There are 2 sides to longevity. In the oldern days testing how much each engine part needs to take was quite limited. So parts were sometimes much much stronger than they needed to be. When computer simulations became a thing it was much easier to design the parts just about as strong as they needed to be. So cheaper materials like plastic could be used instead of steel as well as less material in general and an overall smarter design. So today with ever advancing simulations cars are made cheaper than ever and with the market being extremely competetive that means in comparison cars are more affordable than ever today. In return they break more easily.
I remember during my auto parts days, a customer rebuilding a 305 v6. We had to break out the old dusty catalogs, but were able to find him bearings and gaskets! He was as surprised as we were!
I had the old 305 V6 in my GMC. The parts stores guys always corrected me, no sir the 305 is a V8 from the 70s....Nope, it's a huge V6, think it used the same size pistons as a 454. I totally rebuilt it, 30 over pistons, cam reground to a modern profile, heads shaved .080 to bring compression from about 7.7 to 8.2, ported the manifold to fit a holly 500 2BBL, changed point to electronic ignition... Yes would have been cheaper to buy a 350 but boring.
If I recall correctly, valve rotators were a $50.00 option on that engine. A neighbor of mine bought a GMC pickup new in '65, or '66 when I was a kid, and that truck ran into the 2000s with never any engine troubles whatsoever.
@@davef.2329 I did a front crossemember swap also, one from a later model like a 78 will bolt right in. Easiest way to get disk brakes, like $125 for the whole X-member with suspension and brakes.
My complements to you for an amazing video. The GMC V6 is the single most under appreciated engine. Paired with the legendary SM420 transmission with granny first gear, its simply amazing. It's a true technological marvel. These engines were so well designed they burned virtually no oil. Take it from a person that owns one.
I agree entirely. My father worked as a plant manager for GM back in 80's and early 90's. Since then, through a couple of businesses, we've collectively owned fleets of gm v6's and small-block v8's and some diesels though we mostly go with Cummins for that. Regardless, the v8's get the job done and are workhorses - but the v6's are the unsung heroes. I don't think I've ever seen one straight up die before the rest of the truck became unusable, and we were never kind to them in the field. They fit the perfect role in a supervisor or manager SUV or a people mover: good power so you'll rarely get stuck, good MPG over the v8's, and you can still tow a decent amount with them in a pinch! Can't tell you the number of times we saved leaving a trailer on site to potentially get stolen just because we went with V6 administrative vehicles over vehicles that could never tow.
@@ReggieGeorge probably saw the engine in my 92 sierra wt come off the line… 340k miles and only kicked out because i didn’t realize i had a hole in my radiator until it was too late
We still have a handful of them in farm trucks at our farm where we never get rid of anything we just park it. have two of our trucks still running with v6s. our dad's 67 Jimmy Farm pick up still down there it runs too just got old need new front end parts.
2:11 "Longevity and serviceability were the two major factors during its development", later you say it was capable making like 500k miles with minor service. 500000 miles, its around 800000 kilometers. And to think: it was made in 1950 - 70 years ago... Man, this engine was a real state-of-the-art beast! I love your vids VR, full of engines' history and wonderful sounds. You're a real proper engine nutjob around here. Thanks!
Some of the very best gasoline engines the US ever made were industrial and/or workhorse heavy duty motors for medium and heavy duty trucks. Well known for quality and longevity, a large step up from most of the usual motors they made for light trucks and cars.
Back in those days, cars were built to be 100k mile disposables compared to today. Cars were also much cheaper to purchase back then, and the idea of planned obsolescence was working due to significant leaps in auto safety from the 40s to the 80s in the USA. So, seeing an engine be produced in a time where that was going down makes it extra special.
It's a 1500 lb engine that cranked out under 300 hp, and was run under 3000 rpm. It had a lake for a cooling system, and a west Texas refinery for a sump. It ran a low compression ratio, but had a forged crank, and 4 bolt mains. In short, it was a war elephant used as a plow horse. That's a recipe for longevity.
@@ludditeneaderthal thats the key of it all. there were quite a few other engines made at the time that had exceptional longevity because they were built with low compression ratios and low red-lines. parts just arent subjected to extremes.
@@ludditeneaderthal very similar idea to the Toyota 5vz-fe v6. It's so undertuned and overbuilt it lasts 500k with proper maintenance (some are known to make it to 800k). Similar story with the 2uz v8.
You should do a video on the Hall-Scott ohc inline six (up to 1091 cubic inches) engines, and the V12 version. These engines were designed in the 1920's and were in production until the 1970's. They were used in buses, fire trucks, dump trucks, boats, stationary pump engines, etc. Way ahead of their time, and quite impressive.
You are correct! I worked at the Canton Ohio plant that was building them in the 1960's . We actually have one still active in a riverboat here in Elkhart In.
Once again Visioracer, you surprise us again with something old and new to us. That is an amazing engine. Keep up the great work you do. God bless you brother
I really great video! I didn't know they made a 956 but thought it was possible. I have 2 of these v12s, ive owned 8. I have owned every example of this family, 305s, 351s, 379, 401, 432, and 478s standard and "magnum" (bigger ports and valves) V6 engines and a 637 v8. except for the DH637 and DH351 toro-flow Diesels. Most in multiples. We have ran them from 1965 until now. Repowering many things with them on the farm. Dad, an engineer, fell in love with them while working at a GMC dealership. GMC isn't a division of Chevrolet. Rather, they were all part of General Motors Corporation. Just like Detroit Diesel, Cleveland Diesel, EMD, Euclid, Allison, Frigidaire etc. Chevy was the cheapest brand and for that reason alone became the most popular. My 478 toroflo diesel regularly got 27mpg in a cabover with an 18ft bed loaded. The first thing to do is chuck the timing light in the corner. Pull in as much advance as possible and hog out the jets and power valves until they smoke at full load. Then you have a whole new monster that eats Diesels for breakfast, and uses far less fuel than before. They were nutted for EPA reasons and frequently blew head gaskets and rings from pathetic 4deg ATDC timing and super lean jets. Later ones have bigger fastners and dual valve springs. I have accidentally had a balanced, ported, dual spring 401M with an 850 4bbl on a custom intake to 6300 rpm. They are extremely OVERSQUARE, a 478 is 5.125" bore x 3.86 stroke. A 401 is 4.875 x 3.58 huge pistons short stroke, huge valves (2.25" intakes) and 306deg duration cams made big bottom end torque, so low an electronic tach thinks it died! Then pull to 5k rpm.! Modern "stroker" engines couldn't even be warrantied in this type of service. I had a 1959 305A with 500,000 + miles, pulled it after the truck rotted off of it and. Then it farmed for 40 years in a tractor. It polished the cast iron block beside each rod throw from the oil over the years to a mirror! You won't knock a hole in the block with a sledgehammer either! Most people who got a turbo diesel after these cursed the lack of starting torque, excessive shifting, hard starting, and waiting for boost. Diesel torque is a myth when you tune up a big gasser! Great job!
