if hes got the stock injectors at 80-90%, hes only at 220rwkw.. stock internals are fine for that.
1st guess would be that the new BOV is leaking air.. would cause a:f ratios to go mega rich and missfire (as well as lovely black farts out the exhaust). check the tension on the BOV spring. Im not too familiar with the SSQV, but im guessing you have to set the spring tension for the amoutn of boost your running.
either that, or you've made a tiny leak somewhere when installing the BOV, and its letting air out under boost causing the same problem.