On these pistons both the deck height and the volume of the dished center affect compression. It could be the piston is designed slightly different. A lower compression has the advantage of less preignition ant the melted pistons and burned valves that go with it. If you really want that slight extra power consider Total Seal gapless piston rings.

Dennis

Sent from my Windows Phone
________________________________
From: Tom Lambas
Sent: 4/27/2012 9:10 AM
To: vanagon@GERRY.VANAGON.COM
Subject: piston deck height 1mm low - OK to use?

I just put my first piston in (not german) an found the deck height to be
1mm low. This is a 2.1 with the original crank & reman rods.
If I go ahead with using these pistons am I likely to have any problems? I
know power will be reduced with the lowered compression, anything else?
Has anyone here tried it? The manufacturer has kindly offered a refund or
exchange but says many people use them with no problems - seller says the
same.

Thanks, Tom