@Prowbar yes, he was. Sadly he passed from 2 brain tumors. I became disabled from a non cancerous one a year before. Sold the farm and moved. Major communication issues caused almost all of that to become scrap. Even what i kept out was accidentally scrapped. But I still have two 702s and a few Detroits. A friend has his massey 1100 with the 478 in it. And a 401m we modified. Got some 305 boat anchors. Toroflows gone too. Saaad! Allisons gone too. Thanks for remembering!
@@Cletrac305 very sorry to hear that, I wasn't aware of that. As far as GMC engines go, I'm currently building up a 478 (non magnum) to replace the tired 305 in my '65 1500. I'd be interested in hearing what modifications and tricks you and your dad performed on those engines. I have implemented a few myself already. If you want, send me a private message through the 6066gmc forum. My name on the forum is Prowbar as well.
Thanks so much for making this video. I've always loved the GMC gasoline engines and lusted after the v12. We've had a couple of the 305 V6 is on the farm. One thing that I've always thought is interesting about that engine design is that they are very large bore and short stroke. It's the exact opposite of what you would think you would build for a torque producer. But, it absolutely works. They are extremely turkey motors that will pull at a very low RPM.
Air cooled aircraft engines are the same way, huge pistons ,shorter stroke. Pops has a 65hp Continental in his 46 luscombe. 65hp @2300 and it's 170 cubes. Nobody ever gave a torque number , but on paper it's around 150. And it'll never turn over 2800-3000, that's screaming! They had a 75 and 85hp version ,the 85 had higher compression ,but to jump from a 65 to a 75 it's basically adding timing and revving it a little higher , I think the 75hp rating was at 2500rpms. 75s had piston squirters too,and that was added in on his 65,but he left it set at the 65hp spec.
@@thomaskarlstrom4815 not really. You don't want huge valves for low rpm high torque engines, big valves means low intake velocity and bad mixture in the combustion chamber.
I'm pretty sure RPM is governed primarily by airflow, pertaining to both the intake plenum diameter and length. It's quite similar to port tuning on a subwoofer: given the same diameter, the longer the plenum or port, the lower the RPM or turning. Peak torque resides at whatever RPM causes sound to resonate within the plenum, thereby inducing greater airflow through the intake valves. The sound wave literally slams into the port just as its opening at peak torque RPM. The short stroke was mainly to minimize piston speed and maximize the engine's longevity. A longer stroke would have just meant an even lower redline RPM and untenably long intake plenums.
Something to bear in mind is that when these engines were common fuel prices were relatively low and stable. Gasoline in Pittsburgh was 20 cents per gallon, diesel was 15 cents. The concept of turbocharging diesels wasn't thought of in the 1960s, during the development of the interstate highway system, and diesel trucks were pigs on the hilly two-lane U.S. highway system. A friend of mine's dad drove a 1959 gas cabover Ford until the Arab oil embargo, then he went to a GMC crackerbox.
I was always told relative to inflation and other prices, gas was cheapest in the late 90s when I started driving. It was common to see $1.20 a gallon in California where I was and under $1 elsewhere.
Another guy that doesn’t convert those fuel prices of long ago for inflation. It was never nearly as cheap as so many people try to say. Why do you think “economy”cars that were easier on gas. came about back in the ‘50s?
@@joemonstermaker4784 True, gas has always been relatively expensive. The only reason people drove gas guzling monsters was they had extra money because everything was cheaper than today and there were less things to spend money on. No games, phones, ect.
I predict this will flip again. With diesel significantly more expensive than gasoline, emissions regulations killing diesel engines, and advancements in gasoline engines that allow them to be more efficient. I think we'll see large gasoline engines make a come back.
I am one of the fortunate still working a big block V6....478 Magnum in a '68 GMC dump truck.. I have several spares and even a diesel version. The best damn gasoline truck engines ever made!
@@jlo13800it was probably as good as the V6's and the V12. They are quite rare as by the time it replaced the V12 (1966 model year) the switch to diesel was just beginning in the medium duty market. Fire trucks seemed to be where most of them ended up. I'd love to fine one.
@@turbo8454 the twin six is a very emotion engine and it will make insane HP Per CID 2 stroke if you are happy. This alloy nickel block was designed by craig iron head heyward which is CGI high nickel will weaken if you are sad! If you are Happy its tensile strength is 235K psi but if you are sad is less than 80Kpsi! the fracture toughness goes down when you are bummed out! So pet it gently!
@@turbo8454 i fucking hate this 4 joke 702 and you can take a plasma cutter to it like any 4 joke stroke!If it dont run oil injection and run in multiple positions i have no use for it. 850 rotax anyone turbo
My wonderful Dad was the owner of a small family run trucking company in Rhode Island, from the early 50’s, till the teamsters put us out of business in 1981. In the beginning Dad specified International R190 Black Diamond gas engines six wheeled trucks, to haul 20-24’ refer bodies to haul meat, from the Boston Markets into R.I. Under grandfathered rules. But when the trucks aged Dad was forced to save money in able to grow the fleet he chose GMC 7500, 8500 an 9500 six wheeler straight trucks with 20-24’ refer bodies. All powered with 351/5 speed in the 7500’s up to the 401/5 speed w two speed axle. All GMC V6 big blocks. He also had one 5500, with a 305 V6, plus one with a V6 diesel version we called “The Shaker”, because of how it would shake at top rpm. But the gas V6’s all ran for over 200k before their first rebuild!
I drove the V6 with the "granny gear" 4 speed for a gas company in the late 60s. It idled so slow, I was able to flick it into low gear without crunching, without using the clutch.
I’ve been watching your channel for years and cannot help but comment how impressive your channel has become. The clips used, the flow of the script, the production details, every aspect of your channel production has come so far. Your English, too, has made huge strides. Congrats on your growth! You deserve every view and new subscriber.
I assume 4mpg was working under load, for the 60s that isnt too bad. The Diesel 6 wheeler i drive at work is 5.6mpg. And its $6.07 a gal of Diesel. MPG has gotten better. But you would think it would be MUCH better then what it is. Weight takes power to move, and energy. Be it battery or fuel. The instant mpg on the volvo 18 wheeler i drove would go down to 1.5mpg on bigger hills with loaded truck and trailer.
I would assume not. From what I've heard of its contemporaries, like Ford's 8.8 liter V8 Super Duty from the 50'-80's, was that they could haul anything, but fuel economy was usually closer to 3 MPG when doing work. Consider, too, that the way they kept heavy duty motors in those days running cooler was to also lower compression. Heavy Duty versions of the same motor actually LOST compression (usually dropping from 8:1 to 7.5:1) and were more inefficient. Good motors from Ford and GM, but I don't thin they were very efficient. We could get 10 MPG out of a 292 V8 in a F600 from 1958, empty. Which is impressive. But still....
