By on April 21, 2010

In the mid sixties, Cadillac gave very serious thought to replacing its aging V8 engine with an OHC V12. And blog.hemmings finally convinced Cadillac to send them some detailed pictures and more information. Looks mighty production ready, but that air cleaner sure makes it looks a lot less sexy than a Ferrari with a bank of Webers. 

Six prototypes were built in 1963 and 1964, all with a 60-degree bank, chain driven camshafts and hydraulic finger followers. The initial displacement was 7.4 liters, but an 8.2 was also built, which corresponds exactly to the size of the new V8 engine that eventually was built instead of the V12. Various induction systems were tried, including single four-barrel, dual two-barrel, and triple two-barrel carburetors, as well as fuel injection. Output was between 295 to 394 horsepower, and from 418 to 506 lb.ft. of torque.

The engines were planned to make their appearance in the new FWD Eldorado in 1967. Ironically, one of the main reasons they were canceled is because GM drivetrain engineers were still considering a transverse orientation for the FWD system. That would have made the V12 too long. In the end, a longitudinal FWD system was used, which would have accommodated the V12.  So the V12 appears to be a victim of poor GM planning.

One of the prototype engines is now available for your viewing pleasure at the GM Heritage Center.

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40 Comments on “The OHC V12 That Cadillac Almost Built...”

  • avatar

    Too bad that never go off the ground. Another opportunity that GM thew away.

  • avatar

    “appears to be a victim of poor GM planning.”

    BTW can we put that on “old” GMs tombstone?

  • avatar

    Cool engine. Is it a requirement that every GM related post include some sort of dig at GM? Can’t we just enjoy the engine for what it is, an interesting prototype that didn’t make it to production for some reason or another?

  • avatar

    A pity in a way – this engine may have helped keep Cadillac in the upper echelons of regard.

    Cadillacs weren’t just noted for being plush and ostentatious, they were hailed for their technological innovations. This was already fading by the time these V12 prototypes were being built.

    Instead, as Cadillac entered the 1970s, it went downmarket and left the high end to Rolls, Mercedes, et al. and the stingy top-down corporate rigidity (same bodies, same engines, etc.) killed their golden goose.

    • 0 avatar

      You don’t actually think CADDY could compete against R.R / Bentley do you?

      I also love the graphic showing the TWO RUBBER looking belts.. as they cross paths…

      CADDY can barely compete against the GERMANS NOW. Audi is already eating MB/ BMW’s lunch, and doing it with VW Corp backing.

      Caddy is almost as pointless and CONFUSED today at it was 20yrs ago.
      The model to move up the chain doesn’t serve its purpose, especially when there are lower tiers in disguise.

      • 0 avatar

        A little late to the topic, but it bears mentioning that as late as 1970, Cadillac was easily equal to Rolls-Royce. The Silver Shadow was a heavy, cantankerous beast with insanely complex systems. A Fleetwood (for instance) was comparatively simple, much more reliable, worlds easier to work on and repair, and constructed to as high a standard as the cars from Crewe.

        The only things you’d give up in a Cadillac are the Connolly leather, real wood, and foreign exclusivity. You’d gain more space, better styling, and service at any corner gas station.

        As far as proof — try and restore a Rolls and a Cadillac today, both 1965 vintage, both with the same miles and wear and tear. You’ll see which car stands the test of time!

    • 0 avatar

      My point was that when Cadillac was building engines of larger than V8 displacement, many of their cars were the equal of RR or Bentley.

      When these V12 prototypes were being built, Cadillac had nothing left in its stable that was the equal of them, and as the 70s dawned their last window of opportunity closed.

    • 0 avatar
      Mark out West

      Accazdatch, you don’t know your car history, that’s for certain.

      Rolls Royce used the GM-sourced slushboxes and Harrison air conditioning equipment since the 1950s, since they couldn’t improve upon it for the “World’s Best Car”. Their 6.75 liter L401 aluminum V-8 was patterned on Caddy’s V-8 of the early 1950s, by their own admission.

      Caddilac WAS the world standard in the 1950s.

  • avatar

    Some potential problems:

    The dual forward-pointing distributors would have ingested airborne water.

    The engine would have suffered from overheating.

    The transmissions would have suffered early deaths.

    Customers would have cursed GM for ruining great ideas, and it would have ended up as a TTAC Curbside Classic, like the Jaguar XJS V-12 did.

