i have a 1990 300zx and on the valve covers the hoses that come off of them mine are rock solid and i dont know where to get new ones and i was wondering how much pressure runs through them so i can gauge what kind of hoses i should get or if anyone can help me with finding the hoses that i need

 

There is not gonna be that much pressure. All those lines do is to vent the positive crankcase pressure to atmosphere. In other words, if the air pressure buildsup in your crankcase, the excess pressure would come out to your pcv valves (which are under your upper intake manifold). However, when i was rebuilding my car, i totally deleted this system. I blocked the pcv valves with a hose on it and a bolt on the other end. This made an air tight seal. For valve covers, i plugged all of them except the one on the passenger intake. I connected any hose i could find to it and put a small air filter on the other end (which in my case, i made one out of a fuel filter, nd then cut the housing around it). You really dont need pcv valves. As long as you have a ventilated hose (the small air filter) to allow the crankcase to adjust itself to the atmospheric pressure. Let me know if you have more questions.