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Hello Ozzi! Sorry for a late reply, the original piston to deck height is(if i remember correctly)0,5mm below deck.
With an 86mm crank the height will increase with 3mm(half of the increased stroke), and of cause 7mm with the longer rods.
the original pistons are 46mm high(pistonbolt center to top) and the b200 pistons are about 39,5mm high, but the b200 pistons(depending on type)has a deep bowl in the center that makes it possible to shave them down to the right height.
However, if you use b200 pistons you are limited to maximum 0,060" overbore.
There is also a forged Mahle piston made for VW boxers that is 34,5mm high and got 93mm boresize and is quite cheap too. unfortually it got 22mm bolts, but its possible to just make a new rod bushing quite easy.
With a 93mm bore i would recommend a 75īor a 76ī block because they got slightly thicker cylinder walls.
About piston to deck height, i would recommend a piston over deck height as follows: 0,1mm clearance piston to head per 1000rpm max rpm (ex. 6500rpm =0,65mm clearance).
Remember that this must be calculated with compressed headgasket height.
Then the piston or block is shaved to the correct height.
This will give you a greatly enhanced burn speed, although the distributor curve will need modifying(less pre-ignition at high rpmīs)because the burn speed increases even more by rod,pistonbolt stretch at high rpmīs.
Theese improvements will give you a strong,powerful engine with a improved fuelmileage.
Hope i have helped you some.
DE.Sweden.
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