Mahle pistons cast or forged from SC?

[javaschlava]

I hope you guys don't mind, but I haven't any other good source for this info but y'all.
My tech book from Porsche says 78-81 SC's had either Mahle or Kobleschmidt pistons that were cast.
The 82-83 SC tech book from Porsche says that they still either had Mahle or Kobleschmidt that were cast or forged alloy.
Does that mean they had forged Mahle's in the later SC'S. If so is that what you get now from Mahle in 95mm CIS pistons.
My question really is what is the toughest stock piston?
And what is the disadvantage to using Kobleschmidt if any.
Thanks
Mark

[Steve@Rennsport]

Mark,

The VAST majority of 3.0 SC pistons are cast; Mahle or Kolbenschmidt.

The former were used in Nikasil cylinders and the latter ones in Alusil ones and they are not interchangable.

[tom1394racing]

Steve

I was under the impression that when a piston had a non-circular skirt (ie flat section at the pin face) like the 3.0 SC Mahle shown in the photo below, that it was a forged piston. Conversely, when a piston had a circular skirt like the 3.0 SC Kobelschmidt in the photo below, it was a cast piston.

Is this not true?

3.0 SC Mahle Forged?



3.0 SC KS Cast?

[docrodg]

Not true, cast and forged pistons can be made either way.

[tom1394racing]

How does one tell the difference between a cast and forged piston?

[tom1394racing]

Here's more info on Cast vs Forged pistons

Cast Versus Forged Pistons

Forged or Cast?* Piston Basics!

[JFairman]

A set of forged JE pistons I installed in a BMW motor would ring if you lightly tapped the edge of the skirt while it was sitting upside down with the skirts facing upward on a bench and they were alot lighter than the origonal mahle's

Cast Mahle's would just go thud.

[Steve@Rennsport]

Originally Posted by docrodg

Not true, cast and forged pistons can be made either way.

Thats right.

One needs to look closely at the surface finish (inside the pin boss area) to determine whether its cast or a forging.

One can see the direction of the grain structure on a Mahle forging in places where its not been machined.

[javaschlava]

I think we are getting somewhere.
Thanks for the pictures Tom!
I still want to know if the early SC's had something different than the later 82-83 SC's in pistons, meaning early SC's had cast Mahle's and later SC's had forged Mahle's?
If so is there a part # difference
and if so can you get cast Mahle's or do you now just get forged ones?
Thanks.

[javaschlava]

WKD-422-720-OEM Porsche 911SC, 911 Turbo Factory Spec Book (1978-81)

WKD-423-120-OEM Porsche 911SC, 911 Turbo Factory Spec Book (1982-83)

Here are the books I meant, that mentioned the Cast pistons in 78-81 models
and cast or forged pistons in 82-83 models.
Its in the beginning of the books where they state all the engine facts.

Anyone wanna stab at it?

Thanks Mark

[Steve@Rennsport]

Mark,

While those little spec books are truly invaluable, they are not dead-nuts accurate and neither are the factory shop manuals since both were written before production commenced. Thats why they send out Service Bulletins,....

AFAIK, only the 930's got forged pistons; the rest were simply a mixed bag of what they hand on hand when the engine was built.

[javaschlava]

Dear Steve,

Thanks thats just what I wanted to know. Sounds like Porsche.

Btw what does AFAIK stand for? Forgive the neophyte.

Thanks
Mark

[arrivederci]

Originally Posted by Steve@Rennsport

Mark,

While those little spec books are truly invaluable, they are not dead-nuts accurate and neither are the factory shop manuals since both were written before production commenced. Thats why they send out Service Bulletins,....

No...what Steve offers to the general Porsche community is truly invaluable! You're one of the few that know what's what. Thanks for being there.

(btw, shocks/suspension on my '81 worked great this year, wish I could've spent the $$ for something more than bilsteins)

[Steve@Rennsport]

Originally Posted by javaschlava

Dear Steve,

Thanks thats just what I wanted to know. Sounds like Porsche.

Btw what does AFAIK stand for? Forgive the neophyte.

Thanks
Mark

Hi Mark,

While I'm not shy about picking on Porsche when they do stupid things, its only fair to say that ALL auto makers do the very same things regarding technical documentation. Others simply do a better job,....

AFAIK: As Far As I Know.

[JFairman]

i thought all the air cooled street cars including 930's had cast pistons but i donno...

[Steve@Rennsport]

Originally Posted by jpinkert

(btw, shocks/suspension on my '81 worked great this year, wish I could've spent the $$ for something more than bilsteins)

Good news,....

I'm very pleased that it worked for you. Whenever you wish to take it to another level, I have some ideas,....