I had two of these pumping water. They ran on Natural gas. I was told the city of Chicago started using the 702 on Propane to run buses. The project ran into trouble when they had an explosion.
My 3/4 ton gasoline V8 truck does 2200 at 70, what’s hard to believe about it? That one’s probably geared mighty high or has a modern double-overdrive trans in it (doubtful), though. I think the redline on those engines is like 2700.
Given the torque curve of it, adding a tail-shaft overdrive unit wouldn't hurt, given the redline it sees. And to that, I recall what I've heard time-&-time-again: It's the camshaft & valvetrain that limit the RPMs the redline occurs at. ;)
have you thought to try a diesel tach that runs off of the alternator.? Most of them are 4000 or 5 units and you'd get a lot more sweep. Love your video.
Sounds like it has a good heavy flywheel, reminds me of an old jeep 4.2 they lug pretty good on the low end. Im a GM fan and always have been but just heard of these motors recently. Guess theyre pretty rare.
@@April-r8b My brother was a mechanic for the Hostess fleet. This was the standard engine in a lot of their older trucks. Fuel economy was awful in the inter city duty they were used for. 3-4 miles per gallon.
I love how the 60-degree V12 fits in the width of the narrow truck hood. Now all you need to do is run stacks out the sides, and it will look and sound like a P-51 Mustang!
Maybe, it’s less than half the size of the Packard, no dual stage two speed super charger, no 100/150 octane av fuel, no water injection, might sound like a mini version. Wonder what kind of power this motor would make at altitude with a basic forced induction setup
@@dirtyaznstyle4156 Sadly, the GMC 702 never got much attention from hot rodders. It's about the same weight as a Merlin, but puts out 1/6th the power. How fast you want to go with it depends on how much you want to spend creating custom parts.
@@andyharman3022 Since this engine is basically two V6 engines connected tail to nose, a lot of parts already exist. Rods, higher compression pistons, intake manifolds and heads all come to mind. You are doing custom work if you want a better cam. The biggest problem with trying to hot rod this engine is that the reciprocating mass of the crank, rods and pistons is so great, you can't increase the RPMs much past the factory red line which was something like 2800 rpm. That really limits what you can do with this set up. But if you are satisfied with an engine that can pull stumps all day, this is your baby.
Have one 305 and two 351 in two drivable truck. Great farm and work truck engines awesome torque. By the way they would work at @15 MPG. Try that with a big block anything like my 8.1 Silverado.
You using a 700R4? You may want to use a governor from a 6.2l diesel for that trans, or just weld allot of weight to your current governor so it shifts lower
Cool ride, really cool sound. Thanks, we have been waiting a while for this. Love the dash, now the tack needs little marks to satisfy the cop. Have a great, healthy, new year.
What transmission is being used? It’s a more modern steering column, with the key and all. If a person could find an old 4-speed Hydromatic from back then… I loved the way they brutally shifted.
That's awesome. My friend has the same in his'76 ta, 5000 in first was 80. My 84 C10 has 2:73 and on dyno they would go to red line (7200) because 5000 in second was 138mph
It's 700r4, It's pretty light for the torque, but best I could do at the time. I'll never throttle hard if on pavement, gravel, maybe a little. If the wheels don't slip pretty easy, it will slip the tranny and it's was newly rebuilt.
Can the engine really only rev to 3000? I understand that it is an industrial engine, but they are still usually balanced to 4000+. Although it does have a ridiculously long crankshaft so maybe that is why. What are the torque specs on that monster?
Originally, 650 to 675 depending on compression ratio. They rivaled the Cummins diesel of the day but at 2 mpg in a loaded fire truck, they were a hot rod. These were also used in the Minute Man mobile missile launchers. Brute of a gasoline HD engine.
Ah yes, a giant engine that is way under stressed chugging along in a vehicle that weighs nothing compared to the truck it came in. Absolute perfection!
I used to drive a 305 in a 62 GMC half ton that got about 8 MPG if that thing is as thirsty per cylinder as it was you are going to need bigger LP tank to get on up the country.
I OWNED SEVERAL OF THE V-6 VERSIONS AND ALL BUT 1 WERE IN GMC 3/4 TON 4X4s BUT I DID FINDE 1 THAT WAS IN A 1/2 PIKUP AND IT WAS A FACTORY APP BELIEVE IT OR NOT
THOSE ARE RARE RARE MONSTERS GM DIDN'T BUILD MANY ASWELL THEY WERE INTENDED FOR USE IN SHIPPING YARDS TO MOVE CARGO TRAILERS AROUND TO THE BEST OF MY KNOWLEDGE THEY DIDN'T OR WERNT USED AS HYWAY ENGINES ONLY USED IN HEAVY INDUSTRY
With its original applications, the biggest problem would be a low red line, but it could be done with a different cam profile, forged pistons, and boost.
