702 cubic inches

[joehalford01]

Ok, i may have found the answer to my needs.

I just learned about the 702 ci v12 motor that GMC made in the 60's. Info is really scarce out there, I was wondering if anyone here had anything on it? The make about 600 lbs of torque and 250 hp with a rev limit of about 2400. However they are based on the 351 v6. They have a stock compression of 7.5:1. I'm thinking that with a little work and some creative use of available v6 hop-up parts you could get a red-line of 4000rpm and about 800-1000 lbs. of torque. Plus it would fit the era of my truck and be almost the same manufacturer. How crazy am I? How hard is it to find one and if I did could I afford to buy it? I'm hoping I can find an old junky truck with one that someone dosn't want and just buy the whole truck for cheap. Anyways, let me have it.

 

[Tripper]

Someone posted!

Joe,
I think someone may have posted something like that once! I'd say a beefy extended frame would b n order!!! ; - >

BoB

 

[motomech]

here it is but it looks really long its found in alot of heavy trucks like fire trucks

 

[Gastrick]

Joe, when they say based on a 351 V6, they mean the engine is basically two 351 V6's in tandem and is a V-12. The engine itself weighs over 1400 pounds and takes up a lot of space. On the upside, you can get transmission adapters for it that would allow you to run something readily available for a gearbox.

 

[Gastrick]

Oh and by the way, at least one of them has found it's way into a rod. The Blastone Brothers used one in one of their oversized creations.

 

[Tripper]

Allison!

Remember back in the day... there were several cars sporting Allison V-12's. You never see them anymore!

BoB

 

[Gastrick]

Joe, the most important fact to know about these engines is that GMC actually produced plaid valve covers that fit them. . Strange but true.

 

[Bonehead]

Joe, the most important fact to know about these engines is that GMC actually produced plaid valve covers that fit them. . Strange but true.

]

Is there anything you don't have a picture of?

 

[earthman]

awesome. i would like to see someone use an old gmc v12 diesel
with the twin superchargers.

 

[joehalford01]

for a second there i was thinking this might be so obscure you wouldn't have a pic, oh well in firetrucks? i need to start looking. as far as performance, i was thinking performance stuff might be available for the 351's that i can use. i think the weak point is the crank, i'm guessing it's the reason for the low rpm's.

 

[Gastrick]

Joe,

Here's a link for you with plenty of info on these beasts. The reason for the low RPM's is that the engine was designed for trucks that require a lot of torque. Most all engines that produce gobs of torque make all of their power in the lower RPM range. I doubt that the crank is weak, but I'm no expert.

http://6066gmcguy.org/TwinSix.htm

 

[joehalford01]

thanks dude, i did browse that site earlier and will have to go through it some more. i read it was the weakest point because it is so long but define weak .

i think i found something already, too bad i can't buy anything right now

http://cgi.ebay.com/ebaymotors/Freightliner-Double-Bunk-12V71-Detroit-Jake-Nice_W0QQitemZ150153702456QQihZ005QQcategoryZ80760QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

 

[R Pope]

Those engines are dogs. Gutless and thirsy, and a grenade as well. I wouldn't take one as a gift!

 

[Gastrick]

Those engines are dogs. Gutless and thirsy, and a grenade as well. I wouldn't take one as a gift!

So I take it that you don't like them

 

[joehalford01]

Those engines are dogs. Gutless and thirsy, and a grenade as well. I wouldn't take one as a gift!

I am leery as they are made for moving lots of stuff at low speeds, not hot-rodding. But they also came with two two barrel carbs and tiny exhaust. I would think a couple four barrels and decent exhaust would wake one up, especially if you bumped the compression. Kinda hard to know without trying first though i guess. hmmm......

 

[joehalford01]

http://www.youtube.com/results?search_query=702+gmc&search=Search

Dosn't look like it has any trouble moving the fire truck around, I couldn't imagine what it must sound like through headers .

 

[Gastrick]

Is there anything you don't have a picture of?

Yes there is. But I'm not likely to get any either