# Does anyone know anything about the GMC V12 motor



## NaeKid (Oct 17, 2008)

A friend sent me some pictures and information about a motor that I have never heard of before, a GMC V12 motor that was originally designed as a stationary engine, but, was put into vehicles ... ya, guys like more power.

I took a moment and made a quick slide-show with the sounds of an actual V12 motor that I found and put it all together






What do you think of this motor and how well do you think it would do for a BOV?

A little more eye-candy ..






Fit it into a BossHoss frame?


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## Tirediron (Jul 12, 2010)

The 12V 702 , a monster of an engine , but thirsty, the key to their longevity was the low horse power and rpm, The twin cap distributors looked awsome, the V6 / V12 engines were only used in US GMC trucks, Canadian GMC s had chevrolet engines.


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## Jimthewagontraveler (Feb 8, 2012)

I worked at the place that got the rebuild contract on those
I remember them all right how could you not.
Beautiful engine yep yep 
Bug out vehicle? Hmm…
I don't know about that.
As a bov I want tough REAL TOUGH.
I seem to remember a problem with very thin sides on the block
Just above the oil pan bolts.
I also seem to recall one of the first ones twisting in half on 
the dyno.
That's when we learned just how carefully you had to torque 
the main caps.
Not totally sure on this part but that may have been the one
that instead of 2 bolts per main cap it had 2 bolts 2 screws
and 4 nuts and needed them all.
Then again that may have been the V10.
I do remember thinking " geez why not just get a lycoming"
I do remember they had to be VERY VERY CLEAN.
The average sb Chevy/ford always had junk flush out at the 
dyno after a total bake off rebuild and we always had a %92-96
success rate on them upon install.
Which doesn't sound all that good but when you have 200 different
valve springs to sort out.
I my self was once guilty of putting v8 timing gears on 20-30 
V6 blocks.
But since the only difference was they were to strong we just
let em roll out the door.
So after some thought no not bov material.
Wait unless your bov flies. Then maybe?


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## LincTex (Apr 1, 2011)

Tirediron said:


> The 12V 702 , a monster of an engine , but thirsty,


Honestly, pretty much worthless and obsolete. Not many good examples left. Horrible power to weight ratio. I can't think of any "practical" use for one.

A good 454 Chevy will do what that thing will do... with less weight, less fuel and do it for a lot longer. If your heart is set on heavy (and truck dedicated), get a 427 from an old school bus. You will be able to tell it by the twin thermostats.


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## Jason (Jul 25, 2009)

I'm no great mechanic, and I've never seen one of thse engines, but it seems to me that the more moving parts you have on a given piece of equipment, the more potential failures you have. Looks and sounds completely badass, kinda like 2 v6's bolted together. But when the SHTF, looking badass is the least of my concerns.

Thanks for sharing about this engine, Naekid. It's a new one on me.


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## LincTex (Apr 1, 2011)

I do like that it makes a lot of torque at low RPM's, but a 6BT-5.9 Cummins will slaughter that thing in all depts: size, weight, torque, and fuel mileage. ...and it is a LOT easier to find used in good condition.


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## BillT (Oct 31, 2011)

I'm familiar with the GMC V-12, but I never drove one. If you like V-6 type power (the 702 V-12 was pretty much 2 351 V-6's put together) check out the 478 V-6. I drove one of those in a '62 GMC 6500. The 478 was the biggest of the V-6's. Plenty of Torque and plently of Power. Not fast off the line and not great on MPG, but you got a lot out of what you put into it. 

Bill


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