The age old creep from the 16G
good at it arent they..
my mate, 87VR4,had boost creep in excess of 20-23 pound when aiming only for 16 pound on his VR4....what we put it down to was that he had made the 16G so efficient that it was outflowing itself (generating more turbine gas than the wastegate could opose or flow away)
Factors that increase the turbine efficiency but help it boost creep
include.
-A very good unrestrictive inlet pipe.
-A Tubular good flowing stainless manifold,or bigger aftermarket manifold
-A 3inch dump/exhaust.
Combine these with the fact that the 16G wastegate channel at the turbine entry is too small and the wastegate flap itself is too small and you have a near uncontrollable problem.
Now if you want to get rid of it..
Like you said about the wastegate port,port it out,port the seat for the wastegate flap,there is enough room there to take some out,but of course dont go too big cos it wont seal,i do beleive you can port it out and use a bigger flap,but i havent seen it done,i have heard of it being done though,and the size 26mm rings a bell somewhere along the line,cant remeber if thats stock size or the size they upgraded to.as you can see by the pic below,you can port that seat away entirely or it wont seal,at best i guess you can only open it up a few mm
Also..the dump pipe wastegate pipe..
This is gonna suck cos i remeber you posted a pic of your dump pipe which means youve already got one yeah??
But a 50mm wastegate pipe that is seperated and enters at around 300mm on the inside radius of the exhaust front/dump pipe (if possible) will be the next best thing to help eliminate it.
also port the wastegate exit chamber on the back of the turbo,(the oval shaped chaber in the pic below) polish it all when your finished with a scotchbrite wheel,every bit of extra wastegate flow helps.
you may have already seen this,but if not here it is anyway
http://www.vfaq.com/mods/porting-turbo.html
good luck.