@@kingduckford i got a 366ci 6.0L V8 hybrid it gets 23mpg around town 32-34mpg on the highway the battery is bad too it's just a combo of the transmission that helps put the numbers out.... at 40mph it's barely at 1000rpm at 65mph it's at 1400rpm
If manufacturers would finally switched to opposed piston diesels that would probably be about 8-9mpg or more... they demoed a 270hp pickup that got 37mpg combined city / highway. which is frankly double what pickups usually get... and that was without a hybrid system burning gasoline and not diesel. Achates power look them up... at least the goverment saw the value and is funding cummins to build a tank engine based on this.
I ve seen the GMC v6 . And I know they can run at low rpm. At idle you cam almost count the ignition cycles. But they were reliable and strong. But never knew the v12 engine existed that was derived from the v6
Best line of gasoline truck engines ever designed. Coupled with an SM-420 transmission and a 5:14 rear end and it was unstoppable with a wonderful soundtrack!
I remember when the V-6 was everywhere. When I was a child I remember my uncle's old packer style garbage truck had one, and a logger across from where my father used to go fishing had one that was kind of loud. But I always have remembered the sound of them compared to V-8s or any Detroit Diesels.
We have a Seagrave fire truck in our town. It has a V-12 in it. I used to put a sound system and PA system on it every Christmas for the kids. Our firetruck is awesome.
One minor quibble: GMC and Chevrolet are both divisions of General Motors. GMC is not a division of Chevrolet as stated in the video. In the era of this engine, there was very little in common between the mechanical components between GMC and Chevy.
The village where I live had a 702 equipped pumper in the fire truck fleet and I had to replace the twin disck clutch on Christmas Day, alone, early 1980s, in the fire house. No room to maneouver due to the water tanks, a Christmas I shall never forget.
I worked at a truck company in the late '60s/early '70s that had a couple of GMC V6 pickups/work trucks. They also had a lowboy with a GMC V6 powered winch. I never knew about the V12 though. They also had a White Cabover with a 327 for a spotter truck in the yard. I only drove it twice, I think, and then it disappeared.
I had a 1966 3/4 ton GMC pick-up with the 305 V6 it was a torque monster. A family friend had a Ford 3/4 ton pick-up with the 390 V8 he needed to take some stuff out to the coast so we loaded both trucks up. We stopped at the truck scale I had about 500 pounds more on than he did... on the hills I could climb up his without shifting out of 4th gear. He was down shifting on most hills of any grade. I wish I still had the old girl.
Wow, thanks for this video. I had seen a 305 v6, but never knew about the v12. I had heard from the son of the owner of the v6 that with enough weight, the front wheels would come off the ground from the torque
Happen to have a bit of knowledge of, and experience with this " LITTLE ENGINE " ! While it was obviously a conjoined twin-six design, it was an amazingly smooth running engine ! When in proper tune, it was nearly impossible to hear it running ! The " Blastolene Brothers " out of where else but California, built two absolutely gorgeous albe-they freaky custom design projects, they were then, and continue to be to this day, absolute torque monsters bringing the words " Made in the USA " some hardcore pride ! 🇺🇲
You have persevered in your field and today this reveal of the V12 GMC surpasses expectations. My compliments for the research and presentation you have put together. Your work is becoming very engaging finally. Your English speaking has improved vastly over time also ! Bravo Mr.
I grew up with a 1961 GMC 4000 farm truck with the 305 that my grandfather purchased new. As a kid I GREATLY underrepresented the torque... it was just a big truck with a small V6. Still have it today although the front end suspension is completely wrung out and parts are unobtainium (different from the same year Chevrolet).
Seagrave and American LaFrance were fire apparatus manufacturers, so those engines mostly went into fire engines. I've actually been in a V-12 powered '64 Seagrave engine that was still in service in the late 80's.
A local volunteer fire department used to have a 1960’s cab over GMC water tanker truck. Had the V12 gas engine. They said it did well into the early 2000’s but they eventually replaced it.
You could also find these in early Minuteman ICBM carriers, I have a Twin-Six 702 pulled from a retired carrier that has been holding down the corner of a shop for many years.
the huge amount of space between the cylinders helps a lot with allowing huge cooling. Of course, this makes it even bigger than it already would be, but that's not a huge problem in a semi.
I would really like to see one of these built using modern techniques, cam profiles and fuel injection. Not really to make outrageous power but to increase efficiency. Power increase would be a welcome side effect. IMO
I think its key to longevity is the low power output. If you made it make twice the power, it would last less than half as long. Like a 2H landcruiser engine, itll do 1.5m km no worries and you can abuse it often and it wont mind, miss some services etc... All good. But it makes 70hp... Make it make 150hp and it lasts 200,000 if you are meticulous about oil and filter changes, dont spend long times at full power, let it fully warm up before hard use etc.
Another interesting thing about the GMC motors is that most if not all of them have governors on them. I think that's the only gasoline motor vehicle that I've ever driven with a governor. I believe in the owner's manual, it actually talks about revving the motor to the governor between shifts.
International v549 in 70s school buses had governors on em. I know of 2 right now in generator applications. Huge gutless thing ,only runs a 75kw gen at 1800. They did the job ,but what a heavy tank.
Those are some impressive specs for the time, especially considering the reliability constraints! It seems on par with the modern natural gas powered 9L inline 6's used in modern city buses.
This thing with some equal-length long-tubes, reground cam, solid roller lifters, a bit of head work, and a couple Holly Dominators with some modern ignition... Imagine THAT bad boy in your hot rod. Or better yet put it in one of those racing fire trucks or something, lol.
My 1969 GMC 5500 grain truck has the 305C V-6. I bought it 31 years ago with a blown head gasket, rebuilt the beast, and it's given me no problems since but It needs valve adjustment annually. The lifters aren't hydraulic and the clearances close up- probably due to today's unleaded gas. It's hauled a lot of firewood at 60 mph and many, many gallons of gas.
GM 3800 in. 40s was and still is industructable...some made for trucks in Michigan. My uncle worked at the engine plant...he is dead gone....3 years...at age 101...Ww2 veteran
I love low revving, high torque petrol engines. I think such engines are underrated, particularly for "daily driving" situations like making quick passes, or accelerating out of a turn or from a dead stop. Arguably, a lower revving engine is more idealized when throttle response is crucial and top speed is irrelevant, such as heavy traffic or curvy roads.
I tend to agree with you. In our cities I see no need for dual overhead cam and four valves per cylinder. That's an awful lot of added expense in the cost of a vehicle. Now if I'm going to take my car and race the Indy 500 I want the four valve overhead cam for sure. My car just needs to get me from one stop light to the next and run the a/c in the summer and heat in the winter.
