any of you big truck guys got a GMC with a 12 in it? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

greywuuf · 01-09-2012, 06:54 PM

One of my old repair manuals listed specs for the v12 GMC truck motors. I have heard rumors that they are basicly twinned V6's. I would love to find out more, and or see some pictures.

Thanks.
Dan

Posted via Mobile Device

Steve-W · 01-09-2012, 06:59 PM

12 gauge? 12 inch, 12 lepricons?
1 have 2x an empty sixpack..that makes 12

greywuuf · 01-09-2012, 07:02 PM

Cylinders.....with something in the neighborhood of 6-700 inches if displacement.
Posted via Mobile Device

ls1nova71 · 01-09-2012, 07:08 PM

About 20 years ago or so there was a 7-up truck in a salvage yard near me that had one in it, I never got to look at the engine, but it did have really cool V12 emblems on the hood.

C10 - C90 Bill · 01-09-2012, 08:15 PM

Dan,

The V-12 GMC is a 702. It is kind of like you mentioned, it is basically 2 351 V-6's together. There are actually some on YouTube. I will also try to post some links.

Bill

C10 - C90 Bill · 01-09-2012, 08:19 PM

Here is a good example:

GMC V-12 - YouTube

C10 - C90 Bill · 01-09-2012, 08:24 PM

Here is some good info on it from Jolly's site:

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

There is also some other links on there for additional info.

Bill

Steve-W · 01-09-2012, 08:31 PM

that looks a lot like 2 six cylinders put together..GMC was years ahead on VW with their W12

greywuuf · 01-09-2012, 09:30 PM

So who is driving one? What were they like? Seems like a real neat restoration piece.
I thought I rememered 702 , but not being a v6 guy I only new for certain the 305 existed (and that would only be a 610).
Posted via Mobile Device

Hutch · 01-09-2012, 10:02 PM

greywuuf,
Member cayoterun has one
Here is the Build thread http://67-72chevytrucks.com/vboard/s...d.php?t=254111

**Bob B.** · 01-10-2012, 04:58 AM

I have seen a few. They were somewhat popular in fire trucks. GMC made them from 1960-1965, when they were replaced by a 637 V-8. The 637 was basically the 478 V-6 with 2 more cylinders. It came in both gasoline and Toro-Flow diesel versions.

**special-K** · 01-10-2012, 06:13 AM

I was gonna say what Bob already did. These year trucks didn't get them. They were a thing of the past already. They were two 351s. When I saw this thread I thought you might be talking about the Detroit 12. Now that's a power plant!!!

C10 - C90 Bill · 01-10-2012, 09:05 AM

Quote:

Originally Posted by greywuuf

So who is driving one? What were they like?
I thought I rememered 702 , but not being a v6 guy I only new for certain the 305 existed.
Posted via Mobile Device

Dan,

In a V-6 they made the 305, 351, 401 and the 478. In the V-8 version, as Bob has mentioned, it was the 637. They also made two newer versions of the V-6 in the '70's but they weren't that popular (379 and 432, I believe).

I never drove a 702, but have driven a 478 and a 637.

Bill

C10 - C90 Bill · 01-10-2012, 09:51 AM

Here is an example of the V-12 Detroit Diesel (12V-71) that Tim was talking about:

12v71 - YouTube

Believe it or not, it is qusetionable that any were ever put into a GMC by the factory, even though GMC made an Extended Hood version of the 9500. Most say no, but a few have stated yes. If there are any, they are very rare.

Bill

C10 - C90 Bill · 01-10-2012, 10:07 AM

Quote:

Originally Posted by Hutch

greywuuf,
Member cayoterun has one
Here is the Build thread http://67-72chevytrucks.com/vboard/s...d.php?t=254111

Hutch,

That truck is cool.

**special-K** · 01-10-2012, 10:21 AM

Here's a couple on the wild side:

International Detroit Diesel 12v71TT sled pull...

1960 Peterbilt Hotrod Truck called Piss'd Off...

A little smaller plant,but I just have to share cuz I LOVE IT!

