Loss of Boost about 4500 rpms

[PCONE90GSX]

I am running a 14b turbo, I just got a ported 2g manfold put on and a boostleak test done, no boost leaks. Now I have my boost controller set at 15psi. It holds steady at 15psi until 4500 rpms then the boost immediately goes back to 11. Its very weird because the engine held boost great before I got my exhaust manifold ported and replaced with a bran new 2g one. If anyone knows what could be the problem please let me know, thanks.

 

[TheCrazyDSM'r]

I would look again for leaks and maybe look for a bad vacume line.

 

[PCONE90GSX]

yeah just did that, no leaks

 

[LessIsMore]

Check for exhaust leaks. A loss in exhaust gases would cause a drop in boost. If all you've replaced since the car held boost fine is the exhaust manifold then I would assume it has something to do with that. Did any exhasut manifold studs break? Did you use the metal, two ply manifold gasket? Have any of your exhaust manifold to turbo bolts backed out? Just a few things to check.

 

[PCONE90GSX]

everything looks great with the exhaust manifold, nice and tight, and the two ply gasket was used