Take a 1981 911SC and put a 1996 993 varioram engine in it: that's a 911SC-993.
Before:
After:
Or, perhaps more to the point ...
Before: 204bhp in a car weighing 1232kg = 165bhp/tonne
After: 285bhp in a car weighing about the same = 231bhp/tonne
To put this into perspective, the 993 the engine came from weighs 1400kg and thus produces 203bhp/tonne ...
In my defence, I'd like to say that I didn't do this, the previous owner did. He somehow allowed himself to be persuaded that an upgraded engine wouldn't be much more expensive than a replacement original. Which would have been true if you'd been talking about a 3.2, which doesn't require much work to fit. But is definitely not true when you're talking the 3.6 engine from a 993.
£12,000 later ... And even then, he didn't get a proper job for his money. The company that did the conversion fitted the non-varioram ECU, which unsurprisingly wasn't able to properly control the varioram engine, leaving it in 'limp home' mode. More to the point, it would stall when you took your foot off the gas after a lengthy run, and it wouldn't hot-start: not a great combination of bugs.
There were also numerous other electrical glitches, so in the end I had the entire 993 side of the car rewired. The electrical engineer ended up removing over 100 feet of redundant wiring! She now has two entirely separate systems, with two fuseboxes: one each for the SC and 993 sides.
Both original and replacement engines are flat-6, single overhead cam, 2 valves per cylinder. However, 2994cc became 3600cc, and 204bhp became 285bhp.
As I bought the car with the conversion done, I don't have any pics or descriptions of the process. However, there's a company that sells kits for both 964 and 993 transplants, and has some details here:
http://instant-g.com/Products/36Conversion/index.html
A Pelican Parts member has some details of his 964 conversion, together with links to other 3.6 conversions here: