Boost Drop after 4000rpm

Hey guys, on my CA18DET, pretty standard, i have noticed on my boost gauge that the boost drops over 4000rpm, so i was wondering is this because the CA18DET only makes power with T25 from about 2500rpm - 4000rpm, my boost cut is disconnected and my waste gate actuator is connected directly to the turbo's compressor housing nipple, im not really concerned as the car has always done this and i know T25 doesnt make power over 4000rpm, i was just wondering is this normal and would a boost controller improve boost drop in the higher rpm's. My boost peaks at 0.7 and then slowly drops to about 0.4/0.5. And yip im sure theres no boost leaks. Soon il be upgrading to T28 anyways.

What are your guys take on the matter?

It is not normal to fall directly over 4000, around 5500-6000 thats normal to fall with 0.2, if yours fall directly after 4000 I'd say your actuator spring can not hendle the pressure anymore or you have a crack in your turbo echaust housing where the wastegate seals.

Thats assuming you are right by saying you are sure there is no boost leak....

Hey draco, I must have a closer look, don't think it drops right after 4000rpm, think it takes a while, I can't really watch the boost gauge and rev counter and road at the same time in detail lol, but shot for the input, I'm quite sure there's no cracks, and no boost leaks either, car still performs well, just an observation I wanted to pick some brains about, I hear T28 gives power till 5500? That will be good

T28 doesn't really drop off.

The T28 should hold it's boost all the way to the red line, thats also assuming everything works the way it should.

Also remember there is a few different versions of a T28 but I am sure you have the common one from the Europe SR, heads up though, these T28's have a tendancy to have a weak actuator spring, you struggle to set it right, it's either 0.4-0.5 or it jumps to 0.8-1bar, you really struggle to get it inbetween, if you get it there, next time it's totally off again, so look at that before you install it.

Shot for the heads up Draco, i will definately have a look at that then, i have yet to buy a T28 though, What do you suggest about the actuator then? fit an aftermarket performance actuator? howmuch do they go for, and is it almost a universal thing?

The after market one will be the best, you might need to make it fot though, I suggest you try turbo direct when you have the turbo and ask them for the right actuator, think thats the best bet.