I did some research for std G16B pistons and came back to have 12.3cc dish.
I shall assume following ....
Head gasket is 1.2mm compressed(5.16cc).
G13B head chamber volume is 30.9cc(from working out CR of 10:1 std).
Std Vitara piston is 0.6mm shorter(2.65cc)
So I did some working out and I came to this conclusion.
To get 8.5:1 we will need to machine off 0.6mm from the block(decking) to take out 2.65cc.
head gasket have to be taken off(5.16cc)
doom of piston(12.3cc)
So actual chamber volume need to be reduced by 30.9-24.34=6.56cc
This means we have to take off 1.5mm off cylinder head. Again assuming it is a perfect circle chamber shape....and it's not....
Can I take off may be 0.5mm off pistons and the block without valve clearance?
Do you think we can machine off more 1.5mm off G13B head as well as 0.5mm of block and pistons?
What do you think guys?
If you want to use them on a 1.3 engine, use 1.3 16V SOHC pistons from a G13BB, they have a smaller dish. Keep in mind that these calculations can and will be differ if you measure the actual head and cylinder volume with some engine oil. We do a lots of calculations before we bought K543M755 Wiseco pistons to achieve a 8.49:1 CR in our 1.6 DOHCs, only to get around 9.5:1 CR after we put together the parts. BTW, we realized that 9.5:1 is even better, and you will not have as much turbo lag, like in VAG TSI engines, 10:1 CR with 0.7-0.8 bar of boost is common. OK, 8.5:1 can handle 1.5 bar or even more, in the 80's, group B cars with 7.5:1 CR can go up to 2-2.5 bar of boost, but do you really want that much?