The mother of all engines, the GMC Twin-Six V12 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

texanidiot25 · 10-31-2007, 05:19 PM

I love the thought process you had to have for this motor back in the day:

"So today, we need to make an engine with loads of torq-"

"Lets stick two of our small-block V6s together with bullet proof parts!!!"

"Brilliant!"

It was featured on Jalopnik.com as the Ass-Kickin' Engine of the Day

Quote:

Ass-Kickin' Engine of the Day: GMC Twin-Six V12

After doing a little research on the GMC V6 in today's DOTS car (and recalling a reference to the Twin Six by commenter Paul_Y a while back), I find it necessary to pay homage to the mighty GMC Twin-Six engine. It wasn't two GMC V6s joined together- it had a unique block and crank, with four V6 cylinder heads bolted on. We're a little puzzled about why you'd use a gigantic gasoline engine for applications so obviously suited for a diesel, but who the hell cares? Look at this thing! Jump like a Twin-Six-equipped Suburban cresting a hill for more info...

http://jalopnik.com/cars/engine/ass+...v12-315982.php

Found more info at http://www.6066gmcguy.org/TwinSix.htm
http://www.6066gmcguy.org/Jolly-702v12.htm

Quote:

This is the king of GMC's gasoline engine family, the power-laden 702 Twin-Six. It makes words like durability, performance and operating economy take on a whole new meaning. It's true truck horsepower and tremendous torque at low r.p.m. take on the biggest jobs with an easy-stroking effort. It digs into grades and requires far less gear shifting to keep in step.

With relatively slow operating speed, of only 2400 maximum r.p.m., the Twin-Six combines ideal fuel / air mixture, economical 2-barrel carburetion, low internal friction, short stroke, and good exhaust scavenging to add years to engine life and squeeze every mile from every gallon of gasoline.

It made 275hp @ 2400 rpm, and 630 ft lb or torque @ 1600-1900 rpm

Please tell me someone here has one

**WorkinLonghorn** · 10-31-2007, 05:37 PM

I have two.....on my spec sheet that's been kicking around for 20 years. Pretty cool. I always wondered what they looked like.

NONHOG · 10-31-2007, 05:50 PM

Please tell me someone here has one[/QUOTE]

Check "cayoterun" see his posts , he has lots of pics ! GMC V-12 powered '91 Chev crewcab ( 1 2 3 4)

texanidiot25 · 10-31-2007, 05:52 PM

Sure will.

I really want to hear this thing too... but I cant find any video.

cayoterun · 10-31-2007, 07:20 PM

Hello--

Hope to submit a video, with sound, before tooo long,but as posted, project posponed due to family illness.
Last pic posted is where we are. It shouldn't be too far from running when we can get back to work.
Join us with this project, and give your ideas.
Thanks
Cayoterun
Oh, save a post. What's the wheelbase on a 1ton Xcab- late 80s, early 90s???

Longhorn Man · 10-31-2007, 08:38 PM

someone had a photo of one in front of a junk yard.

724x4a/cchevy · 10-31-2007, 08:53 PM

Here ya go longhorn. Pretty sure this is the one you are talking about.
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67_C-30 · 10-31-2007, 09:23 PM

I have a coiuple of 305 V6's and a 351 Magnum V6, but no V12's. I don't what the hell I'd do with it, but I'd love to have one!! Here's some more pics, ads and drawings. A bad crank out of one of these would make a killer mailbox post wouldn't it??

67_C-30 · 10-31-2007, 09:27 PM

Oh, I almost! The coolest GMC V-12 powered vehicle on Earth!!! The B-702!

67_C-30 · 10-31-2007, 09:29 PM

Then there's Frankenstein!!

Stepside65 · 10-31-2007, 09:54 PM

Gotta love the giant motor.

Longhorn Man · 10-31-2007, 09:56 PM

Yep... that's the one!

Quote:

Originally Posted by 724x4a/cchevy

Here ya go longhorn. Pretty sure this is the one you are talking about...

**special-K** · 10-31-2007, 10:28 PM

I was gonna say the 702 would be awesome in a rat rod.Talk about funky obscure.

Hoods69BadBowTie · 10-31-2007, 11:03 PM

Wow thats pretty kool. Not very burly motor but defiantly unique as all get out.

earl87gta · 11-01-2007, 02:03 AM

I would love to have one of those and turn it in to a cofee talbel or maybe a bar.

Mickey_D · 11-01-2007, 04:43 AM

I would love to have one of those to put into a truck that could handle it for hauling firewood.

