I still I have the stock power master brake unit on mine. I was about to convert to vacuum brakes but decided to rebuild the master cylinder and add the ron custom max boost brake module. Since I have done this the car brakes extremly well and I could hold more boost than I ever did. The way the ron custom brake module works is that when it is engaged by a momentary switch it bybasses the stock brake proportion valve and sends alot more pressure to the rear brakes which makes it alot easier to create boost off the line. I have done my best 60ft (1.52) at 9 lbs of boost, but I am sure that I could hold up to 12 lbs or even more but still haven't tried it. The only thing I know is that this brake module works well for me.
3.8VSIX How much mileage did your car have before changing your valve springs. Did you see any performance gain after changing your valve springs.
86 Grand National t-top (59000km)
stock long block,stock suspension, red stripe convertor, te44, smc alk injection, 24lbs boost, 94 octane, hooker cat back with dyno max ultra flow muffers, tomco 30lbs injectors, dynotech stage 4 street chip, thdp, mease 24 row IC, MT drag radials (275/50/15) 3800lbs race weight.
best ET
60FT=1.52
1/8= 7.38
I/4= 11.74
MPH=113
BEST MPH= 114