@@CJColvin Still wouldn't make a lot of difference in the redline. Maybe one of the V6s it was based on. Not every large engine was meant to or can be a rocket.
@@anonymousinc6330 actually I was thinking about that last night as I have access to 3 or 4 V6 . Horsepower sells cars torque wins races. GM built the turoflow diesel engine on top of the V6 block platform. Pistons rods and crank. It was a very good reliables fuel efficient medium class diesel engine. The vortex style Diesel Heads was the reason fuel economy and cold weather and starting was so good in the diesels.
Sounds like a farm truck? Going down to get a bale of hay. Be right back. 1941 called and said, we have a problem and want the design of your engine for a plane.
My C-10 with a 396 n a 700r4 with 3.08's on the ass end gives me 70mph at 2000rpm. But don't let it fool you, the 4spd OD is supposed to save you gas. But it don't, unless you drive like the little ole' lady from Pasadena...
Dude really driving around with NO HOOD ? I'm of a mind when some one' see's my pick up sitting at a light with a hood that's nearly 2 foot longer it's scream's out what the hell's in the thing ? not to mention it looks so much nicer that seeing two silver spray bomb painted air cleaner's that hide a pair of 1 Barrel carbs and some ugly hoses .. But I'm sure your gonna get to the hood part sooner or later maybe you can help me understand why the electric fan is running on a motor that's only 140 .
I had two of these pumping water. They ran on Natural gas. I was told the city of Chicago started using the 702 on Propane to run buses. The project ran into trouble when they had an explosion.
Someone shot your truck 2 times on the right side windshield
68 mph at a but over 2000rpm. That GMC V12 is a torque monster!
My 3/4 ton gasoline V8 truck does 2200 at 70, what’s hard to believe about it? That one’s probably geared mighty high or has a modern double-overdrive trans in it (doubtful), though. I think the redline on those engines is like 2700.
@@The_sinner_Jim_Whitney my truck does 70 at 1700 rpm
@@reuben5274 Most do, mine has 4.10s.
My Ram is 1500 at 70 MPH.
My Silverado 1500 does about 70/75 at 2200
Oh man! I just discovered the big block v6 and v12s tonight. The coolness i am finding! The 637 engines too!
Me too !!!
The big block v6 is pretty cool
I think the big block v6 is the same block as Detroit
@@jeffwain All Detroits were 2 stroke until the mid '80s. So it's unlikely they shared anything with these 4 stroke gas engines.
@@them_damn_rocks1617 yeah i was going to comment that too
I thought the 8000 rpm tach was a bit optimistic ! Cool engines.
Maybe, but he had a mark on the lens with the factory red line drawn in.
Given the torque curve of it, adding a tail-shaft overdrive unit wouldn't hurt, given the redline it sees. And to that, I recall what I've heard time-&-time-again: It's the camshaft & valvetrain that limit the RPMs the redline occurs at. ;)
have you thought to try a diesel tach that runs off of the alternator.? Most of them are 4000 or 5 units and you'd get a lot more sweep. Love your video.
Love to hear it with a nice full exhaust system. Especially if it was built to spec on the lower compression ratio.
Sounds like it has a good heavy flywheel, reminds me of an old jeep 4.2 they lug pretty good on the low end. Im a GM fan and always have been but just heard of these motors recently. Guess theyre pretty rare.
Only 5000 ever made
@@April-r8b My brother was a mechanic for the Hostess fleet. This was the standard engine in a lot of their older trucks. Fuel economy was awful in the inter city duty they were used for. 3-4 miles per gallon.
LOL! sounds like a MERLIN! A company called thunder v12's makes versions of these that can turn 5000 RPM!
How much power in the thunder v12
I love how the 60-degree V12 fits in the width of the narrow truck hood. Now all you need to do is run stacks out the sides, and it will look and sound like a P-51 Mustang!
Maybe, it’s less than half the size of the Packard, no dual stage two speed super charger, no 100/150 octane av fuel, no water injection, might sound like a mini version. Wonder what kind of power this motor would make at altitude with a basic forced induction setup
@@dirtyaznstyle4156 Sadly, the GMC 702 never got much attention from hot rodders. It's about the same weight as a Merlin, but puts out 1/6th the power. How fast you want to go with it depends on how much you want to spend creating custom parts.
@@andyharman3022 Since this engine is basically two V6 engines connected tail to nose, a lot of parts already exist. Rods, higher compression pistons, intake manifolds and heads all come to mind. You are doing custom work if you want a better cam. The biggest problem with trying to hot rod this engine is that the reciprocating mass of the crank, rods and pistons is so great, you can't increase the RPMs much past the factory red line which was something like 2800 rpm. That really limits what you can do with this set up. But if you are satisfied with an engine that can pull stumps all day, this is your baby.