12 chords at a time!!!

earl87gta · 11-01-2007, 04:52 AM

that would be one long truck

Mickey_D · 11-01-2007, 05:27 AM

Nah, just mount the radiator on the front of the support (more towards the grill) and chop and channel the firewall to make a bigger bell housing hump. I mean, they put inline sixes in these trucks, all that engine is is two I-6's sharing a crank.

Ok, maybe it's a little bit longer, but not by much, is it?

earl87gta · 11-01-2007, 05:33 AM

I would think its at least 4ft.

87 STEPPER · 11-01-2007, 07:14 AM

Here ya go TI25
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Mickey_D · 11-01-2007, 08:59 AM

Quote:

Originally Posted by earl87gta

I would think its at least 4ft.

Hrm, got me thinking here. It's a little more than 4 ft from the radiator support to the firewall on my truck.......

Nah, my old 1/2 ton would never handle it.

cayoterun · 11-01-2007, 09:15 PM

Length: 5' from tip of water pump to edge of flywheel housing.

Check www.6066gmcguy.org in the pic. gallery. I think its a '63 cab-over. One nice truck w/23,000 mi on it. Belonged to the Wisconsin Forest Service and was only used to pull a water supply tanker to fire trucks since new. Owner did a great job restoring it.
When he shows it, he or his wife take turns going to eat as someone is asking questions about the motor all day long. Some really sincere, but amusing.
Cayoterun

mikecaddy500 · 12-21-2017, 06:49 PM

Check out thunder v12. They build

high performance engines

cayoterun · 12-22-2017, 11:47 PM

Quote:

Originally Posted by NONHOG

Please tell me someone here has one

Check "cayoterun" see his posts , he has lots of pics ! GMC V-12 powered '91 Chev crewcab ( 1 2 3 4)[/QUOTE]

The pic is the end product of my '46 Chev pu. It's all sitting on an '84 GMC 3/4 ton running gear. It has a 700R4 auto tranny mated to it. I grafted all the ps, pb over on it, from the '84. To repeat from the build thread, that engine sit on an irrigation well for 22 years with only one .30 over overhaul pumping 2200 gallons per minute.

I cared for it for about a year working for the farmer, and it won my respect for being a tough old critter. I always like to watch the fire out all 4 exhaust pipes, and manifolds glowing cherry red when I checked just before bed time at night.

It's started and driven a for a mile or two now and then just to stay lubed, but living a pampered life snuggled down in the corner of my farm shop. I have it on propane, but it burned natural gas when on the well.

**special-K** · 12-23-2017, 07:42 AM

This b-model belonged to a great local GMC enthusiast, Fred Craig,who passed away some years back. This was in '07 when I took the pictures. I wonder where it went to when sold. It's out there somewhere.

10-31-2007, 05:37 PM	#2
WorkinLonghorn Senior Member Join Date: Dec 2006 Location: Studio City, Calif. Posts: 2,855	Re: The mother of all engines, the GMC Twin-Six V12 I have two.....on my spec sheet that's been kicking around for 20 years. Pretty cool. I always wondered what they looked like. __________________ '69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, 2nd owner, Work-Truck supreme. Best $300 I ever spent.

10-31-2007, 05:50 PM	#3
NONHOG Registered User Join Date: Feb 2007 Location: Marana, Arizona Posts: 3,416	Re: The mother of all engines, the GMC Twin-Six V12 Please tell me someone here has one[/QUOTE] Check "cayoterun" see his posts , he has lots of pics ! GMC V-12 powered '91 Chev crewcab ( 1 2 3 4) __________________ "I feel the need for speed!"... as soon as I am done with my nap. Last edited by NONHOG; 10-31-2007 at 05:56 PM. Reason: added link ? sp

10-31-2007, 05:52 PM	#4
texanidiot25 Eat My Rust Join Date: Jan 2007 Location: Cypress, Texas Posts: 3,362	Re: The mother of all engines, the GMC Twin-Six V12 Sure will. I really want to hear this thing too... but I cant find any video.

10-31-2007, 07:20 PM	#5
cayoterun Junior Member Join Date: Dec 2006 Location: Guymon, Oklahoma Posts: 2,040	Re: The mother of all engines, the GMC Twin-Six V12 Hello-- Hope to submit a video, with sound, before tooo long,but as posted, project posponed due to family illness. Last pic posted is where we are. It shouldn't be too far from running when we can get back to work. Join us with this project, and give your ideas. Thanks Cayoterun Oh, save a post. What's the wheelbase on a 1ton Xcab- late 80s, early 90s??? __________________ Cayoterun Okla. Panhandle I think I'll do it myself and pay the extra $500.

10-31-2007, 08:38 PM	#6
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: The mother of all engines, the GMC Twin-Six V12 someone had a photo of one in front of a junk yard.

