GMC V-12

[ztwntyn8]

realy effin responsive breath

[jrkepler]

This isn't really that impressive of an engine. It was huge, heavy with really quite modest horsepower for its size. It was rated at 250 HP despite its massive displacement. This really was about the last effort, the diesels were just so much better for trucks that standard petrol engines just couldn't compete, really a treat to see one of these rare pieces in working order.

[LocomotiveBreth]

@jrkepler You are slightly off on your HP numbers. The 7.5 to 1 compression truck engines were rated at 275 HP and 630 ft. lbs. of torque from 1600 to 1900. This engine has the 9.0 to 1 natural gas pistons, and bigger carburetors, it's probably around 300 HP and 650+ ft. lbs. of torque. A modern naturally aspirated diesel of the same displacement would be similar. Add boost to either engine and the numbers go way up. The rising price of gasoline and poor economy is what killed the big gas engs.

[scott93257]

@LocomotiveBreth

Your engine is a thing of beauty. It's too bad what the economy has done to these things...

[rewind48]

imagine..... dohc, efi, electronic ignition, and dual stage quad turbochargers feeding into one intake manifold.......



[28yogy4todd]

I've got the little brother engine in my 59 gmc, the 305 ci V-6

[TheVooDooReverend]

This is called the GMC Twin-Six



[cedartowndawg]

Is that a legit v12 or just two v6s ran cam to cam?

[LocomotiveBreth]

@cedartowndawg Its a real V12, one piece block, crank, cam, just uses heads, manifolds, valve covers off the V6 version.

[cedartowndawg]

@LocomotiveBreth Ahh, alright. Makes sense in terms of cost and availability.

[slimjim119]

how many hp does it has

[kolbpilot]

Cool stuff, never knew this engine existed. Penny pinching GM mating 2 v6s' together to get a cheap v12. Not saying it is not a good idea.

[sandman19681012]

Great old engine...output?

[LocomotiveBreth]

It is 702 cubic inches

[bloodhoun234]

@LocomotiveBreth are you rich or something? i've looked through your videos and holy fuck you have alot of cars, post some videos how far along you got on the mustang with the tank engine

[LocomotiveBreth]

@bloodhoun234 No, I am far from being rich. If I was the Mustang and a few others would be finished by now.

[1994fergo]

out of interest how many cubic inch is it?

[sandman19681012]

@1994fergo 702 I believe. GMC made this engine by mating two 351 cubic inch V6 engines together.

[LocomotiveBreth]

@sandman19681012 It is a one piece block, crank, and camshaft, most other pieces interchange with a 351 V6

[LynolsOffice]

Wow, that thing is so big! It sounds great!

[albiz94]

ferrari's v12 long lifelong life to the ferrari v12

[DRNEGOLICIS]

ferraris v12 is weak compaired to a chevy v12

[albiz94]

can a chevy v12 make more than 120 cv/liter?

[DRNEGOLICIS]

do what?

[albiz94]

more than 120hp/liter

(i used cv couse here in itali we use cv, that are near the same of hp)

[DRNEGOLICIS]

what the heck does CV stand for? liter? hp/liter? this engine is 702CID 275HP @2000 RPM and 750FTlbs of torq the high power version with bigger carbs and cam and stuff i belive is around 880FT LBS of torq at 2200RPMs and maybe 300HP horse power dont mean any thing though its all about torq

[albiz94]

ot mani liters? 7.5? a 6.0 ferrari v12 can make 800 hp and 500 lbs

[DRNEGOLICIS]

i think its 11.5 liters 702cubic inches

[albiz94]

so this

hp/liter= 300/11.5= 26

lb/liter= 880/11.5=76

ferrari v12

hp/liter= 800/6= 133

lb/liter= 500/6= 83

and a ferrari v12 can rev up to 9-10 rpm

[albiz94]

9-10 k of course

[madzyzome]

Actually it's all about horsepower. Horsepower is 550 ft·lbf/s so that's torque over time. Torque can be multiplied by dividing time. When I set up a Ford 8.8 rear end I use 400ft/lbs torque to set the pinion bearing preload and I do that with my bare hands. A transmission multiplies torque but not horsepower. The thing about large slow low power engines like this it the duty cycle. That is 275hp continuously day in and day out whereas a Ferrari V12 is 800hp for a few 10's of seconds at a time.