    • 0 avatar


      Have to disagree with you (I owned several 1960s-70s Cadillacs):

      If anything, the existing upward-pointing distributor (relegated to serving only as the upper bearing for the oil pump driveshaft on the V12) on the conventional engines would take in more moisture, especially when the points-adjusting window faced forward. The rubber seals on the wires would have easily kept any water out of the towers, and having the cap facing into the source of the moisture is far better than moisture hitting it sideways.

      The transmission would have been unaffected. Their existing V8s had similar horsepower and torque ratings as the V12.

      Overheating? Why? Same displacement, more cylinders. If anything, less chance of overheating as there is more surface area inside the engine around the cylinders for the heat to transfer into the coolant.

      Oh, and one last thing: I WANT I WANT I WANT! This would be a street-rodder’s dream engine! You’d have a mob around your car just to see it.

    • 0 avatar

      Oh, and one last thing: I WANT I WANT I WANT! This would be a street-rodder’s dream engine! You’d have a mob around your car just to see it.


    • 0 avatar

      “You’d have a mob around your car just to see it.”

      +1 again. I remember seeing this loooong-nosed rod in Rod and Custom a long time ago with a Cad V16 engine.

    • 0 avatar


      I’m not really analyzing the design from an engineering perspective; I’d crowd around to see one, too. However, I did have a horizontal distributor in a 95 Stratus V6 (Mitsubishi engine) that had constant moisture problems (but it was transverse).

    • 0 avatar
      Mark out West

      “The dual forward-pointing distributors would have ingested airborne water.”

      Didn’t on the BMW M70/M73/S70 V-12s, of which they made over 50,000 that had the same setup driven off the nose of each camshaft.

      “The engine would have suffered from overheating.”

      In the BMWs, both V-8 and V-12 shared the same radiators. No problems whatsoever.

      “The transmissions would have suffered early deaths.”

      Ditto, same transmission behind the BMW V-12s and V-8s. I certain an old GM TH400 could easily stand the torque.

      This engine is a remarkable precursor to BMW’s efforts in the late 1980s and looks very similar. And to those who question “Why a V-12”, drive one sometime – you’ll understand instantly.

  • avatar

    one of the main reasons they were canceled is because GM drivetrain engineers were still considering a transverse orientation for the FWD system

    It would have been perfect. Wider is always better.

  • avatar

    Very cool. Just as well they didn’t build and develop it. 1974 might have been even worse than it was if Cadillacs were stuffed with these oinkers. The spark plug wires look like they might melt atop the exhaust manifold in that first pic.

  • avatar

    400 HP, 500 foot-pounds of torque, 8.2l V-12 in a FWD 1967 Eldorado would have made for some interesting handling. No wonder they never built it.


  • avatar
    bumpy ii

    Sometimes I wonder what happened at GM in the mid-60s that killed off the last bits of forward thinking in the company. Up until 1965 or so, GM had plenty of progress-making ideas like this, but after then it seems like they just decided to give up and build BOF RWD pushrod V8s until the end of time. By volume, they’re *still* doing that (in North America anyway).

  • avatar
    bumpy ii

    Also, why does it have a generator *and* an alternator?

  • avatar

    And to think, if GM had built this, in the 70’s they would have been positioned to build the first 12-10-8-6-4 engine in place of the blame 8-6-4 engine they built instead.

    If nothing else this would have made for a very noticeable piece of chrome trim on the fender announcing this fact.

  • avatar

    one of the main reasons they were canceled is because GM drivetrain engineers were still considering a transverse orientation for the FWD system

    It would have been perfect. Wider is always better.

    Wonder if their V12 would have been much wider/longer than the Lambo Miuras?

    If it were longitudinal it would have been OK I guess.
    If they had done it would made Cadillac looked good. Able to keep up with the Jones.

    The V8 in old Rolls then were not all that sophisticated, with either 6.25 or 6.75 Litre. They were OHVs, cam in the valley.

    Only V12 exists then were Cavalino Rampantes. It would greatly enhanced GM then.

  • avatar

    A FWD V12–holy torque steer, Batman!

  • avatar


    Cadillac did V12 and V16 production engines in the 1930s.

  • avatar

    Actually, I think it was a good decision not to build the V12. The V8 made just as much power, probably weighed less, and was much more compact.

