Could EXH/Man be reason for boost drop?

[grepin]

Further to a post I had on here before I am still having boost drop problems at high revs. I am wondering as I have a custom exh manifold wether it could be an issue. Has anyone else had problems with custom manifolds?

I have as sujested before put a 20psi spring wastegate (internal) actautor on and the boost always drops to 15psi (regardless of trying to run 19 or 17psi achieved at 5000rpm then dropping)

The turbo is a 2835ProS 0.64 Exh A/R and 56Trim 0.5 A/R Comp 420ps. Have a largish internal wategate of 40mm.

It may be running out of puff.

40psi has been measured in the turbine housing.

Boost is doing exactly the same at the plenum as at the Comp housing across large intercooler and greddy plenum so no leaks.

Visually I can see the wastegate starting to open before max revs have reached.

I have a good flowing 3.5inch dump fitted. I am wondering as a test wether I should bolt on a standard exh manifold to see if it helps. Idealy I would like to be able to hold 18psi right across the rev range. Various boost controllers have been tried all do the same.

I am making around the 285rwkw dropping to 15psi boost which I am happy with however its anoying knowing I cant hold boost.

[Ustasa]

Dude 420hp at crank is around 310kw. Lose 15% to rear wheels and there you have your 285rwkw.

Turbo is out of puff.

Time to get a GT35R on and some 272's (with springs)