heads

[1300mk2]

Why would it lower the compression ratio?

i assume the combustion chambers in the GTI head have a bigger volume than those in the 1.6 head.

if the volume is bigger compression will go down, no? if the volume is the same i bow down to your supperior knowledge and crawl back under my stone

[golfvr6]

The compression ratio on the gti head will be higher.

[1300mk2]

if you increase stroke and/or bore size compression ratiowill go up. that's one of the benefits of putting a 2l bottom end on a 1.8 head.  if you are putting a 1.6 bottom end on a 1.8 head you are decreasing the stoke size the bore is the same but compression will go down.

[golfvr6]

Not necessarily.
I think you will find that 1.8GL runs at a lower compression ratio than a 1.8 8v gti.
This because the combustion chamber is smaller on the gti.
So with a smaller combustion chamber, putting a gti head on a 1.6 will increase the compression ratio compared to a standard 1.6.
Depends what you are comparing it with.
I think you meant the ratio will be lower compared to a 1.8gti, it will, but it will be higher than the standard 1.6.
The way to get round that is put 1.8 pistons and crank in the same block, as vw only made one block for 1.6 and 1.8. That will give you 1.8L and with the gti head, the same compression ratio as the gti.