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Seen a post on my Facebook feed about an GMC 702 V12 forsale. Never heard of such an animal, so I had to check out some YouTube videos. That thing is a beast!!!!
They were used in semis for years and then became popular in tractor pull tractors. Basically they were blessed on the 60 degree GMC v6 that GMC used in their light and medium duty trucks in late 50s and 60s.
They pop up on eBay from time to time. Generally in the hands of folks who think they've struck gold with an obsolete and worn-out irrigation engine. Last two I saw, they wanted $7500 EACH for them. Friggin' crazy. I've been "watching" them for years, I've never seen one sell for 1/3 that amount.
GM built 60-degree V6, a few 60 degree V-8 including Diesels, and the 702 60 degree V-12 which is the equivalent of two 351 V-6s end-to-end; except the block, crank, and cam are one-piece instead of pairs of V-6 parts coupled together. The heads and intakes are of course direct from the V-6s.
Yeah, like the W43, someone "discovers" these engines every so often. RPM was limited to about 2400. These were intended to mimic a diesel in medium duty trucks, so similar torque and RPM numbers. They really were just two GMC 305 V6 motors stuck end-to-end with a unique block and crank. They used four V6 cylinder heads and valve covers, and separate V6 intakes, each with it's own carb. GMC also built a 637 cu in 60-degree V8 based on the same V6 architecture (sort of the inverse of the Buick V6) and even did a diesel engine based on the gas engine architecture, over a decade in advance of the Olds diesel. Sadly, GM didn't learn much from that earlier diesel fiasco. Oh, but don't forget the plaid valve covers!
Thanks for the links Joe. I think we discussed the GMC V12 in another thread years ago. Following your last link I noticed that the GMC Toro-Flow diesel had 17.5:1 compression. I thought that was quite low for an IDI diesel, then I noticed that it had turbo charger. Too bad GM didn't learn anything about diesels before releasing the Olds diesel 350 in 1978. I still think it would be cool to score a 98 with one of those!
Nuthin runs or sounds like a mechanically injected 2 stroke Detroit at 1800RPM full load....from the 6/71 six up to the 20 cyl, 20V149s. That's 149 c.i x 20... twin blowers with 4 hair driers on the V series...(twice blown if you will). Torque monsters. Never witnessed another engine handle a full load dump as well as these engines...never even burped at full load dumps just changed in sound a little...in fact, they preferred full load. The 16V149s made up to 4600lb/ft of torque @ 1500, 1600, 1700 RPM! They get bigger than this in the stationary industry but this was my favorite engine to work on and tune.
The GMC 702 V-12 was the last gasp of gasoline engines in heavy duty trucks .
Diesels had taken over much of the industry , but a few operators still insisted on gasoline trucks .
I remember , about 40 years ago , seeing a couple of old GMC " cracker boxes " with 702 V-12's in northern Wis .
They had huge saddle tanks , and fuel mileage was expressed in " gallons per mile ' .
This is a " cracker box "
Last edited by Charlie Jones; Jan 27, 2020 at 10:12 PM.
EDIT>>> SEE MY NEXT POST BELOW >>>#16
The UV549 Roline (Intercrashional) would make a cool rat rod engine too, like the 702 V12. I think the UV401 and 549 Roline International engines were used in school buses and other mobile HD chassis Gas applications, circa 1960s & 70s. This 70KW Onan is NG like most stationaries were. They are (can be) dual fuel.
Stuff this 549 inch big boy in a Gasser, Rat, tow truck or even a Cutlass with zoomies...cool. Do a custom Fit Tech gasoline fuel injection system...blown or hair dried perhaps? That's outside the box. That Mopar with the baby 3-53 series Detroit is cool as hell. Love how he keeps it in the power band while running through the gears.
Last edited by droldsmorland; Jan 29, 2020 at 07:59 PM.
Keeping on track with the original subject matter...702 V12 is a cool rat rod engine...
I am setting the record straight here:
I don't remember the exact Roiline history well. I steered us way off on this one,
The 70KR Onan in the link above is an International (I call 'em Intercrashionals) UV549 Ngas engine, not a Roiline. The manifolds and 45* oil filter housing give that away as International once I woke up. I was losing sleep over it last night feeling something was off....me...So I did some digging today.
The Roiline has the exhaust manifolds on top by the intake. Which should have stuck in my memory. I remember the first time I saw one and how unusual they looked and sounded. Spark plug changes were a breeze. Nuthin like #8 on an Olds with A/C!
See how the internet and bad memories get rumors started without factual data.
I didn't even have Roiline spelled right...jeesh. 40 years and plenty of beers seem to have washed my memory.
I think the roots of Roiline are from the ancient Le Roi engine line. Thus the "Roi" Line...Its pronounced 'roi-LEEN' for us old-timers.
The only time I have seen or worked on one was when it was attached to an Onan Genset long before the Cummins merger. Then gone from history.
The 702 V12 is what sparked me to "remember" the largest small Ngas engine I had a history with. Waukesha makes the Big N.gasers
The Roiline a bunch bigger than the UV549...884 ci...!!!
Can't find a youtube of one running.
Last edited by droldsmorland; Jan 29, 2020 at 08:05 PM.
Seen a post on my Facebook feed about an GMC 702 V12 forsale. Never heard of such an animal, so I had to check out some YouTube videos. That thing is a beast!!!!
Old thread but very cool, the actual owner showed up of one of these. What are your thoughts on this V12. They mention even the small V6 gas got horrible mileage and the V12 is gallons per mile. Bad enough driving our modern pig Diesel Freightliner's with a pup and a 268L tank hauling 33,000L of fuel. Those tweaked Diesel V6 put in those GMC 3/4 ton and 1 ton dually sound pretty good, if the short comings are fixed. I wonder if the V6 Diesel break downs were internal engine short comings or turbo and fuel injection related? Not sure how many Turbo Diesels were being used back in the mid 60's, most farm tractors weren't back then as were many farm trucks. Now try to find a non Turbo Diesel, other than very small equipment.