@1:08min. The 305 GMC v6 engine was actually quite popular on the salt flats beating land speed records before the more common v8 started to show up on the junkyards (source David Freiburger)
637ci engine has a 5.125 bore and a 2.75 stroke Drag racing engine builders should have used this platform for designing their blocks with a bigger piston so we can have more power at the top into the race track in my opinion
The 702 is the true embodiment of "No replacement for displacement"! I would say could you imagine what it would do with a turbo, but then I remember it is a low-RPM engine, so it would never see the full benefit of inducted boost.
The V-12's were used on irrigation wells here in So TX. Especially if you had a "natural gas well" on the farm. Used to be common around Pleasanton, Tx. I had a "305" v-6 in my 66 GMC.
In my opinion, the one and only down side to an engine like this is simply the fuel consumption. everything else is great! super simple, any basic mechanic can service and maintain one, pretty much nothing to fail, way over built. I have the GM 502HT crate engine in a K30 chevy with a tremec TR4050 and it pulls amazing!
They made a 637 v8 that was used in busses as well as making a few of these engines diesel. They had suffixes that designate high output or industrial or diesel etc
The toroflow diesel? this this 702 v-12 looks like its built far stronger than most diesel, the huge bore spacing would make for a sick 2 stroke conversion.
These were the most over square engines GM or anyone built in the 60s. The low rpm coupled with the short stroke kept the piston speeds way down, very important to long engine life.
I worked on these engines for years; our fleet had a significant number of V12 GMC tractors with single drive axles and a pneumatic tag axle for the load weight. You had to be very careful starting them if they ran out of fuel, as they would backfire through the intake flame arresters. I was a tech for the transport company mentioned in the video.
A v8 and some diesels were also derived from that big block v6. Honestly that v6 and this v12 have got to be my favorite sounding v6s and v12s (that are American made)
The GMC V12 was built for the missle mover truck. The driver laid down kind like some racers. When I was going to college, one of my classmates was a missle transporter. I do not remember why the government wanted to use a gasoline instead of a diesel. In 1968 or 1969 all of the GMC missle transporter trucks were scrapped.
That's some fine engineering , purpose built rather than component failure warranty turn around . And when trucks were trucks and not soccer Mom rigs .
Drove GMC V12 powered semi trucks, hauling groceries. Only used on local routes because fuel consumptions was horrid. 1 1/2 mpg empty, 1/2 gallon per mile loaded. Refilled after every trip, I was shocked even then. Also very little power, that could not be hurried.
Wow the bore spacing on the v6 is crazy!! I knew about these engines but have never seen one in real life. I have seen plenty of the ford FT v8 engines that competed with the big gmc v6's. And have seen many of the ford 370 and 429 industrial engines.
😶😶 what an enormous chunk of heavy metal 😮 .. sounds a bit weird somehow, mean without doubts but to me not like i'd expect a V12 to sound like. Dunno exactly how to describe but without knowing and looking at it, just from its sounds while in idle, i'd probably thought it'S a V8 gargling around. Like those Ratrods with that engine, would love to see (and hear!!) them go full throttle 😆
Great video!!! Not too many people even know about the Jimmy V6’s, much less the rare V12. Great engines but as you mentioned, heavy and almost zero aftermarket parts.
Found one of these in South TX running a compressor on wellhead gas. Had been sitting for years, but still rotated. Wish they would have sold it to me.
Someone left engineers and machinist unsupervised in the same room again.
The engineer's heart is usually in the right place, it just takes a little machinist intervention to make it possible.
@@k20nutz we appreciate your work
@@b1646717 and we appreciate a good challenge!
And we're all the better for it! Packard also had a v12 made from two v6s and called the twin six as well.
You should see the 2-Stroke Detroit Diesels in the 1950s they made a v12 then a V16 with 2 V8s bolted together.
Longevity and serviceable.
The forbidden L words of the modern age.
My favorites as well
3800Series 2 were pretty good in consumer vehicles just everything else was not that great \..
@Stickey Sickness Correct.
Now,
Run that past a couple more times.
It's corny, I know.
@Stickey Sickness What are you talking about?
(L)ongevity
(L)serviceable
Yeeessss!!!!
There are 2 sides to longevity. In the oldern days testing how much each engine part needs to take was quite limited. So parts were sometimes much much stronger than they needed to be. When computer simulations became a thing it was much easier to design the parts just about as strong as they needed to be. So cheaper materials like plastic could be used instead of steel as well as less material in general and an overall smarter design. So today with ever advancing simulations cars are made cheaper than ever and with the market being extremely competetive that means in comparison cars are more affordable than ever today. In return they break more easily.
I remember during my auto parts days, a customer rebuilding a 305 v6. We had to break out the old dusty catalogs, but were able to find him bearings and gaskets! He was as surprised as we were!
Peugeot 305 V6? (Best French V6 ever)
@@toyotaae86trueno most likely 305 yank units
@@toyotaae86trueno gm 350 v8 derived v6 is what it is if I’m not mistaken
@@captain1334 That's a 262/4.3l
Never heard of a 305 V6
I guess there was a 305 v6 shown in this video
I had the old 305 V6 in my GMC. The parts stores guys always corrected me, no sir the 305 is a V8 from the 70s....Nope, it's a huge V6, think it used the same size pistons as a 454. I totally rebuilt it, 30 over pistons, cam reground to a modern profile, heads shaved .080 to bring compression from about 7.7 to 8.2, ported the manifold to fit a holly 500 2BBL, changed point to electronic ignition... Yes would have been cheaper to buy a 350 but boring.
If I recall correctly, valve rotators were a $50.00 option on that engine. A neighbor of mine bought a GMC pickup new in '65, or '66 when I was a kid, and that truck ran into the 2000s with never any engine troubles whatsoever.
And it's probably still faithfully running to this day.
@@davef.2329 I did a front crossemember swap also, one from a later model like a 78 will bolt right in. Easiest way to get disk brakes, like $125 for the whole X-member with suspension and brakes.
I couldn't agree more,a great and really over built engine. Those who know truck engines and know what they are supposed to do love them
@@NewFurCat L?
My complements to you for an amazing video. The GMC V6 is the single most under appreciated engine. Paired with the legendary SM420 transmission with granny first gear, its simply amazing. It's a true technological marvel. These engines were so well designed they burned virtually no oil. Take it from a person that owns one.
Thank you for the comment!
I agree entirely. My father worked as a plant manager for GM back in 80's and early 90's. Since then, through a couple of businesses, we've collectively owned fleets of gm v6's and small-block v8's and some diesels though we mostly go with Cummins for that.
Regardless, the v8's get the job done and are workhorses - but the v6's are the unsung heroes. I don't think I've ever seen one straight up die before the rest of the truck became unusable, and we were never kind to them in the field. They fit the perfect role in a supervisor or manager SUV or a people mover: good power so you'll rarely get stuck, good MPG over the v8's, and you can still tow a decent amount with them in a pinch! Can't tell you the number of times we saved leaving a trailer on site to potentially get stolen just because we went with V6 administrative vehicles over vehicles that could never tow.