[DRNEGOLICIS]

heres the thing about the chevy v12 i seen a guy put one in a suburban the engine weighs about 1700lbs the guy had dual transmissions in the truck he would dtrag race it the engines highest RPM is 2,500RPM when the ferrari probbably turns like 10,000RPM the power ban on the chevy v12 is between 500RPM and 2500RPM the guy would do 9s with the suburban depending on how fast he would shift it that day the trucks top speed in a quarter mile was 200MPH he achived this with useing an over drive trans

[DRNEGOLICIS]

mission behind his main transmission

[robby844]

the trans would never get into OD.

[DRNEGOLICIS]

@robby844 lol yeah it would already be going to fast

[robby844]

um no it would never get out of third.

[505197]

@DRNEGOLICIS In your dreams maybe. Figure out what knda gear it takes to hit 200 with 2500 rpm , probably a 1 to 3 or 4, they don't make enough overdrive to make that sob go 200. Maybe if you towed it with a AA/Fueler but you better have a hell of a hitch. 

[robby844]

dude are you high? the ferrari is designed to run at 12 grand all day everyday for 7 days and 7 nights.

[Alisterwolf66]

What Chevy V12? The engine in this vid is a GMC "Twin-Six" - designed and manufactured by GMC, not. Chevy, between 1960 and early '66 (replaced by the 637 V8 in '66).

[DRNEGOLICIS]

@Alisterwolf66 Chevy and GMC are the same even when i work on a oldsmobile we call it a chevy its all the same

[remo1366]

@DRNEGOLICIS except for the fact that chevy NEVER offered this or any of it's v-6 cousins in any c model.And, I'd take my low revving rocket 350 over a small block bow tie any day,the differences may be small but the same they ain't...

[mbsnyderc]

what where these engines for?looks like two of the big block v6's in my 64 GMC pickup mated together.

[BeephLypz]

they used them in Fire Trucks and stuff

[mbsnyderc]

thanks that makes sense.

[LocomotiveBreth]

There is a lot of GMC V6 and V12 info. on the  GMC 6066 website.

[paulmerz]

Needs a half dozen Weber DCOE..would sound much better!

And, of course, look better.

[wickedblackcamaro]

what the hell is this, two 4.3's mated at the crank? Did GMC actually make an engine like this, how much power?

[2fit661cars]

nope, it's two 5.7 liter 351s. although, actually it was built as a v12 because it had one block, crankshaft, ect..

[DRNEGOLICIS]

its one crank one block one cam 4 351 heads 12 351 pistons and two 351 intakes it puts out around 200hp but has more torque than any ones brain can handle they get 1mpg in a truck 3mpg at best

[LocomotiveBreth]

Actually the truck engine is rated at 275 HP, but this one has the high compression natural gas pistons so it's probably around 300 HP. The bigger carburetors help some too.

[DRNEGOLICIS]

one of them produces i think around 750 FT lbs of torq and the other i belive 600 ft lbs its been a while i forgot the exact numbers

[DRNEGOLICIS]

the high power version is 880FT lbs of tork i think?

[DRNEGOLICIS]

3MPG is pretty good i get 4mpg in my truck and im running a 350

[madzyzome]

Is your truck a tank? There is something wrong with your truck if you are getting 4mpg from a 350. You should get a tuneup ASAP.

[DRNEGOLICIS]

nope its all fine to go 70MPH my engine revs 3800RPMs im running a SM465 transmission with 4.52 rear gears i get 4MPG with my heavy foot opening the secondairys if i drive like a granny and keep them closed i get 15 - 17MPG and the truck is all stock cept i upgraded to a holly 650 for better gasmilage with the quadra jet i got 4-7MPG regardless of how hard i drove it or how easy i was on it

[DRNEGOLICIS]

@DRNEGOLICIS 5.52 rear gears

[DRNEGOLICIS]

@madzyzome it is tuned up it ended up haveing a bad leak on the accelorator pump now i get 8city 17highway

[DRNEGOLICIS]

@madzyzome i just got a 1997 z71 it gets 5mpg untill i took off the cats and blocked the EGR now i get 7 it neds new O2 sensors

[JoPissvengance]

are those 440 six packs?

[ilovehappyemos]

it says GM right in the name. the 440 is a chrysler motor.

[scott93257]

@ilovehappyemos

yeah and GMC is clearly stamped on the valve covers

[saludahead]

Great old motor! I've worked on a few of them in my day!

