P31 vs a SLS...what are the differences...
 

why does the SLS make 563hp vs the 481hp....is it software or what?

I dont get it...

Different cams, throttle bodies, exhaust manifolds allow the engine to breathe more efficiently. The M156 can flow a lot more air/fuel but remember the C63 engines are tuned for emissions and economy not just hp.

Other small things like the dry sump oiling saves parasitic loss of 20 hp. The ecu in the C63 is limited to only about 90% throttle so ecu tuning can only help so much without improving air flow.

The C63 has the M156 as we know, the SLS has the M159.