@@ReggieGeorge probably saw the engine in my 92 sierra wt come off the line… 340k miles and only kicked out because i didn’t realize i had a hole in my radiator until it was too late
@@g_kamikazi wouldn't surprise me if he did. The motors NEVER quit, the only issues were cooling related.
We still have a handful of them in farm trucks at our farm where we never get rid of anything we just park it. have two of our trucks still running with v6s. our dad's 67 Jimmy Farm pick up still down there it runs too just got old need new front end parts.
2:11 "Longevity and serviceability were the two major factors during its development", later you say it was capable making like 500k miles with minor service. 500000 miles, its around 800000 kilometers. And to think: it was made in 1950 - 70 years ago... Man, this engine was a real state-of-the-art beast!
I love your vids VR, full of engines' history and wonderful sounds. You're a real proper engine nutjob around here. Thanks!
Some of the very best gasoline engines the US ever made were industrial and/or workhorse heavy duty motors for medium and heavy duty trucks. Well known for quality and longevity, a large step up from most of the usual motors they made for light trucks and cars.
Back in those days, cars were built to be 100k mile disposables compared to today. Cars were also much cheaper to purchase back then, and the idea of planned obsolescence was working due to significant leaps in auto safety from the 40s to the 80s in the USA. So, seeing an engine be produced in a time where that was going down makes it extra special.
It's a 1500 lb engine that cranked out under 300 hp, and was run under 3000 rpm. It had a lake for a cooling system, and a west Texas refinery for a sump. It ran a low compression ratio, but had a forged crank, and 4 bolt mains. In short, it was a war elephant used as a plow horse. That's a recipe for longevity.
@@ludditeneaderthal thats the key of it all. there were quite a few other engines made at the time that had exceptional longevity because they were built with low compression ratios and low red-lines. parts just arent subjected to extremes.
@@ludditeneaderthal very similar idea to the Toyota 5vz-fe v6. It's so undertuned and overbuilt it lasts 500k with proper maintenance (some are known to make it to 800k). Similar story with the 2uz v8.
Dad had a couple of 305s in GMC pickups, and talked about the V12 from his days driving truck.
Legendary.
My grandfather had a '68 GMC Camper Custom with the V6. 55 mph (88 km/h) top speed, 3 on the tree, air conditioned with split rims.
And more wood than steel, right?
Back when gmc wasn’t just a trim package, love this old industrial commercial stuff
You should do a video on the Hall-Scott ohc inline six (up to 1091 cubic inches) engines, and the V12 version. These engines were designed in the 1920's and were in production until the 1970's. They were used in buses, fire trucks, dump trucks, boats, stationary pump engines, etc. Way ahead of their time, and quite impressive.
You are correct! I worked at the Canton Ohio plant that was building them in the 1960's . We actually have one still active in a riverboat here in Elkhart In.
Less pistons mean less moving parts friction , more power efficiency . We are moving downward , 12,10,8,6,5,4,3 .....
Once again Visioracer, you surprise us again with something old and new to us. That is an amazing engine. Keep up the great work you do. God bless you brother
You said it Joe. Never heard of these and now I gotta add another one to the list dammit.
I really great video! I didn't know they made a 956 but thought it was possible. I have 2 of these v12s, ive owned 8. I have owned every example of this family, 305s, 351s, 379, 401, 432, and 478s standard and "magnum" (bigger ports and valves) V6 engines and a 637 v8. except for the DH637 and DH351 toro-flow Diesels. Most in multiples. We have ran them from 1965 until now. Repowering many things with them on the farm. Dad, an engineer, fell in love with them while working at a GMC dealership. GMC isn't a division of Chevrolet. Rather, they were all part of General Motors Corporation. Just like Detroit Diesel, Cleveland Diesel, EMD, Euclid, Allison, Frigidaire etc. Chevy was the cheapest brand and for that reason alone became the most popular. My 478 toroflo diesel regularly got 27mpg in a cabover with an 18ft bed loaded. The first thing to do is chuck the timing light in the corner. Pull in as much advance as possible and hog out the jets and power valves until they smoke at full load. Then you have a whole new monster that eats Diesels for breakfast, and uses far less fuel than before. They were nutted for EPA reasons and frequently blew head gaskets and rings from pathetic 4deg ATDC timing and super lean jets. Later ones have bigger fastners and dual valve springs. I have accidentally had a balanced, ported, dual spring 401M with an 850 4bbl on a custom intake to 6300 rpm. They are extremely OVERSQUARE, a 478 is 5.125" bore x 3.86 stroke. A 401 is 4.875 x 3.58 huge pistons short stroke, huge valves (2.25" intakes) and 306deg duration cams made big bottom end torque, so low an electronic tach thinks it died! Then pull to 5k rpm.! Modern "stroker" engines couldn't even be warrantied in this type of service. I had a 1959 305A with 500,000 + miles, pulled it after the truck rotted off of it and. Then it farmed for 40 years in a tractor. It polished the cast iron block beside each rod throw from the oil over the years to a mirror! You won't knock a hole in the block with a sledgehammer either! Most people who got a turbo diesel after these cursed the lack of starting torque, excessive shifting, hard starting, and waiting for boost. Diesel torque is a myth when you tune up a big gasser! Great job!
Holy crap man.
your dad is on the 6066 GMC forum, Marti isn't it?
my pops has the 305e in his 65 suburban. has over 500k miles (rebuilt at 400k) love the engine. i wonder if anyone has boosted one?
@Prowbar yes, he was. Sadly he passed from 2 brain tumors. I became disabled from a non cancerous one a year before. Sold the farm and moved. Major communication issues caused almost all of that to become scrap. Even what i kept out was accidentally scrapped. But I still have two 702s and a few Detroits. A friend has his massey 1100 with the 478 in it. And a 401m we modified. Got some 305 boat anchors. Toroflows gone too. Saaad! Allisons gone too. Thanks for remembering!
@@Cletrac305 very sorry to hear that, I wasn't aware of that. As far as GMC engines go, I'm currently building up a 478 (non magnum) to replace the tired 305 in my '65 1500. I'd be interested in hearing what modifications and tricks you and your dad performed on those engines. I have implemented a few myself already. If you want, send me a private message through the 6066gmc forum. My name on the forum is Prowbar as well.
I'm glad I'm old enough to have been around engines like these.
Thanks so much for making this video. I've always loved the GMC gasoline engines and lusted after the v12. We've had a couple of the 305 V6 is on the farm. One thing that I've always thought is interesting about that engine design is that they are very large bore and short stroke. It's the exact opposite of what you would think you would build for a torque producer. But, it absolutely works. They are extremely turkey motors that will pull at a very low RPM.
