GM 702 V12

"HammerheadFistpunch" (hammerheadfistpunch) 01/21/2016 at 18:24 • Filed to: engines.

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Just a reminder that GM once made a 702 cubic inch V12 for use in heavy trucks. Thats 11.5 liters. Based loosely off of the 351 V6 design these super heavy (between 1100-1400 lb) monsters were the top dog in heavy duty gas truck engines from semis to nuclear missile trucks

(This one is at Hill AFB near me, I guess I need to go see it especially since my father worked on the minuteman program)

From the factory they produced just 275 hp in top spec (@2400 rpm) but 630 lbs-ft of torque from practically Idle (1600 rpm). They are pretty stout (200,000 miles between overhauls) and with a little massaging from !!!error: Indecipherable SUB-paragraph formatting!!! (yes, you can buy rebuilt and upgraded engines) they can be made to spin up to 4200 rpm were they will be making 425 hp and many torques.

Oh and they bolt up to quite a few transmissions, manual or automatic.

I know I’m not the first person to rave about these engines, but I just re-remembered them and wanted you all to know how amazing I think they are.

Dash-doorhandle-6 cyl none the richer > HammerheadFistpunch 01/21/2016 at 18:32

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Cant find a pic, but the Ford Seamaster/Super Duty engine is along these lines too

RamblinRover Luxury-Yacht > HammerheadFistpunch 01/21/2016 at 18:36

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Okay, bear with me: somebody needs to determine the coolant passage setup on these. Why? Because there was a 478 on the same plan, and if the twin-six block will bear increase to that larger bore (5.125!!), then even remaining on the stock crank and not increasing, you’d have an 886. If you could get a madman to cast you a special crank, you’d have a 956. A 15.7 liter engine.

Jordan and the Slowrunner, Boomer Intensifies > Dash-doorhandle-6 cyl none the richer 01/21/2016 at 18:40

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I think they were pretty close in displacement, but it was only a V8.

they-will-know-my-velocity > RamblinRover Luxury-Yacht 01/21/2016 at 18:41

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You maniac

RamblinRover Luxury-Yacht > they-will-know-my-velocity 01/21/2016 at 18:45

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The way I see it, you could go with a 572 crate, but why settle when something so epically bonzo is on the table? Probably not that much more to get accomplished, either. Two donor 478s for heads,pistons, balance shafts, etc., a 702 for most of the rest.

Jordan and the Slowrunner, Boomer Intensifies > Dash-doorhandle-6 cyl none the richer 01/21/2016 at 18:45

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Further searching reveals that the Super Duty was 534 ci, but it lasted 500k miles between rebuilds.

HammerheadFistpunch > RamblinRover Luxury-Yacht 01/21/2016 at 18:50

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they-will-know-my-velocity > RamblinRover Luxury-Yacht 01/21/2016 at 18:50

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And we can put it in...

A Dodge power wagon! THE ULTIMATE LS SWAP. kind of.

Dash-doorhandle-6 cyl none the richer > Jordan and the Slowrunner, Boomer Intensifies 01/21/2016 at 18:51

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The seamaster was a twin turbo marine version, think I saw it on Jalopnik.

Jordan and the Slowrunner, Boomer Intensifies > Dash-doorhandle-6 cyl none the richer 01/21/2016 at 18:54

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That is pretty cool, but I think I’d rather have a massive V12.

RamblinRover Luxury-Yacht > they-will-know-my-velocity 01/21/2016 at 18:58

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Dodge WC Command Car replica:

lolPaint

Dash-doorhandle-6 cyl none the richer > Jordan and the Slowrunner, Boomer Intensifies 01/21/2016 at 19:03

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Me Too, this is of the more sporting variety:

RamblinRover Luxury-Yacht > HammerheadFistpunch 01/21/2016 at 19:07

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Okay, it gets better. There’s the space in the engine for an eighth of offset grind on the Frank, I mean the crank, in total safety. Even that little gets you the extra 44ci to break ONE THOUSAND CUBIC INCHES.