Have one 305 and two 351 in two drivable truck. Great farm and work truck engines awesome torque. By the way they would work at @15 MPG. Try that with a big block anything like my 8.1 Silverado.
Why i see bullet holes
You using a 700R4? You may want to use a governor from a 6.2l diesel for that trans, or just weld allot of weight to your current governor so it shifts lower
Sounds like a WWII fighter plane at fast idle at 60 mph!
2K at 70 MPH, I love it !!! Just a stroll in the park for that engine.
Cool ride, really cool sound. Thanks, we have been waiting a while for this. Love the dash, now the tack needs little marks to satisfy the cop. Have a great, healthy, new year.
I bet that old booger would pull hell off the hinges!
Thank you! Everyone just has cold starts and exhaust sounds, but not a single video of someone ACTUALLY driving one of these.
Here is the first one that he built, it is now in a museum in Boise City, OK.
th-cam.com/video/3Cd0nIdD-8Q/w-d-xo.htmlsi=qZt9PJ4D9VUvj0AB
Runs and sounds great. My favorite was the 283
How did you get the automatic transmission to mate with the engine block ?? This truck must have tons of torque !!
What transmission is being used? It’s a more modern steering column, with the key and all. If a person could find an old 4-speed Hydromatic from back then… I loved the way they brutally shifted.
High gear was about the same as a semi I used to drive, 2100 RPM @ about 68 mph.
Perhaps a direct ratio in the gearbox (1:1). Depends of the rear axle ratio...
I'm running 2.41 "posi" in my 500 caddy powered 81 bandit T/A and she's turning right at 2000 revs at 60 with 265/50/15 tires "25.4in"
That's awesome. My friend has the same in his'76 ta, 5000 in first was 80. My 84 C10 has 2:73 and on dyno they would go to red line (7200) because 5000 in second was 138mph
That sounds awesome 500 caddy's are one of my favourite engines of their era
Is that bullet holes in the windshield?
What trans is this where its only at 2k going 70?
It's 700r4, It's pretty light for the torque, but best I could do at the time. I'll never throttle hard if on pavement, gravel, maybe a little. If the wheels don't slip pretty easy, it will slip the tranny and it's was newly rebuilt.
sweet truck! so that's where my 87 chevys steering column went
A good home
No masks. Really ?
Can the engine really only rev to 3000? I understand that it is an industrial engine, but they are still usually balanced to 4000+. Although it does have a ridiculously long crankshaft so maybe that is why. What are the torque specs on that monster?
The factory recommended 2500 rpm max. About 550 ft pounds torque at 1500 rpms.
No, I guess it would wind 'til it blew itself up with no load. 24-2500 is the factory recommended max. rpm.
Just idling down the road
Lol, you're right.
Military vehicles
"How many lb-ft of torque does that make?"
*"Yes."*
Originally, 650 to 675 depending on compression ratio. They rivaled the Cummins diesel of the day but at 2 mpg in a loaded fire truck, they were a hot rod. These were also used in the Minute Man mobile missile launchers. Brute of a gasoline HD engine.
Most likely a lot more than that slideomatic transmission can handle 😖
Thats amazing, lovely cruising speed for seriously low revs!
Folks...we had to cut the video short due to the catastrophic collision with the ground post you see there, where the video ends.
Speechless. Great engineering accomplishment!
You going to have to get that new liquid to fix those bullet holes and love those old engines good job
I have seen one of these make 5200 rpm aftermarket. Absolutely insane mechanical problem
Odd sounding engine 🤔almost like a cross between a straight 6 and a v..very nice👍✌
Omfg bet u still have pedal confusion.....another thumbs down.
Ah yes, a giant engine that is way under stressed chugging along in a vehicle that weighs nothing compared to the truck it came in. Absolute perfection!
I used to drive a 305 in a 62 GMC half ton that got about 8 MPG if that thing is as thirsty per cylinder as it was you are going to need bigger LP tank to get on up the country.
Pretty Kool!🤗
Sounds like torque!
I OWNED SEVERAL OF THE V-6 VERSIONS
AND ALL BUT 1 WERE IN GMC 3/4 TON 4X4s
BUT I DID FINDE 1 THAT WAS IN A 1/2 PIKUP
AND IT WAS A FACTORY APP BELIEVE IT OR NOT
Almost sounds like a Merlin!
