the tiny turbo on the 1.8T is almost out of its depth anyway mate but honestly the guys are spot on, the only way is a remap. I t doesn't need repeated by me to make it true, but thousands ask the same q and I always felt my 1.8T was strained as standard and pushing it would lead to failure.
they most certainly are not bulletproof like some sellers would have you believe. worth considering that on a standard engine the compression ratio may be say, 12:1 - so with no turbo boost it will compress atmospheric air (14.4 psi absolute) to 12 x 14.4 ie = 172 psi peak cylinder pressure, so then add some boost to +14.4 psi (+1 bar) from a turbo, now you have 12 x 28.8 psi = 345.6 psi P.C.P.
Now, up the boost to 20psi, just 6psi more, and you get 12 x 34.4 = 412.8 psi - an increase of 72 psi at the piston crown....so any boost increase at the intake is multiplied by the comp ratio resulting in a large increase in peak cylinder pressures.
as well as the increased stress on the internals it requires more fuel to go with the increased air so stoich burn ratio can be maintained (even more fuel may actually be needed on top to act as a charge coolant) since if it runs lean at high pressure it can melt through piston crowns quickly during a caning as peak pressures are huge, temps are high, and the only way to increase fuelling is to reprogram the ecu.
boost and fuelling must go hand in hand or bad things happen bud