Detroit Diesel Powered Chev - YouTube

PanelDeland · 01-10-2012, 10:59 AM

A lot of the V12 engines were used by farmers.Not to run their trucks but as power sources for their irrigation pumps.I met a guy who had a bussiness tuning and maintaining them.IIRC they were torque monsters but had limited ability to turn much in the way of RPM's.

coops714x4 · 01-10-2012, 11:24 AM

In the early 80's I worked for a company that had a GMC with the V 12, it had a 5 and 4 transmission, nobody could drive it but me and I hated that thing. the truck looked like the big yellow wrecker in the wrecker thread, it had straight stacks (no mufflers) it was UNGODLY loud. it was FAST tho, it would peg the speedo in 5th and 2nd @ 1800 RPM, I don't know if it was turned up but the engine would turn 2600 RPM. But I have no idea if that is the way it came from GM or not. Coop

72freak · 01-10-2012, 12:14 PM

Here is the coolest use of one I have seen in a long while. If i ever put my hands on one I have a project in mind for it. There was one here locally for sale a few years ago but he wanted way too much money for it.

**special-K** · 01-10-2012, 02:17 PM

It's nice to see that "thing" on the road and gettin' around. Here it is back in '10:

**Bob B.** · 01-10-2012, 04:12 PM

Quote:

Originally Posted by C10 - C90 Bill

Here is an example of the V-12 Detroit Diesel (12V-71) that Tim was talking about:

12v71 - YouTube

Believe it or not, it is qusetionable that any were ever put into a GMC by the factory, even though GMC made an Extended Hood version of the 9500. Most say no, but a few have stated yes. If there are any, they are very rare.

Bill

There has been a number of discussions over on the ATHS borads about what trucks came with the Detroit 12V-71's. Although none of the GMC 9500 long-nose conventionals were built with the 12V, a number of Astro 95 and Chevy Titan 90 cabovers were built with 12V's.

C10 - C90 Bill · 01-10-2012, 05:12 PM

Bob,

The ATHS is the site where I have actually learned that from. But there was one or two members on there that stated they had brand new, or fairly new 9500 Extended Hoods with 12V-71's. It sure was an interesting thread that went deep into details on both sides. That is why I stated "questionable" above, as most dis-agreed or just did not see it possible. It wasn't really that long ago and I'm sure it is still on file, in case you missed it.

Glad you mentioned the Cab-Overs. I had forgot about them.

Bill

**special-K** · 01-10-2012, 10:54 PM

http://forums.aths.org/InstantForum2010/Topic92709.aspx

C10 - C90 Bill · 01-11-2012, 02:13 AM

Tim, That's the one. Thanks for finding it.

Bob, I see that you were in on that thread as well.

By the way, Ashton Lewis was also there. His son, Ashton Lewis Jr, used to race in Nascar in the Busch Series.

Bill

**special-K** · 01-11-2012, 08:06 AM

You're welcome Bill. Ok,now I just have to show this beaut!

GMC 9500 Trailer-Bus Papa-Fila na VVR 2008 -...

01-09-2012, 06:54 PM	#1
greywuuf Registered User Join Date: Jul 2007 Location: Alaska Posts: 516	any of you big truck guys got a GMC with a 12 in it? One of my old repair manuals listed specs for the v12 GMC truck motors. I have heard rumors that they are basicly twinned V6's. I would love to find out more, and or see some pictures. Thanks. Dan Posted via Mobile Device

01-09-2012, 06:59 PM	#2
Steve-W Registered User Join Date: Aug 2010 Location: Hoofddorp, the Netherlands Posts: 582	Re: any of you big truck guys got a GMC with a 12 in it? 12 gauge? 12 inch, 12 lepricons? 1 have 2x an empty sixpack..that makes 12 __________________ Feedback is always welcome! projects: 1969 Chevy C10 1950 GMC 100 1958 Chevy C60 Viking ratrod

01-09-2012, 07:02 PM	#3
greywuuf Registered User Join Date: Jul 2007 Location: Alaska Posts: 516	Re: any of you big truck guys got a GMC with a 12 in it? Cylinders.....with something in the neighborhood of 6-700 inches if displacement. Posted via Mobile Device

01-09-2012, 07:08 PM	#4
ls1nova71 Registered User Join Date: Dec 2009 Location: Independence Mo Posts: 4,118	Re: any of you big truck guys got a GMC with a 12 in it? About 20 years ago or so there was a 7-up truck in a salvage yard near me that had one in it, I never got to look at the engine, but it did have really cool V12 emblems on the hood. __________________ My '72 short bed build. http://www.ls1tech.com/forums/conver...6-0-4l80e.html 5.3 swap into my RUSTY '71 C10 http://ls1tech.com/forums/conversion...71-c-10-a.html