Air cooled aircraft engines are the same way, huge pistons ,shorter stroke.
Pops has a 65hp Continental in his 46 luscombe.
65hp @2300 and it's 170 cubes.
Nobody ever gave a torque number , but on paper it's around 150.
And it'll never turn over 2800-3000, that's screaming!
They had a 75 and 85hp version ,the 85 had higher compression ,but to jump from a 65 to a 75 it's basically adding timing and revving it a little higher , I think the 75hp rating was at 2500rpms.
75s had piston squirters too,and that was added in on his 65,but he left it set at the 65hp spec.
Large bores make room for large valves, and efficient airflow throug the engine.
@@thomaskarlstrom4815 not really. You don't want huge valves for low rpm high torque engines, big valves means low intake velocity and bad mixture in the combustion chamber.
And the stuffing too
I'm pretty sure RPM is governed primarily by airflow, pertaining to both the intake plenum diameter and length. It's quite similar to port tuning on a subwoofer: given the same diameter, the longer the plenum or port, the lower the RPM or turning. Peak torque resides at whatever RPM causes sound to resonate within the plenum, thereby inducing greater airflow through the intake valves. The sound wave literally slams into the port just as its opening at peak torque RPM. The short stroke was mainly to minimize piston speed and maximize the engine's longevity. A longer stroke would have just meant an even lower redline RPM and untenably long intake plenums.
Something to bear in mind is that when these engines were common fuel prices were relatively low and stable. Gasoline in Pittsburgh was 20 cents per gallon, diesel was 15 cents. The concept of turbocharging diesels wasn't thought of in the 1960s, during the development of the interstate highway system, and diesel trucks were pigs on the hilly two-lane U.S. highway system. A friend of mine's dad drove a 1959 gas cabover Ford until the Arab oil embargo, then he went to a GMC crackerbox.
I was always told relative to inflation and other prices, gas was cheapest in the late 90s when I started driving. It was common to see $1.20 a gallon in California where I was and under $1 elsewhere.
Another guy that doesn’t convert those fuel prices of long ago for inflation. It was never nearly as cheap as so many people try to say.
Why do you think “economy”cars that were easier on gas. came about back in the ‘50s?
@@joemonstermaker4784 True, gas has always been relatively expensive. The only reason people drove gas guzling monsters was they had extra money because everything was cheaper than today and there were less things to spend money on. No games, phones, ect.
I predict this will flip again. With diesel significantly more expensive than gasoline, emissions regulations killing diesel engines, and advancements in gasoline engines that allow them to be more efficient. I think we'll see large gasoline engines make a come back.
What a gorgeous engine. Everything was better back in the days 🙃 Great video as always 👍
Yes, 4 MPG, I wish we had that now :P
@@the_kombinator well with an upgraded fuel system you can get that to 10.
What a beast. The bore spacing is insane compared to ordinary engines.
That would make for a killer 2 stroke conversion! I could cut any port pattern i wanted to there.
I worked on a few of the V6s back in the day, but I never saw the V12. Thanks for the fascinating content.
My pleasure, Keleigh!
I am one of the fortunate still working a big block V6....478 Magnum in a '68 GMC dump truck.. I have several spares and even a diesel version. The best damn gasoline truck engines ever made!
How good was the 637 v8?
@@jlo13800it was probably as good as the V6's and the V12. They are quite rare as by the time it replaced the V12 (1966 model year) the switch to diesel was just beginning in the medium duty market. Fire trucks seemed to be where most of them ended up.
I'd love to fine one.
@@turbo8454 the twin six is a very emotion engine and it will make insane HP Per CID 2 stroke if you are happy. This alloy nickel block was designed by craig iron head heyward which is CGI high nickel will weaken if you are sad! If you are Happy its tensile strength is 235K psi but if you are sad is less than 80Kpsi! the fracture toughness goes down when you are bummed out! So pet it gently!
@@turbo8454 i fucking hate this 4 joke 702 and you can take a plasma cutter to it like any 4 joke stroke!If it dont run oil injection and run in multiple positions i have no use for it. 850 rotax anyone turbo
4000white
My wonderful Dad was the owner of a small family run trucking company in Rhode Island, from the early 50’s, till the teamsters put us out of business in 1981. In the beginning Dad specified International R190 Black Diamond gas engines six wheeled trucks, to haul 20-24’ refer bodies to haul meat, from the Boston Markets into R.I. Under grandfathered rules. But when the trucks aged Dad was forced to save money in able to grow the fleet he chose GMC 7500, 8500 an 9500 six wheeler straight trucks with 20-24’ refer bodies. All powered with 351/5 speed in the 7500’s up to the 401/5 speed w two speed axle. All GMC V6 big blocks. He also had one 5500, with a 305 V6, plus one with a V6 diesel version we called “The Shaker”, because of how it would shake at top rpm. But the gas V6’s all ran for over 200k before their first rebuild!
I drove the V6 with the "granny gear" 4 speed for a gas company in the late 60s. It idled so slow, I was able to flick it into low gear without crunching, without using the clutch.
I’ve been watching your channel for years and cannot help but comment how impressive your channel has become. The clips used, the flow of the script, the production details, every aspect of your channel production has come so far. Your English, too, has made huge strides. Congrats on your growth! You deserve every view and new subscriber.
Thank you very much, Mason!
Valid points...all
I assume 4mpg was working under load, for the 60s that isnt too bad. The Diesel 6 wheeler i drive at work is 5.6mpg. And its $6.07 a gal of Diesel. MPG has gotten better. But you would think it would be MUCH better then what it is. Weight takes power to move, and energy. Be it battery or fuel. The instant mpg on the volvo 18 wheeler i drove would go down to 1.5mpg on bigger hills with loaded truck and trailer.
I would assume not. From what I've heard of its contemporaries, like Ford's 8.8 liter V8 Super Duty from the 50'-80's, was that they could haul anything, but fuel economy was usually closer to 3 MPG when doing work. Consider, too, that the way they kept heavy duty motors in those days running cooler was to also lower compression. Heavy Duty versions of the same motor actually LOST compression (usually dropping from 8:1 to 7.5:1) and were more inefficient.
Good motors from Ford and GM, but I don't thin they were very efficient. We could get 10 MPG out of a 292 V8 in a F600 from 1958, empty. Which is impressive. But still....
@@kingduckford i got a 366ci 6.0L V8 hybrid it gets 23mpg around town 32-34mpg on the highway the battery is bad too
it's just a combo of the transmission that helps put the numbers out.... at 40mph it's barely at 1000rpm at 65mph it's at 1400rpm
If manufacturers would finally switched to opposed piston diesels that would probably be about 8-9mpg or more... they demoed a 270hp pickup that got 37mpg combined city / highway. which is frankly double what pickups usually get... and that was without a hybrid system burning gasoline and not diesel. Achates power look them up... at least the goverment saw the value and is funding cummins to build a tank engine based on this.
