Quote Originally Posted by jfrolang
I can confirm that 90-91 calipers have larger pistons than 88 calipers... but I can't confirm that they're the same size as DA. The rear calipers are the same DA vs. EF, so it doesn't make sense to me that a CRX Si would ship with a 2040 valve and and a DA would come with a 4040. Why would Honda make two parts if the brake systems are the same?
The proportiong valve allows for the weight of the car for stability under extreme braking. The orifice inside the valve itself is larger or smaller, and the spring that allows pressure to pass to the rear brakes is stronger or weaker. The CRX weighs a lot less than a DA, thus requiring a smaller valve.

Answer to the second half of your question can be found here:

http://www.norcalcrx.org/tyson/brakepartslist.xls

-jonathan