different part numbers. You can use Si, HF or 88-91 LS integra (both D16A1 + B18A1) ignitors in a 91CRX. The OBD1 ignitors LOOK pretty similar but I wouldn't go trying them. I heard that there is an ignitor for one of the CBR600 bikes that is considerably tougher than the standard ones and that it is a bolt on, but I've yet to try to figure out which one.
