Check out this video I found about Big GMC truck engines. Thiers a few hot rods with these odd ball engines in them. Mods delete if O/T but I think most (if not all) were built before '66.
Low speed torque monsters. One of those sixes is heavy enough and two hooked together would be up in the 4 digit weight count. We were pulling GMC V 6 engines out in the 70's and replacing them with V8 engines because they were gas hogs and even then you had a challenge getting parts for them. That V12 got about 2/4 mpg on a good day but would haul a serous load for a gas engine.
A friend of mine Ken C, in Wenatchee, Washington has two GMC V12's, one for part's and the other running in his Old 40's GMC Grain Truck cutt down into an OT build. With around a 16 speed Standard Trans, that's combined with the Two Speed Differential, and Big Duallys. The running GMC V12 (702 ci, If I remember correctly) original came from a Big Farm and used for an Irrigation Pump, from a southern state. It's one cool looking engine and sounds great with open short homemade Header's. Keep On Trucking Brother's...
GMC also produced a 637 ci. V8 that was intended to be a more "economical" replacement for the 702 V12. Basically the 478 V6 with 2 more cylinders grafted on. It still had a 60 deg. V angle , which required a balance shaft to handle some of the odd vibrations. Came in both Gas and Diesel varieties. The gas unit was rated at 275 hp, and 560 ft-lbs of torque. Being that these engines were m***ively over-square (5.125" bore vs. 3.86" stroke), they would probably take well to some hot rodders tricks, ***uming you can keep it from shaking itself apart. The V8 weighed in at just over 1,200 lbs fully dressed, but that was still 300 lbs less than the V12. I have always wanted to take one of these large displacement g***ers from the 60's and early 70's (Ford 534, GMC 637, IH 549, etc), add a nice big turbo or 2, tune it to make peak torque right around 2000 rpms, and put it in a tow rig. Lots of boost, and let the turbos do the work. If done correctly, I think you could embarr*** the hell out of more than a few diesels pulling anything short of a house, and still get "respectable" mileage.
Yes it's Ken Coates from Wenatchee Washington, "The Grafter"... Ken has some cool stuff. Keep On Trucking Brother...
If you want to go down the rabbit hole: Info: https://6066gmcguy.com Forums: https://6066gmcclub.com/
Someone go get it. https://www.purplewave.com/auction/250326/item/ED5514/GMC-Engines_and_Motors-Engine-Texas
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