Personally it maybe a little of both.
Whats your fuel pressure, is the regulator working (don't assume) find out.
And a 1.6ltr with a t25 id say you wouldn't see anymore then 150-170 anyways, but should be all the way too at least 7200. What psi is it set at. 7,8,9,10,11,12??
Perhaps that 162kw figure was never right.
Rev limited because it doesnt make anymore power tells me something. You have a restriction somewhere. Id say the 3" dump too 2.5" isnt helping.