R33 Gtr Not Holding Boost (standard) After Exhaust Install?

[GD51LA]

threw her on the dyno today the power reading was a low 162AWkw. all standard except for front pipes hiflow cat and 3.5 cat back. and what ever boost increase the exhaust gives. i belive it should be around 170-180 at the wheels

the tuner said the boost level was ok, then why is it making no power? i did a comprsion test and all cylinders were dead on 175

my tuner said it could be the plugs or coil packs, what symtons does a poor coil pack/plugs give? definately not 10 or 20 kw..

my boost reading on the standard tacho is still below standard, i dont belive its a faulty tacho for two reasons..

# the car is twelve years old and ive owened it for two mounths..that failure is qite a coincedence dont you think??

# the time i felt the car loose its power was the same time my boost needle was reading less boost.. qite a coincedence dont you think??

what else could be doing this to my beast??