Comparison of GTi and Si front suspension¹

GTi	Si

²

GTi lower control arm is fixed to the subframe at two points	Si lower control arm is only fixed to the subframe at one point
GTi lower control arm pivots up and down, but is limited to moving any other way due to the design	Si lower control arm pivots up and down, but has no support in the other directions
GTi anti-roll bar isn't a necessary part of the suspension; the bar is effectively an add on and some people (particularly in rally cars) don't use it	Si sway bar/castor rod is a second connection to the subframe/body, to maintain stabilitiy and take the load off the one fixed point of the Si lower control arm

Si to GTi Conversion

https://www.205gtidrivers.com/forums/topic/175035-205-front-end-conversion-standard-to-gti/
https://www.aussiefrogs.com/forum/index.php?threads/205si-upgrades.133774/

GTi and Si brake line brackets are identical but are in different locations. To convert Si to GTi suspension, it is necessary to drill out the spot welds on the old ones until they come off, relocate them and braze/weld them onto their new location, clear of the struts/droplinks. The solid brake lines need to be replaced and the flexible brake hoses also need to be replaced; GTi hoses are longer (435mm), with a rubber grommet half way along which slots into the strut bracket for support.³

Close-up of solid brake line bracket (after being drilled out):

Pictures below showing the relocated brake line bracket and a GTi strut (with droplink bracket and bracket for GTi flexible brake hose):

205 Si brake line bracket	location comparison	205 GTi brake line bracket