E63 vs C63 engine
 

Why does the C63 engine have less horsepower than the E63? Is there only software or also mechanical differences between the two?

Don't be fooled by both of them saying "63". Only the C's engine is an actual 6.3 liter. The E's engine is a 5.5 liter with two superchargers. The C doesn't have a supercharger.

So, they have completely different characteristics.

I think he might be referring to the MY 2007-2011 E63 which share the same engine as the C63, but are rated higher.

The engine is the same, it is software differences as far as i know. Mercedes doesn't want their "cheaper" car to be lighter and have equal horsepower, so they tune the E63 engines so they are rated higher... to sell better.

If you do the same aftermarket ECU upgrade to both engines you will be at the same horsepower I believe.

It's exactly what I'm thinking. Thanks!

Pretty straight forward probably except for the solenoid that control the cams but I guess we'll figure it out some way.

I just bought my self a C63 engine to put in a hot rod so I was a bit worried to lose some horsepowers to the E63 engine.

The main difference is the throttle being restricted in the C63, when your foot is hard on the floor the actual throttle plate only opens around 2/3 of the way (and opens fully in E63, S63, etc.). Aftermarket tuners found long ago how to get rid of this throttle restriction and, along with other tweaks, surpass the power output of the larger models with this M156 motor.

The attached dyno screenshot shows how much power you can gain at higher RPM just by removing the throttle restriction. You can clearly see when the stock tune causes the motor to run out of airflow when horsepower flatlines from 5,000RPM to redline. Allowing the throttle to open fully lets much more air in and allows the motor to continue making power.

Jailbreak's full tune adds even more power and shows significant gains at all RPMs, but this particular dyno run shows how important the throttle plate reprogramming is to unlocking the full potential of the C63. The M156 in the C class is identical to the other models using the M156 and it is only the stock tune that artificially limits power.