    GM made lots of poor decisions, but this wasn’t one fo them/


  • avatar

    You can safely assume that, had this engine gone into production, GM would’ve installed those damn nylon-over-aluminum timing gears on the ends of those two camshafts. The resulting devastation to whichever side’s valve train experienced the first timing gear failure would have been epic. And expensive, no doubt.

  • avatar

    I wish they would have built it. Then maybe my 68 Eldorado would be WORTH something.

  • avatar

    What would have the oil capacity have been? 12 quarts? (Northstar V8 is something like 8 quarts).

    • 0 avatar

      If anyone chooses to answer this question then could they please explain to me (if you know the reason) why oil filters on Northstars are the size of a jar of baby food?

  • avatar

    This was the kind of product that would have made Cadillac a distinctive brand. Would it had been perfect? No. But everyone would know that Cadillac had something different and special. It would have forced Ford to create something different and special too. By the time of the first oil embargo in 1973, we would have seen this engine modified and then put into hiatus until the market re-accepted it by 1981.

    Mazda crashed, due to it’s Wankel. However, they kept it for their most expensive personal car. From there, they developed it and with it, Mazda developed an image which today works in it’s favor.

    It isn’t necessarily the fact that the V-12 would have had issues, because every engine has issues. What matters would have been how a V-12 would have lifted Cadillac out of the ordinary – which is what a Cadillac is supposed to do for the extra thousands you pay for them at their dealers.

    Instead of going this route, Cadillac decided to dummy-down their car line and parasite off of Oldsmobile and Buick. This kind of thinking was prevalent during the 1960s. American society believed it could produce a classless society if it tried hard enough. A V-12 flew into the faces of a liberal society’s belief system that everyone could live a rich life. If we take a look at other high priced upper class purchases during this era, we see a similar meme. So, a V-12 would be understood today, but it wasn’t considered futuristic during an era when classic downtowns were being torned down or sheathed in the faux modernity of square Bauhaus boxes.

    Thank goodness that silly way of thinking died for thirty years. Sadly it is back.

  • avatar

    Why would they design this engine for a front wheel drive car and then cancel it due to packaging issues when they had a whole fleet of rear wheel drive cars that this engine would have fit perfectly into such as the deville and fleetwood line. I bet this engine would have been around a long time, especially as a part of GM’s Marine engine fleet. Imagine a 38 foot Cigarette Top Gun with Twin Twelves. Awesome!

  • avatar

    GM is like Budweiser. They *can* make anything. I’ve tasted some AB experimental brews that stand up to anything in the world.

    The reason they (and GM) sell low quality to the masses is simple. They can make it cheap and market it to death.

    GM is famous for shorting the Fiero, fixing it and killing it. There are far too many examples of good ideas from engineering getting squashed in the accounting department. Save the ‘Vette (still with crappy interior) and a few Caddys, they still sell lowest common denominator cars.

    GM CAN make just about anything….they choose not to.

  • avatar

    GM did an aweful lot of experimenting with new ideas up until the late 60’s. Even still there was still quite a bit of powertrain experimentation that took place.

     A lot of the reason why GM, and many other companies stopped was the onslaught of emissions and safety regulations that tied up so many of their resources. However they worked with and developed systems that allowed them to not only work with the regulations, but have engines that produced more power, met CAFE standards and met emissions standards. Cadillac introduced digital electronic self diagnostic engine controls in it’s 1980 models. It’s a system that every powertrain management system built since is pattered after. 

     This engine is an interesting study, and one that maybe should have seen production. It looks to be made of mostly aluminum, which would make it light. A 60 degree V-12 is incredibly smooth, which would have added to Cadillac’s reputation of building powerful, smooth and silent engines. And I think some of this technology was used with the much later HT4100. Note the long head bolts. But there is the question of the cylinder construction. Were they wet liners like the HT4100 used, or were they to use the Reynolds 390 process that used electrically charged silicon particles in the casting process to create very hard cylinder surfaces? that was under development in the big Chevrolet Can Am engines in the mid to late 60’s. It also appears to be die cast. That technique was used with the Vega engine, and later the HT4100.

     The ’67 Eldorado was designed to carry a long engine. Cadillac even experimented with a V-16. The hood was very long to showcase such an engine. However the 472 that was being developed concurrently with the V-12 eventually won out. And it was a very good engine. It was light (63 pounds heavier than a small block Chevrolet), even though it was all cast iron, remarkably efficient (if tuned properly) very powerful and bullet proof durable. That basic engine lasted through the early 80’s in 368 cid guise.

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