1969 911S piston question

[lopena]

The Porsche PET catalog shows two part numbers for pistons of a '69 911S:

901-103-911-01 for "group 5", and
901-103-911-02 for "group 6"

Can someone please explain the group 5 vs. group 6 distinction to me?

Many thanks, as always,
Alan
NJ

[Jon B]

Can someone please explain the group 5 vs. group 6 distinction to me?

Alan, those part numbers are for one replacement piston & cylinder, not the piston alone.

The "Group 5" and "Group 6" refer to cylinder height groups, the numbers usually marked on the base of the cylinders in a triangle symbol...



Jon B.
Vista, CA

[lopena]

Thanks, Jon!

So, if I'm looking to order a new set of Mahle pistons & cylinders for a bone-stock '69 911S 2.0 do I want the Group 5 or the Group 6?

[Jon B]

Alan,

An engine must have cylinders of the same height group on each bank, in other words 3 matching cylinders per side.

If you're purchasing a set of 6 pistons & cylinders, the specific height group doesn't matter, as long as all match.
If you can only put a set together with 3 of each group, it will be fine, as long as you keep a matching group of cylinders together on each side of the engine.

Jon B.
Vista, CA

[lopena]

I appreciate your help and expertise, Jon!

I'm writing to you from a Greek island in the middle of the Aegean Sea where it is now approaching lunchtime, so it must be 2 am where you are...go to bed!

Thanks again!

[72targa]

Interesting. So Group 6 would be slightly higher compression?

[Frank Beck]

Group 6 would be lower compression; the piston doesn't sit as high in the cylinder.

But you're talking a gnat's ass. The carbon build up on a piston can create "higher compression" than .001" cylinder difference.

[72targa]

Makes sense. Wondering why the factory would go to the trouble of making two castings that are essentially equivalent?

[Jon B]

Wondering why the factory would go to the trouble of making two castings that are essentially equivalent?

Peter, the differences occurred in the machining process.
Porsche probably accepted a 0.05mm (0.002") variance based on cost- to be more precise would have probably cost more, maybe significantly more.

Jon B.
Vista, CA

[Frank Beck]

Peter, the differences occurred in the machining process.
Porsche probably accepted a 0.05mm (0.002") variance based on cost- to be more precise would have probably cost more, maybe significantly more.

Jon B.
Vista, CA

If that's true...
I SURE WISH I was around back in the day to buy all of the "4's" and "7's".

Alan,
Just curious: Where do you plan to buy new 69S P's&C's AND get to have an option on 5 or 6 height group?