10-31-2007, 08:53 PM	#7
724x4a/cchevy Self-proclaimed LED man Join Date: Nov 2003 Location: Harrisburg, Missouri Posts: 1,021	Re: The mother of all engines, the GMC Twin-Six V12 Here ya go longhorn. Pretty sure this is the one you are talking about. __________________ My LED Website My Photobucket Album of LED's Ask me about hand-made custom L.E.D brake and reverse lights. <- LINK I also do LED: -Third Brake/Cargo -Brake (truck and burb) -Reverse (truck and burb) -67-68 Front Turn Signals -69-70 Front Turn Signals -71-72 Front Turn Signals -GMC Front Turn Signals I can also do custom lights for other vehicles....i did a set for a AMC Gremlin once Norwood Survivor

10-31-2007, 09:23 PM	#8
67_C-30 I have a radical idea! Join Date: Jan 2005 Location: Sweet Home Alabama! Posts: 6,513	Re: The mother of all engines, the GMC Twin-Six V12 I have a coiuple of 305 V6's and a 351 Magnum V6, but no V12's. I don't what the hell I'd do with it, but I'd love to have one!! Here's some more pics, ads and drawings. A bad crank out of one of these would make a killer mailbox post wouldn't it?? Attached Images __________________ '67 C-30 Dually Pickup 6.2 Turbo Diesel, NP435 ‘72 C-10 SWB , 350 4bbl, TH350 '69 C-10 SWB , 250 L6, 3 OTT '69 GMC C3500, dump truck, 351 V6, NP435 '84 M1009 CUCV Military Blazer 67 C-30 Turbodiesel build thread http://67-72chevytrucks.com/vboard/s...d.php?t=254096 My trucks http://s226.photobucket.com/albums/d...ediafilter=all Member of the 1-Ton Club!

10-31-2007, 09:27 PM	#9
67_C-30 I have a radical idea! Join Date: Jan 2005 Location: Sweet Home Alabama! Posts: 6,513	Re: The mother of all engines, the GMC Twin-Six V12 Oh, I almost! The coolest GMC V-12 powered vehicle on Earth!!! The B-702! Attached Images __________________ '67 C-30 Dually Pickup 6.2 Turbo Diesel, NP435 ‘72 C-10 SWB , 350 4bbl, TH350 '69 C-10 SWB , 250 L6, 3 OTT '69 GMC C3500, dump truck, 351 V6, NP435 '84 M1009 CUCV Military Blazer 67 C-30 Turbodiesel build thread http://67-72chevytrucks.com/vboard/s...d.php?t=254096 My trucks http://s226.photobucket.com/albums/d...ediafilter=all Member of the 1-Ton Club! Last edited by 67_C-30; 10-31-2007 at 09:30 PM.

10-31-2007, 09:29 PM	#10
67_C-30 I have a radical idea! Join Date: Jan 2005 Location: Sweet Home Alabama! Posts: 6,513	Re: The mother of all engines, the GMC Twin-Six V12 Then there's Frankenstein!! Attached Images __________________ '67 C-30 Dually Pickup 6.2 Turbo Diesel, NP435 ‘72 C-10 SWB , 350 4bbl, TH350 '69 C-10 SWB , 250 L6, 3 OTT '69 GMC C3500, dump truck, 351 V6, NP435 '84 M1009 CUCV Military Blazer 67 C-30 Turbodiesel build thread http://67-72chevytrucks.com/vboard/s...d.php?t=254096 My trucks http://s226.photobucket.com/albums/d...ediafilter=all Member of the 1-Ton Club!

10-31-2007, 09:54 PM	#11
Stepside65 Still Truckless! Join Date: Jul 2007 Location: Valrico, Florida Posts: 3,166	Re: The mother of all engines, the GMC Twin-Six V12 Gotta love the giant motor. __________________ ~James Truckless 2009 Hyundai Sonata<~~Wife's sedanomatic 1997 Nissan Pickup Father-in-law's tonka toy I am forced to drive Founder of The 60-66 Club Tutor Et Ultor

10-31-2007, 10:28 PM	#13
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,852	Re: The mother of all engines, the GMC Twin-Six V12 I was gonna say the 702 would be awesome in a rat rod.Talk about funky obscure. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

10-31-2007, 11:03 PM	#14
Hoods69BadBowTie Chevys Kick A$$ Join Date: Jan 2005 Location: Zootown, MT Posts: 12,699	Re: The mother of all engines, the GMC Twin-Six V12 Wow thats pretty kool. Not very burly motor but defiantly unique as all get out. __________________ HOODS is what I answer too -'79, '77, '88 Pickup Sold, '85 Camaro, '83 T/A, '81,'83,'90 K5 Blazer All Sold -'79 3/4 ton "Big Yellow Bananna" Lifted 4spd. 39.5 TSL Swampers, The money Pit -'86 K5 Blazer Silverado 6.2 4" lift 35"s -'95 Ext. Cab Shorty 4" Tuff Country rolling 35" M/T's -'83 Monte Carlo T-Tops. 126,500 Original Miles -LATER I would rather push a Chevy then drive a ford!!

