My old Turbo DAYTONA did that and it was a lil' more impressive, I was running 36psi of boost on race gas, and when I spooled it with no CAT it lit up the steet behind me.....but I was also running quite abit more fuel than you probably where.
Here's a quick low down.....When you run the motor at high RPM's on an EFI Motor and boost is in effect, the EFI will run richer...now, when you let off the throttle aruptably the un bruned gases are going to run through the exhaust system in a ball of flames from the heat enerated from the turbo charger. The only way you can get that much fuel through the exhaust is to run without a CAT converter, or commonly known as a test pipe...as seen in the F&F2 there running propane injected flame throwers....you can do the same with high flow injectors and an extremely hot exhaust....although you will not get the blue colored flame, you still will shoot fire out the tips.
MY Turbo 2.2liter was running 4 32psi injectors computer controlled and 4 32psi injectors pressure regulated to turn on at a pre determined PSI...they were running wide open! when that PSI was met......no electronic regulation.......
NOW my story has been told, your PROBLEM is you re running to FAT(rich) its great to be safe and cool the engine running a hair rich, but you lose drastic power. My question to you is are you running STOCK(as in no A/F modifiers) or do you have an AFC or something of that sort????