What bigger engine will fit in a 1990 Honda Civic CRX?

The crx came stocked with either a d15b6 or a d16a2. You could upgrade to a b16a from a jdm civic si-r or go bigger with a b18c from an Acura Integra, both will fit perfectly with a new motor mount kit (usually purchased separately). I dropped a b16a in my 89 civic hatch last year and just installed a greddy turbo and man does it go! Either one would be a good choice, give it a try and good luck.