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Hagerty Employee

Why GM’s V-12 “Engine of the Future” never made it to production

Sixty years ago, General Motors was nothing like the company you know and (maybe) love today. In the 1960s, the firm was well-stocked with the industry’s smartest designers, engineers, sales experts, and division managers. No technical hurdle was too high, no engineering feat too far-fetched, for the colossus that bestrode more than 50 percent of the market and had no Asian competitors to fear. So when someone raised a hand and suggested that a nice, fresh V-12 engine would add luster to Cadillac’s prestige, there was broad consensus and no fiscal concern.


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New Driver

Two other deadbeat GM engines that should have never been built:  GM diesel and the V8-6-4.  

Intermediate Driver

Re: Jag's XK engine (6 cyl) and the V-12, the 6 WAS faster in the early 1960s. But by 1971 when the V-12 debuted, emission and other requirements made it really slow down. By contrast, the V-12 in 1971 was a very fast, turbine smooth engine with a huge increase in torque and hp over the 1970 XK engine, although not much more than the XK was producing in 1961 when the E Type debuted. I have owned both 12 and 6 cyl E's and I prefer my early car, but the 12s were fabulous and a huge step up at the time.

New Driver

Cadillac engine history:


The Cadillac 331 engine that debuted in 1949 was eventually enlarged to 365 and 390 cid, and continued through 1962.


In '63, Cadillac redesigned the engine to be lighter weight, but kept the 390 cid displacement. 


In '64, they enlarged the engine to 429 cid.


That engine became the 472 in '68, the 500 in '70, and the 425 in '77. 

Pit Crew

I own a Jaguar XJS V12. Most of what is said here applies to that engine also. No real power advantage over other engine designs, but a noticeable fuel mileage penalty. But the V12 is very smooth, more so than any V8 I have driven, and has a unique sound. Perhaps those are reasons enough. 

New Driver

"In '64, they enlarged the engine to 429 cid.


That engine became the 472 in '68, the 500 in '70, and the 425 in '77. "


The 429 absolutely did not become the 472 engine in '68.  The 472/500/425 (all 501 series engines) were a fresh design of new architecture and were a far better engine.  

New Driver

"The Caddy 429 was the last of the 50’s engine family, ending in 67. In 68 the 472 was introduced and was a totally new family, 1970 is when they increased the 472 to 501 inches, on Eldorados with the 501, the fender badge said 8.2 Litres. In 77 they decreased the 472 down to 425 and then again to 368 in about 1980." 


Once more, the 472 was increased to 500 cubic inches NOT 501.  The 501 number designates the engine series.  The 472, 500, 425, and even the 4-6-8 368 were all "501" series engines.  This mistake/misconception (whatever you want to call it) has been going on for years and I guess, like many old wive's tales, will continue.   


Love to know what sort of MPG it takes to power these monsters.


Intermediate Driver

It would be interesting to know some of the science behind why these V12s underperformed and drank more fuel

That thing would have looked very impressive under the hood of an Eldo

New Driver

Correction noted.  The 472 was more than a poked & stroked 429, but I would not refer to it as a complete redesign. Many maintenance items were improved and it was slightly smaller in exterior dimensions.  However, it also weighed around 80 pounds more than the 429. 


The 1964-67 429 was a plenty stout performer. I've owned five low-mile Caddys:  '61 CdV, '64 Eldo, '64 SdV, '67 Fleetwood, and a '70 Eldo.  They were all under 30,000 mile original cars, with the '64 SdV being a 14,000 mile one-previous-owner gem.


I owned these cars at the same time, so it was easy to make real-world comparisons.  The 1967's had the switch-pitch torque converter with the Turbo 400 that made rubber-peeling starts an easy feat. 


The 472 and 500 were torquier than the 429, for certain, but my '67 Eldo was very close in performance to the '70.  Both cars were completely stock, and properly tuned.  The '70 would smoke the tires a bit further, though!


I actually preferred driving the '67 Eldo, mostly because its interior was nicer. The dashboard and door panels were considerably cheapened in 1969-70. 


I grew up with Cadillacs of the '60s and '70s, and have logged a lot of miles in them.   

For my money, my favorite years of Cadillac are 1964, '67 and '68.


New Driver


Thank you. That's an interesting factoid. During the period 1971-74 I worked with the 390 blocks daily. Later, still working with the late Lee Muir, I worked with the alloy on an aircraft engine project for 7 years. Have a look at the April, 2019 issue of Victory Lane Magazine for a full description of that program- "When the Can Am flew".  Regarding the Vega, It had  (I think) a bad rap for sure. We felt the problem with the Vega was the open deck which precluded sufficient cylinder stability and allowed the cylinders to "move around", killing the head gasket and ring life. At the race team we had a Vega GT with the Cosworth head from GM as our parts getter. You can  imagine how that car was operated by a bunch of 24 year old Can Am mechanics. It never broke, and I remember it with a smile.