11-01-2007, 02:03 AM	#15
earl87gta Senior Member Join Date: Dec 2003 Location: Kingsport TN Posts: 4,641	Re: The mother of all engines, the GMC Twin-Six V12 I would love to have one of those and turn it in to a cofee talbel or maybe a bar. __________________ Earl 68 2500 4x4 GMC Burb

11-01-2007, 04:43 AM	#16
Mickey_D Dirteh Kitteh Join Date: Nov 2006 Location: Mormon country Posts: 2,484	Re: The mother of all engines, the GMC Twin-Six V12 I would love to have one of those to put into a truck that could handle it for hauling firewood. 12 chords at a time!!! __________________ Darrin 1955 Willys CJ-5 all original and the oldest CJ-5 on the road. 2001 Dodge Neon (wife's car) 1995 Jeep Grand Cherokee Limited Edition SOLD 1981 K15 Custom Deluxe 4X4, rusty but trusty wood hauler. SOLD 1993 S-10 4X4 Tahoe SOLD Sign up with the Contact List RIP ESLL

11-01-2007, 04:52 AM	#17
earl87gta Senior Member Join Date: Dec 2003 Location: Kingsport TN Posts: 4,641	Re: The mother of all engines, the GMC Twin-Six V12 that would be one long truck __________________ Earl 68 2500 4x4 GMC Burb



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11-01-2007, 05:27 AM	#18
Mickey_D Dirteh Kitteh Join Date: Nov 2006 Location: Mormon country Posts: 2,484	Re: The mother of all engines, the GMC Twin-Six V12 Nah, just mount the radiator on the front of the support (more towards the grill) and chop and channel the firewall to make a bigger bell housing hump. I mean, they put inline sixes in these trucks, all that engine is is two I-6's sharing a crank. Ok, maybe it's a little bit longer, but not by much, is it? __________________ Darrin 1955 Willys CJ-5 all original and the oldest CJ-5 on the road. 2001 Dodge Neon (wife's car) 1995 Jeep Grand Cherokee Limited Edition SOLD 1981 K15 Custom Deluxe 4X4, rusty but trusty wood hauler. SOLD 1993 S-10 4X4 Tahoe SOLD Sign up with the Contact List RIP ESLL

11-01-2007, 05:33 AM	#19
earl87gta Senior Member Join Date: Dec 2003 Location: Kingsport TN Posts: 4,641	Re: The mother of all engines, the GMC Twin-Six V12 I would think its at least 4ft. __________________ Earl 68 2500 4x4 GMC Burb

11-01-2007, 07:14 AM	#20
87 STEPPER STILL PLAYS WITH TRUX Join Date: Nov 2002 Location: Melbourne, Fla. Posts: 2,764	Re: The mother of all engines, the GMC Twin-Six V12 Here ya go TI25 __________________ ~~Bruce~~ MY 87 STEPPER MY 99 2D/WD TAHOE

11-01-2007, 09:15 PM	#22
cayoterun Junior Member Join Date: Dec 2006 Location: Guymon, Oklahoma Posts: 2,040	Re: The mother of all engines, the GMC Twin-Six V12 Length: 5' from tip of water pump to edge of flywheel housing. Check www.6066gmcguy.org in the pic. gallery. I think its a '63 cab-over. One nice truck w/23,000 mi on it. Belonged to the Wisconsin Forest Service and was only used to pull a water supply tanker to fire trucks since new. Owner did a great job restoring it. When he shows it, he or his wife take turns going to eat as someone is asking questions about the motor all day long. Some really sincere, but amusing. Cayoterun __________________ Cayoterun Okla. Panhandle I think I'll do it myself and pay the extra $500. Last edited by cayoterun; 11-01-2007 at 09:25 PM.

12-21-2017, 06:49 PM	#23
mikecaddy500 Registered User Join Date: Jan 2015 Location: howard city mi Posts: 83	Re: The mother of all engines, the GMC Twin-Six V12 Check out thunder v12. They build high performance engines

12-23-2017, 07:42 AM	#25
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,852	Re: The mother of all engines, the GMC Twin-Six V12 This b-model belonged to a great local GMC enthusiast, Fred Craig,who passed away some years back. This was in '07 when I took the pictures. I wonder where it went to when sold. It's out there somewhere. Attached Images __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

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