THOSE ARE RARE RARE
MONSTERS GM DIDN'T BUILD MANY ASWELL
THEY WERE INTENDED FOR USE IN SHIPPING YARDS TO MOVE CARGO TRAILERS AROUND TO THE BEST OF MY KNOWLEDGE
THEY DIDN'T OR WERNT USED AS HYWAY ENGINES ONLY USED IN HEAVY INDUSTRY
You don't need a speedo I drove for years with just a tach but it was a stick
wow ,almost 70 mph and barely turning 2000 rpm
Man that is one cool old truck that is beautiful
It sure is brother and that GMC 702 V12 sure sounds like a beast.
The torque!!!!
And now we know what the jeepers creepers guy was running😅
I miss America. The America today really sucks
Love it but hella exhaust leak.
Wait for the comment
Are you sure that fan clutch is working it turns all fully slow
Nice but too bad it's an automatic trans. Kinda spoils it.
has anyone ever tried to hot rod one of these engines? It'd probably cost a lot but it'd be really cool
With its original applications, the biggest problem would be a low red line, but it could be done with a different cam profile, forged pistons, and boost.
@@anonymousinc6330 Don't forget to port the heads and intake manifold as well as adding some headers.
@@CJColvin Still wouldn't make a lot of difference in the redline. Maybe one of the V6s it was based on. Not every large engine was meant to or can be a rocket.
@@anonymousinc6330 True
@@anonymousinc6330 actually I was thinking about that last night as I have access to 3 or 4 V6 . Horsepower sells cars torque wins races. GM built the turoflow diesel engine on top of the V6 block platform. Pistons rods and crank. It was a very good reliables fuel efficient medium class diesel engine. The vortex style Diesel Heads was the reason fuel economy and cold weather and starting was so good in the diesels.
What good is this? Can't even see the car! Waste of time.
fuel economy more like fuel UNeconomy
Sounds like a rattle trap from hell.
I heard from my grandpa thy where hard to tune
Can we get a steering wheel to go with the gauges
You don't have your tech set right
Nice old truck!! Nice sounds too!! Something to be said for simple designs!!
How do you get a tach to work with that?
38 or 39 Chevy truck,??
lol where the hell you find parts at
Most of the motor part are salvaged from other motors
I got a 62 gmc 5000 dump truck with a 305, been looking everywhere for parts all I can find Is camshafts and bearings
Got some tall gears in that thing
Opinions are like buttholes seems everybody has one... this is an epic engine in an equally epic chassis i bet !
Camaros are like assholes. Everyone has one.
Your opinion!!!!
This is much cooler than an LS swap.
Uhhhh. That's a stock 454 LOL
Sounds like a farm truck? Going down to get a bale of hay. Be right back. 1941 called and said, we have a problem and want the design of your engine for a plane.
Beautiful truck...I see that windshield took a few shots..sturdy ole gmc....
Everyone: The ZZ632 Is the largest engine gm has ever made!
The 702: Hold my beer
Thanks for sharing!
My C-10 with a 396 n a 700r4 with 3.08's on the ass end gives me 70mph at 2000rpm.
But don't let it fool you, the 4spd OD is supposed to save you gas. But it don't, unless you drive like the little ole' lady from Pasadena...
What’s it sub 200 hp ?
0:25 are those bullet holes?
Yes they are bullet holes
My little four cylinder will hold 80mph at 1750rpm without an issue. Thanks to a 9 speed transmission.
Not much for RPM huh
Thanks for that.
Not impressed!!!
Have to have a tanker truck to follow up with a 4in. line hooked up with the fuel tank!😆😀😁😂🤣😎😎😎😎
2.41? 2.29?? How tall them back gears bro?
That's pretty cool I can't believe I've never heard of these. Nice video man.
Oh how I wish the blacktop in my county were as smooth as the dirt in yours
American iron.
I'm getting a bit of a Spitfire vibe listening to this.
I was hoping for some tire smoking, it roaring at 3500 RPM :))
sound just like a 4.3 with a rusted out muffler
You are lucky
LOVE it!
Dude really driving around with NO HOOD ? I'm of a mind when some one' see's my pick up sitting at a light with a hood that's nearly 2 foot longer it's scream's out what the hell's in the thing ? not to mention it looks so much nicer that seeing two silver spray bomb painted air cleaner's that hide a pair of 1 Barrel carbs and some ugly hoses .. But I'm sure your gonna get to the hood part sooner or later maybe you can help me understand why the electric fan is running on a motor that's only 140 .
Awesome. Wish I'd seen this 10 years ago
What was the point in this video ? Ihni???
If you have no idea, then this video was made to make little boys ask questions
Back in the day when gas was cheap and plentiful !
Wait.. redline is at 2,800?
I figure that has to be an Allison HT-series (Heavy Torque) automatic transmission.
Sweet, say it with me. Turbos, put turbos.
It’ll tow a double wide over the pass at 70mph
Andy, yes the Merlin sound! I did not associate this. Thanks.
I went a slightly different route.
What happened to the windshield