While the 8-6-4 was a real disaster, it was pioneering, and GM did (eventually) get it right. Several of their vehicles have cylinder deactivation now, and it pretty much works.
That is not the point. I was used as a test unit at my expense, that is the problem.
The Japs developed and perfected the cylinder cut out system for the U.S. Indy Car series to save fuel while under the yellow flag situations. They were allotted as much fuel to finish the race averaging 1.7 or 1.8 mpg on alky. But they could not use maximum allowed turbo boost and have enough fuel to finish the race. So they came up with the cut out system to cruise around under yellow getting 8-12 MPG and then when the green flag came out they could turn the boost up all the way.
I just say this because Cadillac did not develop it and they certainly could not perfect it, especially during that awful time period for them. Cadillac nearly folded over their stupid engine programs back then, but they did come roaring back with the really nice Northstar V8.
I had an 81 Caddy with the 8-6-4 engine, it was a dog when I bought it, but it already had 100,000 miles on it. My 2011 Chevy pickup has a similar system on it, but works much better.