01-09-2012, 08:15 PM	#5
C10 - C90 Bill Registered User Join Date: Nov 2001 Location: Moneta, VA USA Posts: 3,069	Re: any of you big truck guys got a GMC with a 12 in it? Dan, The V-12 GMC is a 702. It is kind of like you mentioned, it is basically 2 351 V-6's together. There are actually some on YouTube. I will also try to post some links. Bill __________________ '60-'72 Chev/GMC Fan GMC 9500 Fan Detroit Diesel Fan

01-09-2012, 08:24 PM	#7
C10 - C90 Bill Registered User Join Date: Nov 2001 Location: Moneta, VA USA Posts: 3,069	Re: any of you big truck guys got a GMC with a 12 in it? Here is some good info on it from Jolly's site: http://www.6066gmcguy.org/TwinSix.htm There is also some other links on there for additional info. Bill __________________ '60-'72 Chev/GMC Fan GMC 9500 Fan Detroit Diesel Fan

01-09-2012, 08:31 PM	#8
Steve-W Registered User Join Date: Aug 2010 Location: Hoofddorp, the Netherlands Posts: 582	Re: any of you big truck guys got a GMC with a 12 in it? that looks a lot like 2 six cylinders put together..GMC was years ahead on VW with their W12 __________________ Feedback is always welcome! projects: 1969 Chevy C10 1950 GMC 100 1958 Chevy C60 Viking ratrod

01-09-2012, 09:30 PM	#9
greywuuf Registered User Join Date: Jul 2007 Location: Alaska Posts: 516	Re: any of you big truck guys got a GMC with a 12 in it? So who is driving one? What were they like? Seems like a real neat restoration piece. I thought I rememered 702 , but not being a v6 guy I only new for certain the 305 existed (and that would only be a 610). Posted via Mobile Device

01-09-2012, 10:02 PM	#10
Hutch Registered User Join Date: Oct 2001 Location: Grapevine, Tx. Posts: 2,142	Re: any of you big truck guys got a GMC with a 12 in it? greywuuf, Member cayoterun has one Here is the Build thread http://67-72chevytrucks.com/vboard/s...d.php?t=254111 Attached Images __________________ John Hutchison Grapevine,Texas 68 1/2 t swb 68 Mustang 69 Jaguar 71 1/2 t swb 88 Supra CompTs6m 93 Escort GT 2005 Corolla XRS

01-10-2012, 04:58 AM	#11
Bob B. Senior Member Join Date: Aug 2005 Location: Los Angeles Posts: 1,314	Re: any of you big truck guys got a GMC with a 12 in it? I have seen a few. They were somewhat popular in fire trucks. GMC made them from 1960-1965, when they were replaced by a 637 V-8. The 637 was basically the 478 V-6 with 2 more cylinders. It came in both gasoline and Toro-Flow diesel versions. __________________ 1967 GMC CM-2500 Camper Cruiser, 351E V-6, NP 435 4 speed, Dana 60, and factory A/C. 2012 GMC K-3500 WT regular cab, 6.0L Vortec, 6L90.

01-10-2012, 06:13 AM	#12
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,862	Re: any of you big truck guys got a GMC with a 12 in it? I was gonna say what Bob already did. These year trucks didn't get them. They were a thing of the past already. They were two 351s. When I saw this thread I thought you might be talking about the Detroit 12. Now that's a power plant!!! __________________ "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 ~

01-10-2012, 10:59 AM	#17
PanelDeland I am a Referee of life. Join Date: Jun 2000 Location: Greensboro N.C. Posts: 13,993	Re: any of you big truck guys got a GMC with a 12 in it? A lot of the V12 engines were used by farmers.Not to run their trucks but as power sources for their irrigation pumps.I met a guy who had a bussiness tuning and maintaining them.IIRC they were torque monsters but had limited ability to turn much in the way of RPM's. __________________ The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion. You can't fix stupid,not even with duct tape. "My appearance is due to the fact that "GOD" does punish you for having too much fun!" Barrett-Jackson has perfected alchemy,they make rust into gold! "You can lead a horse to water but you can't saddle a duck" "Cleverly disguised as a 'Responsible Adult' "Sometimes your Knight in shining armor is just a retard in tinfoil"

