I have a 2001 Sunfire with 16 inch wheels and wanna lower it .
If i lower 2 inch in back how low should i go in front ?

Depends on how you want to lower it but most likely springs so use this info from the Suspension FAQ and go from there...

1- Apex (1.6") - - - (decent choice)
2- B-G Sport Springs (1.6") - - - (decent choice)
3- DropZone - - - (1.7") - - -(they are cheap and on ebay for a reason and they now have changed them to mimic sportlines height wise, but they do sag)
4- Eibach Pro kit (1.4") - - - (Great Choice)
5- Eibach Sportline (1.7F - 2.3R) - - - (Great Choice)
6- Fastco (1.6") - - - (Need Info & Input)
7- GoldLine (1.75") - - - (Nice Firm Ride, Popular Choice)
8- H&R Springs (1.6F - 1.4R) - - - (Decent choice)
9- Intrax (1.7") - - - (Tend to sag to or over 2 inches)
10- MantaPart Sport Springs (1.5" or 2.0") - - - (Need Info & Input)
11- Progress (1.7F - 1.5R) - - - (Decent Choice)
12- Spring Tech (1.8") - - - (Another Ebay mainstay)
13- Sprint (1.8") - - - (Nice Firm Ride, Popular Choice)
14- Suspension Tech (1.2") - - - (Nice Ride, Small Drop)