It has been said many times in this forum that these engines are in fact the same engine, but with different degrees of tuning, C230K having the highest boost and C180K - the lowest of the 3.
Now, I just checked the MB Germany website and did a comparison of the three: turns out, they all have different compression ratios:

C230K - 8.7
C200K - 9.5
C180K - 10.2

It makes sense since their boost pressures are different, but doesn't this also mean that their heads are different?

 

I would guess that the difference in compression ratios is due to the piston designs. That would be a far more economical solution than the alternative. The M271 was all about saving money, so my hypothesis would fit

 

I didn't catch these data before but with 8.7 CR does it really require premium gas (high octane) for the C230K? Normally engine with 9.1 or higher would require the 93+ octane.

Am I wrong ???

 

This would be true in case of N/A engine - forced induction changes the picture.

 

comparison chart for calculating effective compression ratio for supercharged engines...

http://www.goodvibesracing.com/Compression%20Ratio.htm

Most likely they keep the effective comp ratio similar in all the 1.8 engines using a piston change as already stated. The higher comp ratio allowed with lower boost gives better efficiency; fuel mileage, throttle response and power can be optimized for each boost level.

Just throwing boost at a C180 is gonna cause a big can of worms to be opened. Max boost will be lower than a C230 can handle so power will be limited by that. If a lot of boost is run, most of the cal would have to be reworked; spark pulled out, fuel added to maintain temps due to the lower spark. It would be relatively fat and lazy compared to a C230 and never reach the same power level without better fuel being used.