My argument is for the importance of needing to calculate that in your considerations. That way you know "what" you are looking for. If I dig back in my thread on my mTDI build into the mk1 (as I don't have it memorized at the moment...was a while ago), I have the CC measurements for the stock TDI pistons. Also, between the 1.4, 1.9, etc. TDI's I do not believe that the combustion chamber size within the piston itself changed.
For instance...
1.2L TDI
bore 76.5mm × stroke 86.4 mm
CR= 19.5:1
and your 1.6 TD IDI is...
bore 76.5mm x stroke 86.4mm
CR=23.5:1
the 1.4 TDI (I believe as discussed moves out of an acceptable range bore wise of course...
So, at the moment...the 1.2 pistons are some of the best to work with idea wise and a probable solution. Given the fact that the compression ratio of the 1.2 is in line with the 1.9 TDI, you may not have alot of work to do CR wise, but the calc would be good to have if someone had some 1.2 pistons and the deck height and piston protrusion between the IDI block and the TDI block would effect the CR overall...and more so the "squish" volume than anything...which will contribute to how the motor will run overall characteristically. The interesting thing to look at on the 1.2 would be the valve reliefs and whether they stay the same or "switch" like they do on the 4 cyl TDI's. (i.e. cyl 1/2 are the same, then 3/4 mirror image the valve impressions of 1/2). So, there would be some machining of the valve reliefs but it wouldn't be alot.
Oh....wait...i have the answers to that. Bottom view of the 1.2 head...
compared to that of a pic I pulled of my build ...this is a 1z/AHU head...not from the same exact angle...but I did rotate the above imagine so the front of the head is facing the same direction as this one...
So guess what...there is an answer there...buying 2 Cyl 1/2 pistons from the 1.2 engine and 2- Cyl 3 pistons from a 1.2 will give you the correct orientation for the valve relief for the 1.6 TDI project (utilizing a 1z/AHU TDI head) as well as the orientation of the combustion chamber...
You would need to know the wrist pins sizes and accomodate the tapered rods that the 1.2 pistons will have, but the 1.6's in theory could be used (possible rebushing of 1.6 rod may or may not be needed) to accomodate. It def would be nice to have a 1.2 piston and rod to look at...
Or from there...its finding through the various other DI engines out there on the market what "could" work.
However, in some of the other considerations (wasn't Renault mentioned back a few pages) regarding pistons...it would be "who" of anyone thinking of...considering something along those lines to CC those units and see what the CR would be (before you even start) considering in the calculation the bore that you would need to have in using these in the 1.6 block (while also considering your rod bushings, wrist pins, etc) as DI combustion chambers differ between manufacturers... and the placement of the combustion chamber and the valve reliefs on the piston. All differ when looking at different pistons
A custom piston is almost going to be needed to make things work correctly but it shall be interesting to see if someone can get ahold of 1.2 pistons for an idea or two...
You do have something to start with...
Joe