There are no superchargers for the FWD Northstars so far. XMS is still working on one, but it has been slow going. RSM Racing at http://rsmracing.com/sts.htm has a few mod parts, including larger throttle body, exhaust, and head porting. The claims for head porting have been very good in fact, but of course it is quite expensive. chrfab.com has done quite a bit of work with twin turbocharged northstars, but to put in sand rails and not back into Cadillacs.Jinx said:
Shelby does a supercharger for the 4L Northstar in the Series 1 for around $20K that apparently provides a good boost, and might translate to the XLR.