My understanding is that MB went with the V6 for two reasons:
1. a V6 is shorter in length, allowing it to be into smaller cars
2. It is basically a V8 with two cylinders cut-off, allowing them to use the same line that makes the V8, thus being cheaper to build.
I remembered reading an old post that Larry Bible contributed on the construction of these M112 / M113 engines:
"My MB Tech friend called the other day to tell me that he had one of these new high tech engines apart if I would like to come by and see it. I made the time.
The engine was actually the v8 version, but everything is virtually the same except for the extra two holes. The car had been in a wreck which busted the oil filter housning and it lost just enough oil to cause some lower end problems.
This engine is an absolute engineering masterpiece.
Starting at the top, the rocker arm/cam followers look like something from a high buck race car. Roller followers and solid alloy construction. They're offset which makes them look even more exotic. The offset is necessary because of the three valve arrangement, there would be no other way to fit them all under the valve cover.
The liners are some sort of exotic alloy. They have a tan look to them, and after 50,000 miles, you couldn't tell that a ring had touched them. They are fit into the block such that there is plenty of cooling liquid all the way around them, something that would not be exposed with the head off of most engines.
The rods are very interesting. They forge and machine the rods, then break them at the parting line. I'm not sure of the reason. I can see where it could eliminate some machining steps, but I can also see that this would make for a more precise fit.
The main bearing caps and webs are really great. There are four vertical bolts and THEY'RE CROSS BOLTED. This is a racing engine feature. The only other engine that I've ever seen apart that used this technique for incredible bottom end strength was the 427 Ford of the mid sixties. I was told that MB actually started doing this with racing engines in 1948.
I missed the pistons. They have almost no skirt at all. The story on this is that the dual spark plugs which are fired about 40 degrees of crank rotation apart, if I remember this correctly, have minimal rocking allowing for the no skirt design.
The ring package is very low tension, this evidently works together with the alloy liners, the piston configuration and the dual spark plug usage.
As I said before this engine is an absolute masterpiece. It wasn't very long ago, when this technology would have been the makings of a very nice Formula One engine.
Well for those who may be interested, there it is. It was well worth the trip and the time out of my day to see it. Now, I just hope that's the last time I see inside of one for many years. Since mine will be given a steady diet of Mobil One frequently, I hope to keep it off the engine stand for many years."
The entire thread is here:
http://www.peachparts.com/shopforum/showthread.php?threadid=1582&highlight=engine