I remember seeing this engine for the first time up in Napa, Idaho back in 1987 in fact it is still there at the wrecking yard on display
I ve seen the GMC v6 . And I know they can run at low rpm. At idle you cam almost count the ignition cycles. But they were reliable and strong. But never knew the v12 engine existed that was derived from the v6
there is also a v8 that was derived from the v6, they are quite rare but they do exist. 637 cubic inches.
Best line of gasoline truck engines ever designed. Coupled with an SM-420 transmission and a 5:14 rear end and it was unstoppable with a wonderful soundtrack!
I remember when the V-6 was everywhere. When I was a child I remember my uncle's old packer style garbage truck had one, and a logger across from where my father used to go fishing had one that was kind of loud.
But I always have remembered the sound of them compared to V-8s or any Detroit Diesels.
Could scrappers go to garage from restoration ?
Video Idea: The History of the GMC Big Block V6. I think it'd be an awesome video cause there was different sizes of the big block V6
We have a Seagrave fire truck in our town. It has a V-12 in it. I used to put a sound system and PA system on it every Christmas for the kids. Our firetruck is awesome.
glad you're bringing attention to these
One minor quibble: GMC and Chevrolet are both divisions of General Motors. GMC is not a division of Chevrolet as stated in the video. In the era of this engine, there was very little in common between the mechanical components between GMC and Chevy.
The village where I live had a 702 equipped pumper in the fire truck fleet and I had to replace the twin disck clutch on Christmas Day, alone, early 1980s, in the fire house. No room to maneouver due to the water tanks, a Christmas I shall never forget.
I worked at a truck company in the late '60s/early '70s that had a couple of GMC V6 pickups/work trucks. They also had a lowboy with a GMC V6 powered winch. I never knew about the V12 though. They also had a White Cabover with a 327 for a spotter truck in the yard. I only drove it twice, I think, and then it disappeared.
I had a 1966 3/4 ton GMC pick-up with the 305 V6 it was a torque monster.
A family friend had a Ford 3/4 ton pick-up with the 390 V8 he needed to take some stuff out to the coast so we loaded both trucks up. We stopped at the truck scale I had about 500 pounds more on than he did... on the hills I could climb up his without shifting out of 4th gear. He was down shifting on most hills of any grade. I wish I still had the old girl.
Wow, thanks for this video. I had seen a 305 v6, but never knew about the v12. I had heard from the son of the owner of the v6 that with enough weight, the front wheels would come off the ground from the torque
Mco VEHICLE CHALLENGE !
Happen to have a bit of knowledge of, and experience with this " LITTLE ENGINE " !
While it was obviously a conjoined twin-six design, it was an amazingly smooth running engine ! When in proper tune, it was nearly impossible to hear it running !
The " Blastolene Brothers " out of where else but California, built two absolutely gorgeous albe-they freaky custom design projects, they were then, and continue to be to this day, absolute torque monsters bringing the words
" Made in the USA " some hardcore pride ! 🇺🇲
First time I ever saw one of these was at a car show. Some guy from Virginia had one in a replica of an old Bugatti built on a truck chassis.
You have persevered in your field and today this reveal of the V12 GMC surpasses expectations. My compliments for the research and presentation you have put together. Your work is becoming very engaging finally. Your English speaking has improved vastly over time also ! Bravo Mr.
Jack, this pleases me a lot. Thank you!
All valid points & thanks for pointing that out
My 2006 Duramax LBZ has only 20 Ft/Lb more at the same RPM as this V12. Pretty impressive.
I thought the same thing, but this thing is almost twice the displacement 😂
Never knew this beast existed. Great video!
I learned to drive twin stick and got my CDL in a 1965 C65 GMC 10 wheel dump with a 327 in it.
1:38 the face only a mother could love. Thumbs up you slackers
👊😄
I grew up with a 1961 GMC 4000 farm truck with the 305 that my grandfather purchased new. As a kid I GREATLY underrepresented the torque... it was just a big truck with a small V6. Still have it today although the front end suspension is completely wrung out and parts are unobtainium (different from the same year Chevrolet).
I love simplicity
Seagrave and American LaFrance were fire apparatus manufacturers, so those engines mostly went into fire engines. I've actually been in a V-12 powered '64 Seagrave engine that was still in service in the late 80's.
A local volunteer fire department used to have a 1960’s cab over GMC water tanker truck. Had the V12 gas engine. They said it did well into the early 2000’s but they eventually replaced it.
Would love to see custom 4 valve heads with just the 478 style pistons and the stock stroke, custom rods and pistons.
Thank you for showing the credit! Im definitely looking at these vehicles later!
Really good video, thanks for putting this up and sharing the knowledge! 💪
You could also find these in early Minuteman ICBM carriers, I have a Twin-Six 702 pulled from a retired carrier that has been holding down the corner of a shop for many years.
Thank you for posting about this fascinating engine family.
the huge amount of space between the cylinders helps a lot with allowing huge cooling. Of course, this makes it even bigger than it already would be, but that's not a huge problem in a semi.
I had no idea they made this V12 engine, thanks for putting this together
I owned a 63 GMC 1/2 Ton pickup with one of those V6 engines. Good engine.
As much as we Brits poke fun at the Yanks, I'll admire their commitment to building the most ridiculously enormous engines out there until I die.
I would really like to see one of these built using modern techniques, cam profiles and fuel injection. Not really to make outrageous power but to increase efficiency. Power increase would be a welcome side effect. IMO
if you added fuel injection, you add an ECU, and it will never be long lived again.
I think its key to longevity is the low power output. If you made it make twice the power, it would last less than half as long. Like a 2H landcruiser engine, itll do 1.5m km no worries and you can abuse it often and it wont mind, miss some services etc... All good. But it makes 70hp... Make it make 150hp and it lasts 200,000 if you are meticulous about oil and filter changes, dont spend long times at full power, let it fully warm up before hard use etc.
Another interesting thing about the GMC motors is that most if not all of them have governors on them. I think that's the only gasoline motor vehicle that I've ever driven with a governor. I believe in the owner's manual, it actually talks about revving the motor to the governor between shifts.
the governor can be turned off
@@punker4Real yes, but you risk blowing it up if you do.
International v549 in 70s school buses had governors on em.
I know of 2 right now in generator applications.
Huge gutless thing ,only runs a 75kw gen at 1800.
They did the job ,but what a heavy tank.
The 351 big block Tonawanda engines used in the Chevy Topkick and GMC Kodiak trucks had governors on them.
@@butchs.4239 I've never heard of that motor before. Was It a GM product?
This is my wet dream come true. Longevity over everything 💪💪💪
Those are some impressive specs for the time, especially considering the reliability constraints! It seems on par with the modern natural gas powered 9L inline 6's used in modern city buses.
I wonder what the price was, and converted to today's inflation.
