can i change a 4 door front end for a si front end? has any one done it

 

if you mean a 99-00 si, and you have a 99-00 4door, yes, it'll all fit. you can use the si grill and lip with your stock bumper, since the front bumpers are the same for both cars.

even the optional rear lip from a 99-00si coupe will fit on a 99-00 4door.