McMike > HammerheadFistpunch 01/21/2016 at 19:18

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since my father worked on the minuteman program

My father was a career missileer. What did pappa HammerheadFistpunch do?

HammerheadFistpunch > McMike 01/21/2016 at 19:24

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My dad worked at ATK / Hercules during the Minuteman reconditioning program

McMike > HammerheadFistpunch 01/21/2016 at 19:34

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What did they do to the Minuteman? Was that when they dropped the warheads to one?

edit - it was the solid fuel stages, right?

HammerheadFistpunch > McMike 01/21/2016 at 20:02

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Solid fuel, correct.

gmctavish needs more space > HammerheadFistpunch 01/21/2016 at 20:31

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I love the twin six and the massive V6s they used to make. I keep for looking for an old truck that has one in it to be some sort of project....there’s some dude who has a really good running 478 in a pickup.

The Crazy Kanuck; RIP Oppositelock > HammerheadFistpunch 01/21/2016 at 20:32

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It was actually GMC, the 702 Twin-Six V12 was part of the 60° V6 family. The V6 sizes where: 302ci/5L, 351ci/5.7L, 379ci/6.2L, 401ci/6.5L, 432ci/7L, 478ci/7.8L. The 702ci/11.5L Twin-Six V12 was based on 2 351's, but it was 1 casting. It was mistaken as two V6 engines welded together, but it is its own separate engine design based on a single casting. It used four separate exhausts manifold, two separate carburetors, two separate distributer caps driven by a single distributor drive, and other parts from the 351. 56 major parts are interchangeable between the Twin-Six and the other GMC V-6 engines to provide greater parts availability and standardization.

HammerheadFistpunch > The Crazy Kanuck; RIP Oppositelock 01/21/2016 at 20:53

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I have been meaning to put that C up there. Sounds like you’ve also been to v12thunder

Dash-doorhandle-6 cyl none the richer > RamblinRover Luxury-Yacht 01/21/2016 at 21:26

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........(Tim Allen can be heard grunting in the distance).......

vicariousILive > McMike 01/21/2016 at 21:29

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What Wing(s) was your dad stationed at?

Iheartmy365kHonda - Car enthusiasts do like FWD > HammerheadFistpunch 01/21/2016 at 21:34

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How do you even connect two engines together?

HammerheadFistpunch > Iheartmy365kHonda - Car enthusiasts do like FWD 01/21/2016 at 21:40

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You don’t, it’s a single cast block

Iheartmy365kHonda - Car enthusiasts do like FWD > HammerheadFistpunch 01/21/2016 at 21:44

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LOL wut? That’s insane!

McMike > vicariousILive 01/22/2016 at 05:18

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Only two wings. He started in Malmstrom, then spent probably 9 years between Offutt/Pentagon before returning to field at Minot.

Oddly enough, those are the only two wings that remain today.

TylerLinner > RamblinRover Luxury-Yacht 01/22/2016 at 09:51

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All there’s left to do is test fit it in the back of a ‘62 Suburban.

vicariousILive > McMike 01/22/2016 at 13:23

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Don’t forget FE Warren in Cheyenne

That is the only wing I have ever been to. I support ICBM stuff in my job

McMike > vicariousILive 01/22/2016 at 14:00

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Shit, I did forget about the Mighty Ninety. There are so ICBM bases these days, that I thought were were more than two.

The Mighty Ninety actually won the “best overall operations support squadron with an ICBM mission” trophy that may or may not have a “Mc” in its name in 2013.

DrJohannVegas > HammerheadFistpunch 01/22/2016 at 18:34

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One small point: 425HP @ 4200RPM means 531 lb-ft of torque. (Because maths/units.) That is some, but not necessarily “many”.

HammerheadFistpunch > DrJohannVegas 01/22/2016 at 19:10

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That’s many in my book

vicariousILive > McMike 01/22/2016 at 22:32

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My boss(well boss’s boss) was the commander of FE Warren during that whole Taiwan fiasco. He had to go to the secretary of the AF or the chief of staff and got a letter of reprimand. He had nothing to do with it but he still had to take the blame.