This thing with some equal-length long-tubes, reground cam, solid roller lifters, a bit of head work, and a couple Holly Dominators with some modern ignition... Imagine THAT bad boy in your hot rod. Or better yet put it in one of those racing fire trucks or something, lol.
There were aluminium block ones too.
There's a company that does that, it's called Thunder V12 LLC. Their engines make around 425 hp and rev to 4,000 rpm.
My 1969 GMC 5500 grain truck has the 305C V-6. I bought it 31 years ago with a blown head gasket, rebuilt the beast, and it's given me no problems since but It needs valve adjustment annually. The lifters aren't hydraulic and the clearances close up- probably due to today's unleaded gas. It's hauled a lot of firewood at 60 mph and many, many gallons of gas.
GM 3800 in. 40s was and still is industructable...some made for trucks in Michigan. My uncle worked at the engine plant...he is dead gone....3 years...at age 101...Ww2 veteran
I love low revving, high torque petrol engines. I think such engines are underrated, particularly for "daily driving" situations like making quick passes, or accelerating out of a turn or from a dead stop. Arguably, a lower revving engine is more idealized when throttle response is crucial and top speed is irrelevant, such as heavy traffic or curvy roads.
I tend to agree with you. In our cities I see no need for dual overhead cam and four valves per cylinder. That's an awful lot of added expense in the cost of a vehicle. Now if I'm going to take my car and race the Indy 500 I want the four valve overhead cam for sure. My car just needs to get me from one stop light to the next and run the a/c in the summer and heat in the winter.
As someone who owns a lot of old pushrod V8s and occasionally drives the wife's Subaru, I totally agree. :)
I completely agree.
I worked at GMC building the V6's in 1968-69. I installed the pistons, I didn't know about the V12.
Saw this engine for sale last week in the Netherlands, crazy but I love it.
Great video and it was a great introduction to an engine I was unfamiliar with until this video. Thanks!
My pleasure, John!
It says twin six, but the thumbnail looks like a straight six. I'm glad you mentioned gas guzzler. It's a good thing you're a rich millionaire.
As the owner of 2 305E's and a 351M and a 351E I can attest to the great engineering that went into this design.
ooooooh the sound of that v12 revving gets my tail a'twirlin' 🦊💜
@1:08min. The 305 GMC v6 engine was actually quite popular on the salt flats beating land speed records before the more common v8 started to show up on the junkyards (source David Freiburger)
637ci engine has a 5.125 bore and a 2.75 stroke
Drag racing engine builders should have used this platform for designing their blocks with a bigger piston so we can have more power at the top into the race track in my opinion
The 702 is the true embodiment of "No replacement for displacement"!
I would say could you imagine what it would do with a turbo, but then I remember it is a low-RPM engine, so it would never see the full benefit of inducted boost.
The V-12's were used on irrigation wells here in So TX. Especially if you had a "natural gas well" on the farm. Used to be common around Pleasanton, Tx. I had a "305" v-6 in my 66 GMC.
Insane engine, this motor GMC created 5000 units! And this engine put it on in the Pacific Trucks! Really nice truck to hard work
In my opinion, the one and only down side to an engine like this is simply the fuel consumption. everything else is great! super simple, any basic mechanic can service and maintain one, pretty much nothing to fail, way over built. I have the GM 502HT crate engine in a K30 chevy with a tremec TR4050 and it pulls amazing!
Great, now I want one of these too
They made a 637 v8 that was used in busses as well as making a few of these engines diesel. They had suffixes that designate high output or industrial or diesel etc
The toroflow diesel? this this 702 v-12 looks like its built far stronger than most diesel, the huge bore spacing would make for a sick 2 stroke conversion.
These were the most over square engines GM or anyone built in the 60s. The low rpm coupled with the short stroke kept the piston speeds way down, very important to long engine life.
Hydraulic lifters from a 1953 Cadillac Bel Air… OK whatever you say, Einstein
I worked on these engines for years; our fleet had a significant number of V12 GMC tractors with single drive axles and a pneumatic tag axle for the load weight. You had to be very careful starting them if they ran out of fuel, as they would backfire through the intake flame arresters. I was a tech for the transport company mentioned in the video.
I have a 305ci 6 in my barn, no idea where it came from or what I'm going to do with it?
Find you a old c65 or c30 and make it just a good ole truck. Wont be fancy but will be neat. Could also make a generator or compressor as well
Paint it up and put a piece of glass over it for a cool coffee table. 🎃
A GMC V6? This is the first time I've seen it. And a GMC V12. It would make a good generator engine, the V12 I mean.
Great find, never heard of this!
I never knew and been a car guy all my life even working on several old dump trucks with the 401 v6
A v8 and some diesels were also derived from that big block v6. Honestly that v6 and this v12 have got to be my favorite sounding v6s and v12s (that are American made)
The GMC V12 was built for the missle mover truck.
The driver laid down kind like some racers.
When I was going to college, one of my classmates was a missle transporter. I do not remember why the government wanted to use a gasoline instead of a diesel. In 1968 or 1969 all of the GMC missle transporter trucks were scrapped.
That's some fine engineering , purpose built rather than component failure warranty turn around . And when trucks were trucks and not soccer Mom rigs .
Drove GMC V12 powered semi trucks, hauling groceries. Only used on local routes because fuel consumptions was horrid. 1 1/2 mpg empty, 1/2 gallon per mile loaded. Refilled after every trip, I was shocked even then. Also very little power, that could not be hurried.
This is amazing, I had no idea this existed!
Excellent information, keep it coming and thank you 👍🏼
Wow the bore spacing on the v6 is crazy!! I knew about these engines but have never seen one in real life. I have seen plenty of the ford FT v8 engines that competed with the big gmc v6's. And have seen many of the ford 370 and 429 industrial engines.
I had a few 60° V6 GMC gas motor s.
They made these into toroflow diesels also.
Good motors .
IHC made a 749cid Truck engine.
😶😶 what an enormous chunk of heavy metal 😮 .. sounds a bit weird somehow, mean without doubts but to me not like i'd expect a V12 to sound like. Dunno exactly how to describe but without knowing and looking at it, just from its sounds while in idle, i'd probably thought it'S a V8 gargling around. Like those Ratrods with that engine, would love to see (and hear!!) them go full throttle 😆
I saw my first 305 V6 @ a car show, here in Australia on Sunday.
Great vid! been watching a long time your vids are very informative
Glad to hear it, Dave!
Great video!!! Not too many people even know about the Jimmy V6’s, much less the rare V12. Great engines but as you mentioned, heavy and almost zero aftermarket parts.
One of the least known series of American engines. And one of the best.
Found one of these in South TX running a compressor on wellhead gas. Had been sitting for years, but still rotated. Wish they would have sold it to me.
GMC made a 637 cubic inch V8 in those days as well, just a monster.
I have never seen that V12, that was pretty damn good