[91civicDXdude]

90-91 integra is a PR4. 6800 rpm rev limit, maps for a 1.8L DOHC.

90-91 CRX/Civic Si is a PM6. 7413 rpm rev limit, maps for a 1.6L SOHC.

all rights and means, a 90-91 PR4 can be used the same as a 90-91 PM6, provided you chip it with the correct maps. the electronics used in both chips are almost identical, so the same chipping method can be used. The microprocessor, however, uses a different codebase in stock form, but this is no problem as you can simply run PM6 codebase in a PR4 ECU.