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RE: Pistons for MC motor needed...
Thanks for the piston site information.
>There's a offset dish in the piston crown for the MC motor.
Don't know which VW motor would use these. The Mahle catalogue
listed the 2 pistons in 81.01mm and 81.51mm and they refer
to the Audi 200 with GV motor up to 87. Seems like there's a
gap between then and the 91- 200. But from diagrams and the
piston here it seems to be the same piston with casting
number 81 P 11 +/KA.
In what way are they high performance? Lighter?
FWIW I had an "AAN" motor piston and rod assembly briefly. There is a
recessed dish in the top of the piston if that's what you are referring to
as an "...offset dish." Scribed in the top of the piston, right above the
point where the two intake ports look like they must dump their charge & the
plug fires (i.e. marked by a dark carbon stain) are the numbers "80.98"
which I believe are the stock piston diameter.
I'd meant to have the piston weighed, but since it was not mine I did not
want to separate it from the connecting rod assembly. I would like to get
approximate weight figures for the "stock" pistons and connecting rod
assembly. FWIW, I have seen 3 connecting rod assemblies out of a small
4-cylinder Lotus engine, one stock, one Carrillo and one a custom forged
billet rod. These, the Lotus rods, "looked" to me to be in about the size
category as the Audi rods, perhaps a little shorter.
I can't recall the exact weights of the Lotus rods, but I do believe I
remembered the differences pretty accurately - the stock rod weighed in at @
800grms; the Carrillo about 125grms lighter and the custom forged steel
billet rod another 100grms lighter than the Carrillo.
I don't know, but I've been assuming that the stock AAN and 3B pistons are
forged, not cast. Its been an assumption I've been making based on the fact
that engine seems to me to be such a high out put motor for it's size, and
being turbo charged it must, "of course" be made of that "stronger stuff."
Heck, but I don't know for sure, perhaps another lister can fill in the
In looking for more information I'm now questioning that assumption, i.e.
forged not cast, based on the fact that the factory (i.e. the Bentley)
clearance spec. for the Piston / Cylinder Wall is .03mm - .0012 of an inch.
Other "general" literature I'm seeing on "high" performance aftermarket
pistons, i.e. "forged" is saying that depending on the alloy used, e.g.
"high" silicon vs. "low" silicon, forged pistons require more "cold"
clearance that the @ .001 of an inch possible with cast piston tolerances.
So, I'm left with still looking for "definitive" info on:
- The stock Pistons - Aluminum or Steel? Alloy"
- Forged or Cast?
- Weights? I.e. Stock Piston; or Piston & Rings; or Piston, Rings &
gudgeon/wrist pin & circlip?
- Weight comparison(s) - Stock vs. J&E vs. Mahle vs. Kolbenschmidt vs. ???
Last, but not least I do have a photo of the AAN / 2B piston if that would
be of any help to you.