Remember to blow the area around the spark plugs out with air real, REAL good before you pull a plug out! it's a real bitch to have to pull a head because a piece of unknown crud dropped into the cylinder!

Run Shell Rotella with a two quarts of Lucas in it. The tolerances in those old Jimmys are pretty slack even when they're new!

[LocomotiveBreth]

Yeah I know what you mean about cleaning around the plugs before pulling them. They are very easy to change but no telling how many engines were damaged from people not doing that.

I run Mobil Delvac 1300, 15-40 in just about everything except our new pickup. I usually add a quart of STP as well. I have never tried the Lucas product, I may have to give it a try.

[goinghomealive]

lucas is really messy,i put it in my car to quiet the lifters from tapping and it didnt help

[19mg94]

@LocomotiveBreth lucas is the stuff to use

[kennethrobinson123]

@saludahead Lucasis a joke. The v12 on the back of the truck you see here on youtube was mine. I live in KY. where it cold but not like up north. Used shell Rotella-t 30w in cold temp. 40w in hot temp. Never used 10w30 or 15w40. used straight weight only. V12 used solid lifters. Rotella is made for these lifters

[kennethrobinson123]

@kennethrobinson123 Some of the first engine used solid lifters I had them.

[acuarofilio]

its beautiful

[Hotrodx199]

I want this in my 68 jimmy pickup! But i'm probably gonna have to either make a custom dog house in the cab or extend the hood quite a bit LOL

[goinghomealive]

i know where a 67-72 model suburban/jimmy is at.1500 bucks and it does'nt have alot of cancer

[punhoss]

I bet that block and crank are hard to come by....? How many of these engines did GMC produce? Sounds great by the way! ; )

[duanedragon2]

I would like to apologize ahead of time for my ignorance about these engines. Is that a gas or diesel engine? I can't tell if the wires/tubes loomed together nearest the lifter galley are hardlines from the injector pump to individual injectors or if they are part of the primary wiring; I don't see a distributor either. This is going to keep me up nights trying to figure out what I just saw.

[LocomotiveBreth]

It is a gas engine. The plugs go in from the top between the intake runners, they are very easy to change. The distributor is in the back and uses two six cylinder distributor caps.

[Alisterwolf66]

LocomotiveBreth already answered your question - I'm just adding a bit more info for you.

These GMC-only engines (optional in some big Chevy applications) came on scene in 1960 and ended production in about 1974. The vast majority were the V6s. All were 60° V-configuration. They were offered in displacements of 305ci, 351, 379, 402, 432, 478, 637 (60° V8 - used a balance shaft), and the 702ci "Twin Six" you see here. To be continued...

[Alisterwolf66]

Continued...

In addition to the extensive range of displacements available, the 478 V6 and 637 V8 were offered as diesel versions, named the Toro-Flow diesels.

The Twin Six was essentially two 351 V6s, however they used a single block, crank, and camshaft - not a bolt-together layout common to bigger Detroit diesels (like the 12V92). They did use four heads, two intakes, two carburetors, and an interesting bevel-drive twin distributor.

Google '6066 GMC' for GMC Guy's page and more info.

[LocomotiveBreth]

Because it would be a waste of money and time to dyno a basically stock engine. In it's current form it will make around 300 HP at 2800 rpm and 650 ft. lbs. from 1200 to 1800 rpms. Just like any other engine, it can be modified to produce more power if necessary.

[originalbrownirish]

stick it on a dyno

[LocomotiveBreth]

Why?

[originalbrownirish]

lol why not find out how power it's making it would b very interesting, how much hp would u get with 702ci

[wilsonces]

Mmmm, naughty hand ... :-p

[30GB]

GMC for ya

[LocomotiveBreth]

It has a one piece block, crank, and camshaft, but uses 4 heads, 4 exh. manifolds, and 2 intakes. Same bore and stroke as the GMC 351 V6.

[preacherboy244]

Is that two v6s glued together or one engine?

[DionysiosA76]

actually welded, but yes...lol

[haystack155]

Looking good, sounding better!!! Carb adapters are good. Looking forward seeing it in the coe.

Cayoterun

[Trendyrapslut]

That thing is huuuge. You got room for it, lol.

[LocomotiveBreth]

"That thing is huuuge."

I bet you say that to all the guys with big motors.

[Trendyrapslut]

No...Just havent seen many car/truck engines that long. What are you trying to say?