2jz haltech cant rev past 8500rpm

Hello, I am facing problem with two cars which is I can not rev past 8500 rpm, it feels like the engine is stopping, there is no ( limiting function active during this). one of the cars is at 50 psi when this happened and the other car is at 23 psi. Both of them have smart coil ign1a, stock cam/ crank sensor and aftermarket camshaft ( GSC ).

Anyone faced this before ?

Is it a dead cut, or is it struggling for the last few rpm? Do you have fuel pressure? What spark plug gap? What engine management? What is the dwell? What turbo' and turbine housing are you using - it may be developing too much exhaust pressure in the manifold? Etc.

There are many possible causes, but something often overlooked are valve springs, especially seat pressure (force). This is worsened if the valve seats have been machined and they weren't correctly shimmed.

it feels like the RPM is stopping at stays at 8500 or 8400 no more and the power did not drop, 5.5 dwell. One of the cars has 8891 turbo ( made 1500 HP at 8500 50 psi) and the other car 83mm turbo ( made 690 hp at 8500 23psi). both cars has dual valve springs from Ferrea (KT4024) 115lbs with Ti retainers.