Not the old 368ci V12 from the 30s you're thinking of, but a 500ci aluminum ohc version!

I finally came across a good picture of this engine. It was developed by cadillac in the late 60s, and would have replaced the 472/500 V8s, but it was never actually put into production. Check out the 2 separate distributors mounted out front of each cam.

I like stuff like this because it's sort of like a window into the future as it was seen in the past, like relics of a time that never really existed. Anyway, imagine driving around in an early 70s Caddy with the top down like Boss Hogg, except with one of these suckers under the hood:smoke:

There was a prototype/ styling buck made up for it. Think vaguely Stingray body/window treatment, w/a baroque 1963 std Caddy front clip & tailfin treatment, & impossibly long front fenders. Sez here in my "Cadillac of the Sixties" book that they fooled around w/V-12s from 1960 til 1967.They got serious enuff in '63 & '64 that 2 engines were made & installed in '64 Cads. There was also a smaller, 450 CID version. The testing concluded that while they were VERY powerful-400HP, & 500LBS of torque, they weren't substantially better than larger projected V-8s that were also in development. They WERE somewhat smoother. Anyhow, Cadillac elected to go w/the 472 motor in '68, & then the 500 in '70. What COULD have been...(sigh...)

I didn't realize the V12s were being developed at the same time as the 472, I always figured it was slightly after.

I like the engines like the Caddy 472/500 and the Buick 430/455 a lot, they're sort of the last of the big V8s. But I only wish that we got that one more step ahead.

There was another "Skunk Works" project going on at Cad during that era...a 4-door convertible. There was one made in early 1960, to see if it was a feasible project, & because they'd heard their friends over at Dearborn were planning one, too. It turned out to be very do-able, but it was decided to wait until 1965, when the GM "Big Car" chassis was being totally revised. There were perhaps 6 units custom-made by Cadillac in both 1965 & '66 model years, w/maybe 15 or so made in total from 1965-70. Another marvellous "What if"...Lincoln's convertible sedan program died in '67, w/2300 or so units produced that final year. Production was never great, running about 3000 units a year for the 1st several years, & Cadillac was selling everything they could push out the door in the Sixties, anyway. Besides, body engineering was devoted to getting the '65s on line, as well as the Eldorado, which followed in '67. They didn't really need to mess around w/a convertible sedan, w/such a small market...And there was a lot of anti-convertible sentiment growing then-"They're NOT Safe !!", plus the interstates were growing, & its not really a lot of fun being blasted at 70-75 in a convertible...

I had no idea Cadillac had a proto V-12 in the 60's. Pretty cool! I wonder if any of the top dogs had a special Eldorado built with a V-12? I love the '67 to '70 models best.

This reminds me of the GMC 702 CID V-12 which was produced in the 1960's.
I found a youtube video of a restored unit which was installed in a modified pickup truck.

http://www.youtube.com/watch?v=pha8W_AcDaA

That is a crazy looking engine, especially because of the apparent single venturi carb. I bet Jay Leno would like that one if only for parts.

I think those GMC V12s used 2 2 barrel carbs. And that they just used 2 sets of heads and manifolds off of the GMC 305 V6 on them.

I had a 1972 sedan deville 472, a 76 fleetwood 500, and a 74 deville 500, they were torque happy powerful but still got 18 if you drove civil, Mine got 11-12 MPG on school days LOL and I could get half my graduating class in the back seat and trunk, long before birth control invaded its way into the automobile. I do remember getting picked on by a classmate for driving a ship he had a 79 camaro 350 built up decent he stopped harassing me when I passed him with my 472 with all of his cool buddies riding with him during a long distant light to light drag what was funny was after I got a job and a new car I later took my 1984 Pontiac Parisienne 305 V8 for a tune up to him as he then worked for a Chevy dealer, he said man that was embarrassing when you went passed me that way, I said yeh he said now I know better that 350 was quick, but your car had long long legs.

Primary use of those GMC V-12s was in fire trucks. Even though a diesel would've probably been more appropriate, fire departments demanded the "turn the key & go" ability of a gas engine. Most likely got about 2 MPG.

One of the customers at our dealership had a ton & a half GMC truck with the mongo V6 (401?) on his hobby farm. He asked us if we'd rehab it so he could use it for wood hauling, etc...and make sure everything worked so he could actually drive it into town if he wanted. Took over 2 months to track down all the parts...but, man, was he happy! Took 2 techs to lift ONE of those V6 heads.