There have been some attempts to put superchargers and turbochargers under the hoods of the 560SEC and 560SEL. Very expensive, and mixed results. I believe their was a Willy MOSSELMAN in Holland who had a company doing it (not sure of that.)
The forum archives and search engine at
www.mbcoupes.com might be worth checking for more information, that has been discussed quite a bit there, it is a performance oriented group there.
What is your rear diff, is it a stock 2.47. That is what the stock 560 SL came with... A first gear start and a 2.82 or a 3.07, would give more low end grunt for sure. A 3.07 or higher would I think you'd rev a lot higher at high and top speeds. Carl Genberg of Bergwerks in LA owned a SEC with a 2.82 and the first gear start, and boy could that thing take off.
Also, whatever modifications you contemplate, is there a way to be assured there won't be a droning sound at 65-70 mph?
Are smog tests a worry? Some modifications could be extra legal in your state? ( Or is it for Off Road Use Only
?
Also, engine bay and hood clearance is a real issue to address before you even start. Gee, I have more questions than answers for you (sorry)
Can the motor even take the stress of turbocharging and superchargers:Again, I don't know. Would you need J & E pistons etc.?
K & N filters are supposed to get the air in faster, but they don't filter quite as well as stock, is the downside, so a little more dirt and airborne crud could get into the motor. That's why I would forego them.
You could get a little more performance with a good set of mandrel bent headers, and a wider exhaust system, and lose the exhaust crossover (it's skinny and restrictive) at the rear of the engine, (is reconfiguring the exhaust ahead of the CAT legal in your state?
Remus mufflers and tips should bolt right in. But don't expect more than 3 hp more with that.
Truth is, the Mercedes V8s, and sixes, any of them, will walk away from a pre 1991 560 engined SL SEL and SEC. The SEC only had 238 hp, the SL had 227. 0-60 times were about 7 seconds, which these days is nothing to write home about.