A V8 with forced induction -how nice !!
I didnt relaise the SL55's were forced induction - supercharged i assume - hence the pulley change.
In my experiece many years ago with Ford RS Cosworths (a wonderful vehicle but lost on our American cousins), standard 204bhp 2litre 4 cylinder.
In the UK the trade in ECU mods was MASSIVE, every jocky with a laptop was a bespoke software engineer!!!
In my experience there are very few 'real' software engineer's out there who have the knowledge to modify an ECU - the variables to consider in the program are 'significant'.
There are various ways to extract power from an engine, the basic principle is pour gas in one end, force a bit of air in, explode the mixture in a metal box -off we go.
The real experts turn these basic principles into an art, they don't simply pour in more gas and wind up the boost. Remember MB have spend millions on software development, some guy in a shed wont better it. Faster is easy, better is not so easy.
YOU GET WHAT YOU PAY FOR - cheap is cheap.
But the right mods are AMAZING, performance improvement is blistering. But remember that motor is unlikely to do 500,000 miles - who cares !!!
Trust me i have changed melted pistons - that ain't good !