A car carrying eight teen-agers overturned and landed on its roof, killing two youths, Pomona police said. The car apparently was going too fast on Orange Grove Avenue when it overturned near Ganesha Boulevard, Lt. Bela Laszlo said. All eight occupants, who ranged in age from 15 to 17, were trapped inside for several minutes. Two were pronounced dead after all were extricated from the car. The identities of all eight were not immediately released.