plz help me, i am running a b20v on 13lbs of boost and want to lower the boost alittle, if i lower the wastage spring would i need to re tune the car? the spring i have is a 13lb spring, but if i put a 8lb spring would i need to retune it?

 

You should be able to lower the PSI on a turbo car without needing a retune, you just shouldn't RAISE the boost without at the very least doing some street tuning/data logging.

If you make 13PSI of boost at redline then obviously you're making 0-12PSI of boost through the rest of the RPM band. The car should already know how to behave at 8PSI.

 

Depends on how good the tune is. If it was only tuned along the curve you get with the 13psi spring and at WOT, then parts of the fuel map may need adjusted when running lower boost pressures at WOT. The ideal way to do it is run a small 7-8psi spring and tune it on wastegate only, then add a boost controller to increase to the desired boost level, tuning at small increments as you turn it up. This way the fuel map will be complete.