Hard brake pedal under boost/Building boost

[Flicktitty]

So i was thinking about some of the problems the car's got while it is parked for the winter, I've been trying to figure out what is causing this issue and how to get rid of it. So i'm asking for help on here.

Car: 1989 Nissan 240sx SE
Toyota 2JZ-GTE / Aristo Auto/ Single turbo etc.

I've noticed when i do a pull and get into boost the brake pedal goes ROCK HARD and i have to pump the brake pedal once or twice to get the car to stop. Same goes for when i have the car in gear and i try building boost with my foot on the brake/gas trying to leave on boost the car makes 3-4psi sometimes 5-6 then the car starts moving as the brakes cannot hold the car.


I had this issue with the 1st swapped car, and again with the new swapped car. The new car has a 1 way check valve in the brake like (OEM Nissan) and new hose going from manifold to the booster. The car is on stock brakes (will be upgrading to Q45 in the next week or two) So how could i make the car have a stock like brake pedal when in boost, and have a brake setup that allows the car to make more boost.

Any ideas?