[tnova]

As for master cylinders, you'll get many different opinions and a discussion on volume vs. pressure as well as stock master cylinders with and without a modified bias spring. The real answer is that it depends on your individual system. Questions to ask:
- Is your pedal firm?
- Is your pedal travel too much or too little?
- Are your brakes balanced front to rear, i.e. will the fronts lock up just a little, a very little before the rears? You need to pull the ABS fuse to test.


The '90 and '91 ZR-1s have the smallest bore master cylinders, 7/8".


On my ZR-1 with Wilwood 6-piston on the front and stock calipers on rear, I could not get the front to rear balance adjusted so the fronts locked up just prior to the rears. I installed a bias valve and it improved but still not enough front brake before the rears locked up. I contacted Wilwood and they advised going to a bigger bore master cylinder from a later model ZR-1, other GM adaptation, or an aftermarket system in order to get enough volume to the front pistons as mine was a volume issue over a pressure issue.


Using an old C4 racers solution, I installed a 4th generation Camaro master cylinder which has a 1" bore. A spacer is required between the booster and master cylinder to keep the distance on the piston shaft to pedal shaft length correct. Others have used Suburban master cylinders. Others have gotten satisfactory results with a later model ZR-1 master cylinder with modified bias spring and/or a bias valve.


So, find an abandoned street or large parking lot, disable your ABS and have someone observe your lockup as you do max braking from about 40-50 mph. Not your pedal feel and travel also. Then call Wilwood since you have their setup. Make sure you tell them what year ZR-1 you have so they know what size bore your master cylinder is.


I'll PM you a document with a summary of posts and solutions on the brake master cylinder.