Boost control with no waste-gate

Hey guys! A friend of mine recently turbocharged his car which has an economy, low power, naturally aspirated engine. He made the coversion with parts he had hanging around in his workshop including the turbo itself which couriously has no wastegate built into it, to solve the inconvenience he intalled a pop off valve that ventilates when the desired boost pressure is needed.

He reached to me asking for advise. Eventhough the system works correctly my worry is that constatly spinning at maximum speed must be harmful for the turbo itself but I would like to know what you guys think.

Did he install a pressure relief valve on the compressor outlet side or an external wastegate on the exhaust side?

sorry for the inaccuracy, he installed a relief valve right before the throttle in the intercooler piping

In the early days of turbocharging they did not use wastegates (especially on diesels). They just relied on sizing the turbocharger and the rest of the system to keep the boost down.

He could be overspeeding the turbo but if he has a restrictive enough exhaust it may not overspeed. One concern is that the backpressure will increase the chance of knock. In my opinion he could get away with it, but it is going to reduce performance.