Welcome from Blighty....
Larger bore throttle body gives 23% more cross-sectional area, allowing corresponding substantial increase in air-flow capacity.
Combined with the other mods you mention, it's no surprise that the later engine is able to deliver more power. The stronger springs are needed if the valves are larger (and presumably heavier) and if they've raised the red-line. Previous one may have been compromised by valve spring resonance. Raising engine speed while maintaining torque leads to more power.
"Torque is the size of the bang. Power is the number of bangs per second" - Keith Duckworth, co-founder of Cosworth
MB will have needed to re-map the ECU to take advantage of these modifications, while at the same time complying with tighter exhaust emissions regulations (Euro 4 to Euro 5). Also would have needed to raise the rev-limit to accommodate the new 'red-line'...
You may be able to unleash some of the power benefits by simply changing the mechanical bits, but I'd say it's likely that some kind of re-map/re-chip is in your future.
Swapping the ECU for a later one may be an option I guess, though that may depend on how the immobiliser/security system works.
Glad to see someone here can anjoy the information presented. I thought more would of interest considering Im preseting the mechanical difference that comprises the huge leap in power of what is otherwise the exact same chassis and powerplant starting in 2009. Im amazed that the attitude is generally more alouf... as in... "eh, something happened... don't care what". I expected that from the non-SLK owners... but you guys. Im taken aback.
As I stated originally, my ecu has been equipped with a total remap. An ecu swap is in this case not only totally overboard and overly complicated but unecessary with such ready access to tuners here in the US.
To answer your question, the remap is not enough and it is infact the nuts and bolts the compromise the engine's ability to crank out 40more hp/torque and at a 700rpm increased rev-limit.
My ecu tune aka air/fuel remap provided a bump from 268 to 284hp. This is obviously much more aggressive than anything MB would have ever provided, but even then theres still much to be desired. I will relate the general enthusiasm for nothing more than car care and maintainence to the fact your SLKs supply a more effective power to weight ratio as well as the 3,27 gearing as opposed to the 2.82.
I was a bit mistaken about finding more information on the technical side from others who may have researched before me, but I'll be more than happy to provide results of this transformation. I must admit before I go that I will not be going near the crankcase and have no desire to gain 5% hp due to one greater point in compression.
anyway, ive rambled on enough.
i have access to a number, but am working with one stateside tuner in particular to remap my ecu. he has already done so in stock trim and will have no issue doing so after addition of intake manifold and throttle body. after all, it takes no more than correctin the a/f ratio. a properly placed LM2 will reside in an exhaust bung and record the latest a/f numbers as the ecu learns what it will on its own. OE Tuning, as they're called, will go back and correct it (lean it out most likely) for the optimum results.
I didnt realise that ecu tuning/remaping was such a foreign concept here?