I am curently boosting 18psi(diode) but the boost seems to just fall to 10psi as the rpms rise. Is there any way to prevent this. I have the mbc inline with the n75. I tryed the mbc alone but had the same problem. I've searched for days but can't seem to find a straight answer.

 

You're running a K03. Nothing more needs said.

 

Have you checked your DV?

 

x2. that little bugger just runs out of breath around 5k. It simply cannot keep up. It's a trooper tho.

 

Yep. It's not just about boost, it's about volume of air to keep the boost up. And that little hair dryer can't do it.
That was the coolest thing about getting a bigger turbo. I had to change how I drove for the powerband, because when the K03 gave up, the GT28RS is still screaming for more.
You can do a boost check. Go to a4mods.com and see the way to do it. It is possible you have a hairline crack in a hose somewhere that only lets loose under the higher boost. It will gradually get bigger over time until you're at the point where you don't even spike to 18psi.
But my guess still, from experience, is that the K03 just falls short at 5k rpm and is done after that.

 

Just physics. The small K03 can only spin so fast. The boost falls off once the acceleration rate of the turbo starts to decrease so does the boost, even though the amount of air being moved keeps rising.


The more boost you try to run on the K03 the sooner you hit that point of where the boost starts to drop. This has an effect on how soon you hit your peak tq and peak hp.