01-10-2012, 11:24 AM	#18
coops714x4 Registered User Join Date: Mar 2011 Location: Cement Oklahoma Posts: 916	Re: any of you big truck guys got a GMC with a 12 in it? In the early 80's I worked for a company that had a GMC with the V 12, it had a 5 and 4 transmission, nobody could drive it but me and I hated that thing. the truck looked like the big yellow wrecker in the wrecker thread, it had straight stacks (no mufflers) it was UNGODLY loud. it was FAST tho, it would peg the speedo in 5th and 2nd @ 1800 RPM, I don't know if it was turned up but the engine would turn 2600 RPM. But I have no idea if that is the way it came from GM or not. Coop __________________ 1971 K20, Coop's beast (project) 1972 C30 wrecker, "Big Ernest" (SOLD) 1975 K5 Blazer (wife's toy) she got it in the divorce 2014 Street Glide Special 1983 K20 Big Block, auto (work horse)

01-10-2012, 12:14 PM	#19
72freak Rottenwood Garage Member Join Date: May 2005 Location: Marietta, Georgia Posts: 4,321	Re: any of you big truck guys got a GMC with a 12 in it? Here is the coolest use of one I have seen in a long while. If i ever put my hands on one I have a project in mind for it. There was one here locally for sale a few years ago but he wanted way too much money for it. Attached Images __________________ 2004 Chevrolet Suburban C1500 2001 Chevrolet 2500HD Crew 6.0 1999 Harley Davidson Electra Glide 1972 Chevrolet C-20 Custom Camper "Dump Truck" 1972 Chevrolet C-20 Suburban "Big Green" 1969 Chevrolet C-50 Wedge Hauler "Leonidis" 1966 C-10 2x4 short fleet 327 4 speed "Race Truck" 1952 Plymouth Cranbrook "Rican" (my grandfathers) 1931 Ford Model A Coupe "Black Beauty" 1930 Ford Model A truck "Club Cab" 4x4 Rottenwood Garage and Speed Shop.....where everything must be racy! *It's not just a hobby..It's a LIFESTYLE!!!* Thanks for nothing Barrett-Jackson You cant fix stupid or teach accountability! Time wasters, looky Lous and tire kickers are everywhere!

01-10-2012, 02:17 PM	#20
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,862	Re: any of you big truck guys got a GMC with a 12 in it? It's nice to see that "thing" on the road and gettin' around. Here it is back in '10: __________________ "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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01-10-2012, 05:12 PM	#22
C10 - C90 Bill Registered User Join Date: Nov 2001 Location: Moneta, VA USA Posts: 3,069	Re: any of you big truck guys got a GMC with a 12 in it? Bob, The ATHS is the site where I have actually learned that from. But there was one or two members on there that stated they had brand new, or fairly new 9500 Extended Hoods with 12V-71's. It sure was an interesting thread that went deep into details on both sides. That is why I stated "questionable" above, as most dis-agreed or just did not see it possible. It wasn't really that long ago and I'm sure it is still on file, in case you missed it. Glad you mentioned the Cab-Overs. I had forgot about them. Bill __________________ '60-'72 Chev/GMC Fan GMC 9500 Fan Detroit Diesel Fan Last edited by C10 - C90 Bill; 01-10-2012 at 05:18 PM.

01-10-2012, 10:54 PM	#23
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,862	Re: any of you big truck guys got a GMC with a 12 in it? http://forums.aths.org/InstantForum2010/Topic92709.aspx __________________ "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 ~

01-11-2012, 02:13 AM	#24
C10 - C90 Bill Registered User Join Date: Nov 2001 Location: Moneta, VA USA Posts: 3,069	Re: any of you big truck guys got a GMC with a 12 in it? Tim, That's the one. Thanks for finding it. Bob, I see that you were in on that thread as well. By the way, Ashton Lewis was also there. His son, Ashton Lewis Jr, used to race in Nascar in the Busch Series. Bill __________________ '60-'72 Chev/GMC Fan GMC 9500 Fan Detroit Diesel Fan

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