I have a massive shop Vac under my Hood
 

I need Help. This happened before my rebuild and now again. When I first got the car it had no power and had a huge whooshing sound under boost. When i got the car back under light throttle I tried it out, WOW. All the mods were worth it. After about 300 miles it is happening again. No power as the secondary turbo starts to build pressure, and a HUGE whooshing sound. I thought it might be the BOV but I took it apart and it seems alright.

I know that I have to break the engine in so it has all been done under light accel.

Thanks
Steve

its got to be a boost leak, check all of your turbo piping especially the coupling coming off of the ypipe