Ditch the crappy Powercap and refit the standard Airbox & airfilter box XE's hate airfilters

Remove the ECU chip they run far better with the standard chip in place

Depending on what cams you have this can upset the standard management if they are too lairy, if they are just fast road cams they will be fine.

Fit a decent 4-branch SBD 4-2-1 is rated highly but expensive

TBH you won't gain much past 160bhp+ on standard management and fitting Throttle Bodies will take it to around 190bhp+ but in a big old Bardge like a Cavalier you aren't going to feel the benefits massively