Mahle Mystery Pistons - Calling all experts

Now that this problem has been solved, I would like to display my ignorance in order to learn something. Assuming the original piston design could not have been located, couldn't the newer heavier design have been easily modified by judiciously removing (grinding, drilling) some metal where it could be safely done, in order to make the weight the same as the original piston?

It appears that the distances from the wrist pin to the top of the piston are identical, and the the surfaces of the piston tops are identical. If the weights are then the same, how can the engine tell the difference?

 

I have a few tidbits of knowledge that may help someone somewhere on this topic. The color dots are in fact diameter grades. The green (gruen) is for dia 80.910 piston in a 81.010 cylinder. Pink (yes pink, "rosa") is the diameter of 80.900 for a cylinder of 81.000. Another point of interest is that the USA part (forging 81P9) has a 1.2mm deeper combustion bowl than the "EU" piston which still usees the 81P6 forging. I am not sure of the differnces in the mass but the EU piston must be greater and definitely has more machining in the inner core of the forging. The larger combustion bowl inthe USA piston more than likely is for a lower compression ratio. Both styles share the same compression height (distance from the pinbore centerline to the crown) and overall height. Another point of interest is that the spacing between the circlip grooves (snap rings that hold the floating pin) was reduced in 1988 by 0.75mm. I don't know why. I hope this interesting for somebody. Till.a.fischer - very familiar with that area of Bad Canstatt. Just for a piece of trivia - the building closest to the Neckar of the headquarters of MAHLE on Pragstrasse was the site of the original home of Maybach. Anyway good luck to all!!!!

 

The numbers I was quoting are from the existing drawings produced in the eighties. Something suspicious is that the "8093" is not part of the part number (as I recall). Unfortunately, I don't have the drawings in front of me (although I do plan to frame and hang in the garage). I do remember being impressed by the fact that the groove widths were very impressive for "back then" - 1mm, 1mm, and 3mm. It also appeared to me that the 81P9 is for USA production and the 81P6 is for EU production. In fact, it is noted in the change revision log of the 81P6 to add the "EU" stamp on the crown in the year of 1988. This leads me to believe that the 81P6 is still used for EU production. I'll post groove height information on Monday. One would think that it shouldn't be this difficult - perhaps part of the mystique.

 

the red and green dot piston is for matching to red or green dot liners when doing assembly/repairs as these are different tolerance ranges ...i have only seen this in late model ferrari's...and only had to deal with this on 355's when the had a blown manifold cylinder damage during a valve job

 

A key point in all of this-the QV pistons discussed in this thread, and the correllation to closed loop, oxygen sensor, LambdaSond 3-way catalysts.

The heat ranges intrinsically required for a duty-cycled driven stochiometric burn-required for a 3-way cat, as opposed to air injection for an oxidizing hydrocarbon affair...better known and Ferrari referenced as "Thermal Reactors"
and the skosh to the fat side needed for a power prodecer such as these Ferrari engines(as a whole)-dictates clearances unknown in their production cycles to date.
Remember, this is also the advent of Ferraris implementation of Nikasil coatings, and of the Stellite process or valves.

Sizing is CRITICAL for effective cylinder sealing, and hence, the gas charge being interrogated by the Zirconium tipped dipole just in front of the Catalyst
There is the ranging issues as been listed by the other posters.
All in "tenths"...important to notice...an order of magnitude "tighter" tolerances that the 2-valve mills.


There is one additional set of markers which I've waited to see if noted here...
the XXX(black letters, usually 13mm in hight)

While much rarer on Ferraris than say....MB, they identify an "intermediate" size not found in any of the regular parts lists....
they are an intermediate "clean up size" for cars that are usually:
problem oil users-as oppossed to oil "burners,"
and
more notably,{in Alusil blocks}, Hammerring when cold(only 45-90 seconds)
While errily disconcerting to the uninitiated, not really a big/serious deal!
More importantly, no real damage occurs if engine is warmed up properly!

{Ask most most 1991-94 BMW M5 owners about the hammerring when cold...merely forged skirts as they begin to expand..}
Power and eye popping performance comes at a compromise...read: street cars...

I used the XXX series on190-16v, M103, M104, M116, M117, M119, and even in 1 M120!

In my own experiences, the real culprits were NOT the pistons-which are magnificent forgings-but in the quirky details of ring design, and application...
I anxiously await the promised information on ring sizing, dimemsions, etc.
If overheated, the rings will lose some-but not much is needed-spring tension, and whilst there might be a measured 0-2% leakdown, there can exist excessive oil useage.
Differentiated from oil burning-which produces the blue, acrid, clouds of "mosquito abatement," so common in the old 250s/275s which have sat in the Carriage House for 5-6 years!
ANY info on ring tension? Angles of sweep, etc, etc?

This has been a GREAT thread!
Please-more....thanks for the additional information on Manufacturers marks..
CIAO!