exterior wise, they are almost the same. 180sx zenkis and chukis came with half clear half amber signal lights, and they came with optional side skirts and rear valences that weren't available here in the US. 240sx zenkis and chukis did not have side skirts or rear valences, and their turn signals are just amber. The last generation of the 180sx, the kouki, was not released in the US. It came with a more modern front bumper and complimenting side skirts. The rear valences remained the same but a rear spoiler was added and the taillights were changed to the famous "kouki tail lights." Engine wise, the 180sx zenki came with a CA18DET, while the chuki and kouki came with an SR20DET, blacktop/redtop. 240sx zenkis came with the SOHC KA24E and the chukis came with the DOHC KA24DE. The KA is often referred to as the "truck engine" since it was also used in the Nissan hardbody truck. OH and the 240sx is left hand drive while the 180sx is right hand drive

They are a different car