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GMC "Big Block" V6 and 702 "Twin-Six"


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#1 1972coronet

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Posted 09 December 2012 - 05:31 AM

I've always been fascinated by the GMC V6's (305/351c.i.d.) and the truly odd Twin-Six (702 c.i.d.) , and am wondering if anyone makes one or both of these neat looking engines in 25th scale .

 

I'd like to build the Tom Daniel's "S'Cool Bus" with a Twin-Six in-place of the kit's engines ; I'd like to add a couple of 6-71 blowers atop as well .

 

Also , if anyone's made their own 305/351 or 702 Twin-Six out of scratch materials or modified from an existing kits' engines , please feel free to post pics of them here :) .



#2 charlie8575

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Posted 09 December 2012 - 05:17 PM

The V6 was a cut-down 348, and I'd imagine the 351 was a cut-down 409, so you might be able to cobble up something using a spare W-Motor.

 

Charlie Larkin



#3 1972coronet

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Posted 10 December 2012 - 03:38 AM

The V6 was a cut-down 348, and I'd imagine the 351 was a cut-down 409, so you might be able to cobble up something using a spare W-Motor.

 

Charlie Larkin

Hmm ... sounds like a plan . I thought that those engines looked like chopped W-Engines , but had no idea that they were based upon the tooling of the 348 (ad seq.).



#4 Longbox55

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Posted 10 December 2012 - 05:12 PM

The V6 was a cut-down 348, and I'd imagine the 351 was a cut-down 409, so you might be able to cobble up something using a spare W-Motor.

 

Charlie Larkin

The GMC V6 shares no parts with the W engine. It was not a "cut down" 348 or 409. In fact, the V6 actually dwarfs the W engine, and even the Mark IV engine that came after it, being a few inches longer and taller, as well as weighing in at around the 800 pound mark, dry. The block is a 60 degree Y block, with a deep skirt at the bottom of the block, unlike the Chevrolet engine, which is a 90 degree block with no skirt. There V6 came in 305, 351, 401, and 478 ci displacements, plus the was a 637 cid V8 based on the same block in addition to the 702 cid V12. The 351 and 478 V6 and the 637 V8 blocks also saw use as Deisels, using the same block with different pistons, heads, and intakes.

Jolly Goodfellow's site is probably the best reference source for these engines. http://www.6066gmcguy.org/gmcv6a.htm



#5 landman

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Posted 24 July 2014 - 02:04 AM

Here's a 702. This one was on the back of a 40's REO at a car show. The company I used to work for had several in float tractors. They were mated to 20 speed 5/4 transmissions.



GMCV-12.jpg

#6 plowboy

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Posted 24 July 2014 - 04:31 AM

There used to be a personal junkyard about a half mile from my parents' house. It had a late '40s early '50s GMC truck setting in it among several others. It had the V-6 engine in it and to me, it looked kinda like a big block with the two rear cylinders lopped off. I wish it was still there or I had taken photos of it. It along with the rest got buried. The saddest part was one of them was a 409 powered '63 Impala.  



#7 1972coronet

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Posted 26 July 2014 - 01:27 PM

GMCV-12.jpg

 

Nice Twin-Six , Pat !



#8 unclescott58

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Posted 26 July 2014 - 03:48 PM

The V6 was a cut-down 348, and I'd imagine the 351 was a cut-down 409, so you might be able to cobble up something using a spare W-Motor.
 
Charlie Larkin


This type of info drives me nuts. Mr. Burmeister beat me to the punch on this one. Everything he said about the GMC motor is correct. By the way, look at were the spark plugs are on the GMC V6s. This is no Chevy W-Motor. Not even close.

Scott

#9 Longbox55

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Posted 27 July 2014 - 11:10 AM

There used to be a personal junkyard about a half mile from my parents' house. It had a late '40s early '50s GMC truck setting in it among several others. It had the V-6 engine in it and to me, it looked kinda like a big block with the two rear cylinders lopped off. I wish it was still there or I had taken photos of it. It along with the rest got buried. The saddest part was one of them was a 409 powered '63 Impala.  

Most likely, what you saw was a '60-'74 GMC. 



#10 Superpeterbilt

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Posted 28 July 2014 - 01:07 AM

Thanks for this info guys! I knew nothing of these engines. Now Im gonna have to build one.....

#11 landman

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Posted 21 August 2014 - 01:27 AM

 

 

Nice Twin-Six , Pat !

That's not a model, that is 1:1. 



#12 plowboy

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Posted 21 August 2014 - 07:40 AM

Most likely, what you saw was a '60-'74 GMC. 

 

The pickup was definitely a '48 or '49 five window. They had a early '60s GMC that was totaled. So, more than likely, that was where the engine came from. The next time I see the owner, I'll have to get the story from him on that old truck. My brother may know. His first car actually came from their junkyard. It was '60 Falcon with a blown engine. 



#13 Tarkmucker

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Posted 23 September 2014 - 09:04 PM

Does anybody know if a kit has ever been made with this engine?

#14 chunkypeanutbutter

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Posted 24 September 2014 - 05:20 AM

Find a kit that has the six cylinder it's based on and splice em together. Not sure if it was ever kitted as V12, maybe someone else knows.

#15 1972coronet

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Posted 24 September 2014 - 02:00 PM

I'm not even certain that any of the GMC "big block" V6 engines ( 305 , ad seq. ) were ever produced in-scale , let alone the "Twin-Six" .

I've been wanting to plunk a Jimmy'ed GMC V6 into a Street Rod !



#16 Longbox55

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Posted 24 September 2014 - 03:59 PM

Unfortunately, none of the GMC 60 degree V6, V8, or V12 engines from the '60s were done in scale.



#17 Chuck Most

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Posted 24 September 2014 - 04:52 PM

Are there any existing kit-based V-Engine blocks that would be close in size? If there were, you could just kitbash and scratchbuild from there.



#18 Longbox55

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Posted 24 September 2014 - 05:13 PM

None that I'm aware of. Those engines were real monsters compared to the typical V engines of their time, the V6 even dwarfs the big block V8s found in most other vehicles of the time. There really wasn't any parts that swapped with other GM V engines, either. It was a clean slate design, not used in any other GM road vehicles, other than a few models of HD Chevrolet truck as an option.



#19 1972coronet

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Posted 24 September 2014 - 05:53 PM

*Maybe* a Chevrolet 'W' engine could be used as the basis . The rocker covers and  heads are close ; probably a cut-and-invert would work .

I believe that the spark plugs are on the intake-side of the ports ? Ignition distributor on the rear of the block , sticking straight-back ?

 

As a side note ; the early engines' biggest handicap was its atomiser : a tiny , single-pot carb !

 

I think that a 305 (ad seq.) would look sweet with a 4v71 Jimmy sitting-atop .


Edited by 1972coronet, 24 September 2014 - 05:55 PM.


#20 1972coronet

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Posted 24 September 2014 - 05:56 PM

How about a Toro-Flow GMC diesel ? ;)