Blow of valves
'Blow off valves' which vent to atmosphere result in the engine receiving a different amount of air as that measured by the air flow meter. As a result the engine will run very rich when the BOV operates. Do not use blow off valves. Internally recirculating valves like the stock recirculation valve are acceptable to use.
Turbocharger over-speed
A turbo relies on intake manifold pressure to limit its speed. If the turbocharger discharge is unrestricted, then the turbocharger will reach an over-speed condition. At high rpm this is likely to destroy the turbocharger and therefore the engine.
The most common cause of turbo over speed is a boost pressure loss from a split or disconnected hose, or leaking intercooler pipes.
Vehicles with a small turbocharger relative to the size of the engine (2018+ 2.0T Accord) can reach a turbocharger over-speed condition with no boost leaks.
Turbocharger in overspeed condition
The symptoms of turbo over-speed - boost pressure not reaching the boost pressure target and also the wastegate being closed (near 0 mm). Note that during spool up these conditions exists, but not at high rpm.
Turbocharger in normal operation
Normal turbo charger operation - the boost pressure matches the target and the wastegate progressively opens to limit boost pressure.