OK... so I have a '92 Hatch Si which have Arospeed rotors front and rear and a caliper relocation kit in the front. The kit uses larger pads from an Integra GSR. My question concerns the brake master cylinders. I know the parts from the Integra's and Civics are interchangable in some places. I want to replace the small master cylinder in my Civic with a larger GSR unit. Is this possible?

 

if you want to use the integra master cylinder you will have to replace the booster also.
you can use a m/c off a 91 civic ex four door they are 15/16th or i used a 7/8th's off a 95 civic ex and it works great and then you wont have to change the booster

 

Given that your using the same calipers, your piston in the caliper is the same size, so your pusing the same fluid. Don't change master cylinders, all that will do is stiffen up your pedal feel, thus loosing modulation.