MAF housing maxed @ 10psi?

Engine - EJ257 (STi) shortblock
Rebuilt heads by drakes who also did all the machining.
Manley Valves/springs/ retainers
Ferra guides
Manley pistons 8.5:1 Stock bore
Polished crank
ACL main and rod bearings.
OE gasket kit.
XO2 front mount
BNR VF40 TD05-18G turbo.
SPT Short ram
Perrin(I think) inlet hose
Invidia catless up pipe and 3in down pipe.
Gimmick Motorsports 3in stainless cat back.
TGV delete.
Gates T-belt kit
Water pump
08+ STi oil pump

I maxed my MAG housing at 10PSI @ only 270 AWHP

Now, I have a KStech MAF that I haven't installed, but I feel there is something else I am missing.

Boost leak under boost maybe?

What do you mean by "maxed out"? To me it sounds like you need to rescale your MAF voltage, I doubt you've reached the choke flow limit of the actual housing at 270hp.

My $0.02, hope it helps

I presume you mean MAF at the end and not MAG - I searched for MAG housing as a brand... Are you talking about the stock airbox? The stock airbox as many of us still have will flow for a lot more power than 270AWHP - there is indeed something else going on as you suspect. Boost leak under boost, as opposed to any other time? Have you performed a simple boost leak test at all, do you have a boost gauge - did the tuner - was 10psi all you made for boost?

Your MAF should not be seeing boost.

As far as I know, boost is after the turbo.

Where is your MAF sensor ?

My MAF was at max voltage, and seeing I'm only open source I don't have much I can do until I get to speed density.

I was told I needed a bigger MAF housing to get more power, but after last night I found my BPV won't hold more than 8-10 psi. It spikes at 14 and then bleeds down to 8 psi and holds there.
err
So, there is my problem.

indeed.