Was wondering if anyone knows the differences between the 4.3L block and the E55 K block in regards to structural integrity and tensile strength? Are the blocks the same material or sleeves different etc? Basically I am trying to figure out how the E55 K block can withstand so many LBS of boost and compression if they are both open deck M113's?

 

This has taken a little digging, but I found some info in the 2003 US press kit. 2003 was the first year for the (then) brand new SL55. MB states ‘nearly all the mechanical components from basis 5.0-liter V8 have been modified significantly’. It then proceeds to list changes to the long block: Main caps, bearings, crankshaft, pistons, oil pump, cylinder heads (larger intake and exhaust ports), cams, double springs for the valves, and ECU changes (to support the Kompressor). Surprisingly, they skipped the rods, which are different on a 55K.

It makes no mention of either the 55K block being made of a different material, changes to the sleeve manufacturing process, or the method in which the blocks are cast. In fact, it repeats verbiage from the 2002 press kit regarding how the M113 430 block is made. Regarding the 55K main caps, they must be different, but I don’t see a part number listed. The bearings and cap bolt part numbers are listed, but not the caps themselves. Main caps are included with the 55K short block. As an aside, I’ve never seen a part number for a 55K bare block. I have the part numbers for the 4.3 and 5.5 non-K bare blocks, but not the 5.5K. However, I can only seem to find the 5.5K part number for the factory short block. This presents a problem in determining whether the bare blocks (except for the caps) are different between the 55 and the 55K. If the caps are only available with the blocks, those are very expensive caps.

In an effort to see if there was any difference in the manufacturing process between the 4.3 and 5 liter M113, I looked at the 2001 press kit. I chose that kit because both the S430 and S500 were offered that year. Other than size, the kit doesn’t list any differences. Then again, they don’t say much about the entry level S class engines.

In the 2003 press kit, it says ‘the CLK500 replaces the CLK430 and uses the same 302-horsepower 5.0-liter V8 as the larger CL500’. In discussing the 5-liter M113’s manufacturing process, they repeat the exact same things that were stated in CLK430 section of the 2002 press kit.

Oh well.

 

The same thing Im coming across also, no real info on the differences in the casting of the blocks and how they strengthened the actual K blocks themselves.