Something is reducing my available boost and I couldn't think of anything that would be other than timing. I assumed that if its retarding the timing then thats reducing cylinder pressure and the subsequent pressure to spool turbo? Forgive my lack of knowledge I'm no engineer. 

Timing advance/retard alters the point of ignition (spark) in the compression cycle.  It cannot alter the maximum boost at the inlet manifold set by the wastegate.   
 
Retarded ignition can actually premote earlier spool via higher EGT's, can also provide less/sluggish power, but as above not lower the amount of boost seen at the inlet manifold. 
 
I'd be more inclined to look at the wastegate operation and ebc.  
 
 

Has the tvsv been disabled?

If its a gen II you have tvis which is controlled by you the ecu, if knock is detected it will close the butterfly and you will have only four intake runners open above 3600rpm. After the car has been switch off and restarted it normally reset back to standard if it does not detected it again. This will affect what you feel. Hard corning low fuel in tank can give a lean out, create knock. Just double check for boost leaks etc.

Thanks for the input all. The Phantom boost leak is still eluding me. I've been hammering the car to work all week and not being able to replicate the fault. Really cold mornings the car will have a cough at peak boost but this is likely my EBC just regulating pressure as it wouldn't normally spool up that fast. 
 

feral4mr2
Timing advance/retard alters the point of ignition (spark) in the compression cycle.  It cannot alter the maximum boost at the inlet manifold set by the wastegate.   
I'd be more inclined to look at the wastegate operation and ebc.  

Yea I've spoken with Robk about this as well I was misguided thinking pulling timing would result in boost drop. We're convinced its a boost leak that only happens on some occasions but no idea where to start. I think it's time to just bite the bullet and swap in my CT20b

chausta
Has the tvsv been disabled?

Yes, the turbo is not monitored by the ECU anymore it all go's through the EBC and I have a FCD to stop the boost cut.

grosso
If its a gen II you have tvis which is controlled by you the ecu, if knock is detected it will close the butterfly and you will have only four intake runners open above 3600rpm. After the car has been switch off and restarted it normally reset back to standard if it does not detected it again. This will affect what you feel. Hard corning low fuel in tank can give a lean out, create knock. Just double check for boost leaks etc.

I thought TVIS was only a 4A thing. This could be a potential cause. I've ran diagnostics on the car and it hasn't recorded a knock code but it could be that maybe? Such a frustrating issue. 

Matts_SW20
 
I thought TVIS was only a 4A thing. This could be a potential cause. I've ran diagnostics on the car and it hasn't recorded a knock code but it could be that maybe? Such a frustrating issue. 

Gen 1 & 2 3SG motors featured TVIS. Gen 3 dropped it (Like Gen 3 4AG's)

So if I loose 4 runners would that necessarily decrease boost pressure by turbo? 

You done an intake pressure test?

Matts_SW20
So if I loose 4 runners would that necessarily decrease boost pressure by turbo? 

No.  The turbo and wastegate determine the amount of boost seen at the manifold.  Piping as well given if there's a leak you'll see less at the manifold. 

5SGTE
You done an intake pressure test?

I have not, I'm installing a CT20b this weekend. If the problem persists I'll be looking into this. 

feral4mr2

Matts_SW20
So if I loose 4 runners would that necessarily decrease boost pressure by turbo? 

No.  The turbo and wastegate determine the amount of boost seen at the manifold.  Piping as well given if there's a leak you'll see less at the manifold. 

Yea I thought so. I'll change the turbo and see if I still have this phantom boost leak