonged to a Chevy sedan 40th. The front wheels are from a 1938 Farmall tractor. However, the biggest and most important part of the car is, as Ron intended, from GMC.

Rap’em Pappy: Bomber and Pickup Truck

And now evaluate a slightly less classic project in the form of a 1964 GMC pickup truck called Rap’em Pappy. It is named after the crew of the B-24 Liberator bomber of the same name, which fought in World War II. In 1944, Rap’em Pappy was shot down while flying a mission over Bernberg in Germany. Half of the crew died, and the remaining half were captured. The team had to complete three out of twenty-five missions, after which they would go home.

And in memory of this small piece of World War II history, Robert Vanderlyn built this custom. Bombers are usually very large aircraft, which is why Robert chose a GMC pickup truck for his project, which had a huge Twin-Six engine installed. To fit the engine under the hood, the frame and front body panels had to be extended. In the photos below, you can see that the Rap’em Pappy once had a closed hood and other rims, as well as its exhaust pipes were changed several times, and over time, several pleasant-looking details were added.

The latest version of the pickup truck can be viewed in full detail in the video below. The extremely beautiful interior deserves special praise with a couple of touches referring to aviation: the gearbox lever and toggle switches on the central panel look extremely organic.

The rat from the fire station

Have you ever wondered what happens to old company cars? The answer, in fact, is outrageously simple: they take off all the equipment and either sell it at auctions, or send it to work to the last in other places that are less demanding on technology.

However, the fate of this 1946 Seagrave fire truck turned out to be very out of the ordinary: most of its body and frame were sawn off, and all that remained was reassembled into a very unusual rat rod. The Twin-Six engine for this project was not chosen by chance: the original Seagrave engines were also V-twin engines, and the largest of them were even larger in volume than the GMC engine (namely, 14.85 liters or 906 cubic inches).

Therefore, the new engine fell into place without any problems. The engine also got new Rochester carburettors and a fresh ignition system, but no special changes were made. And in addition to the GMC engine, an Eaton Fuller five-speed transmission and a custom driveshaft were installed.

This car first appeared on the Internet in 2013, and then, five years later, it was put up for auction again. In the photos below, you can see that the new owner has made minor cosmetic changes, embellished the interior and put the engine in order (at least externally), but, in general, it’s still the same rat rod. In addition, I have attached a photo of the original Seagrave 46 so that you can estimate how much was sawn off from the cabin.

“It’s impossible to drive. There are no power steering systems. The brakes are completely mechanical. Loud enough to hurt my ears. It’s very hot in the cabin – there’s no firewall. The huge Eaton transmission is difficult to shift. Gasoline is a complete nightmare. Why would anyone want a car like this? Because it’s the coolest on this planet and it’s incredibly fun!” – this is how the first owner and, apparently, the builder of this miracle describes his experience.

The auction text also mentions the fact that the speedometer does not work (all the instruments are new, only the original panel), but despite all of the above, the car was used by the first owner almost constantly. In the attached video below, you can see a lot of interesting things: from burning out in an empty parking lot to the original, much more worn interior in all its details.

Here are some quotes for you:
“The seats are kind of dirty because I often ride in it, but, um… and I’m usually dirty, but the seats are new…”
“There are 39-inch Mickey Thompson’s in the back. They will scroll mercilessly even when starting in third gear.”
“Maybe someone will make it a little more beautiful, or maybe someone will like it the way it is.”

And that’s probably all I wanted to tell you about GMC Twin-Six cars. There is another hot rod with a monster engine, but it is a real star, so I decided to dedicate a separate article to it. As for our collection of monsters with V12 engines, there are only two parts left, in which you will find engines even more voluminous, unusual and rare than the Twin-Six.

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