I took my recently acquired 8v engine apart tonight to look at the pistons. Just like the 16v engine they stick out above the block by about 0.5mm at TDC. The 8v pistons are flat topped but with a bowl where the spark plugs would stick through. So I guess this is all to do with squish and flame front propogation.
The 16v pistons have a very shallow bowl on them.
Ideally I could have the 16v pistons machined so that they are similar to the 8v pistons. This would involve machining a pocket about 4mm deep. Are this pistons thick enough to tolerate this?