300ZX variable valve timing broken?

I think your running test pipes and switched back to cats to legalize. Now lets get down to it. What timing are you running 15 degrees 20 or premium fuel only 25 degrees ? miles on that car manual trans most likely or you would not feel the 3200 rpm power rise. Fuel filter last changed? Get out a timing light and see if the timing is retarded (timing belt jumped a tooth) Hopefully you do that every 4 years. If the front end alignment is toe out or in that can cause the tires to scrub of speed too? A little rattle on start up is not abnormal till oil pressure comes up. Good Luck