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Custom 1964 GMC Truck with a Twin-Six V12

Custom 1964 GMC Truck Rap'em Pappy with a GMC 702 ci Twin Six V12

This 1964 GMC truck was built by Robert Wunderlin in Wisconsin as a tribute to the B24 Liberator crew Rap’em Pappy who went down in Germany during WWII. The truck’s frame and front body panels were extended to hold a very unique power plant.

Custom 1964 GMC Truck Rap'em Pappy with a GMC 702 ci Twin Six V12

Powering the truck is the 702 ci (11.5 L) V12 called the “Twin-Six”. The engine appears to be two separate V6 engines welded together but it uses a single cast block and runs a single long cam and crankshaft. Everything about this engine is big. It uses 16 quarts of oil, 72 quarts of coolant, weighs 1,485 lb, the crank alone weighs 180 lb, and produces 650 ft-lb of torque at 1,600 rpm. Since this engine was built for torque, 250 horsepower at 2,400 rpm is the most it ever produced.

The engine was built by GMC for commercial trucks to provide large torque but also be very affordable to service since a majority of the parts were interchangeable with 351 V6 parts such as the four heads and four exhaust manifolds. You can read more about the engine at Engine Labs. If you are interested in running one of these in your own hot rod, Thunder V12 sells a turn-key engine for $18,000.

Source: ScottieDTV, 6066GMCGuy and photos from 67-72ChevyTrucks

14 thoughts on “Custom 1964 GMC Truck with a Twin-Six V12”

  1. That is one bad ass engine man I love it,the ppl who made the Bugatti did the same thing to there car they put two big v8’s together an called it the w16

      1. I see. But the linked article says it’s a 1962 GMC. The article of the restored GMC (above) says it’s a 1964. I am assuming that you are the author. I’m not complaining at all. I just thought the info would be helpful for those who’d like to know. Including the both of us.

        1. I appreciate your help but there are multiple projects in the article. The 1962 GMC called “1962 GMC V12 Twin-Six 1 Ton” is a different project than the one mentioned in our article. It is has a flat bed and is painted a light brown color. The info on the 1964 GMC truck called “1964 GMC V12 Twin-Six Rap’em Pappy” is right below that project in the 6066gmcguy article.

          1. Thank you, swaptastic. I understand. The thing is that I’ve been in contact with your source ScottieDTV and he doesn’t know what year the “GMC V12 Twin-Six Rap’em Pappy” is. So, now I’m curious to know if you actually quoted him as stating it’s a 1964 or if that part is your own personal guess? If I understand it right, neither you nor ScottieDTV know what year the truck is. Yes?

            1. You are correct. I do not know for certainty what year the truck is. I based the year off the website I included in the previous comment. It contained the most detailed information I could find of the project.

    1. I think you misunderstand me. You based your article on information you found from ScottieDTV. Your link shows (1) a 1961 GMC and (2) your own article stating it’s a 1964. There is no more detailed information than that. Now, if ScottieDTV said it’s a 1964 then I understand where you got it from.

      Chilton Books used to have drawings in the beginning of the book showing all of the front ends and back ends of all every model of that make so you could see the tiny changes and determine the exact year. I don’t live in the U.S. so I have no possibility of finding one for the 1960 – 1966 GMC trucks. Maybe you could find one? Or …. probably I’ve been beating a dead horse and nobody really cares anyway. LOL! If that’s the case then just forget it and have a nice day! 🙂

      1. I based my information from Scottie’s video and this link That site is dedicated to GMC trucks so if they say the project was a 1964 then I have no reason to say otherwise. If you can direct me to any website or photo that shows evidence this truck is another year I would gladly update the article. I do care about getting information in my articles correct and I welcome any proof you can offer.

          1. My comments have to do with cars and engine swaps. Your comment doesn’t seem to have anything to do with either cars or engine swaps. Maybe you made a typographical error or are you just trying to give me a hard time …..

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