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I have a question about tuning turbo engines.
When you raise the boost pressure to increase horse power on a turbo engine, How would you determine the amount of boost pressure that an engine can safely take?
That is very much a 'how long is a piece of string' type of question.
Or 'suck it and see' - meaning try it and see when it breaks.
Engines aren't designed to hold a certain boost pressure per se. They will be designed to withstand certain cylinder pressures, temperatures and reciprocating forces.
There will be other limiting factors which affect the maximum boost pressure you can run including the compressor efficiency map of the turbo, the static compression ratio of the engine and the fuel you run. Sometimes 'less is more'.
Remember also that engines respond to mass flow (in and out), not just to inlet pressure!
When increasing boost pressures (and thus cylinder pressures) it's common to upgrade internal components such as pistons and con-rods for stronger items. Bolts, head studs and gaskets are also commonly upgraded to give the engine a fighting chance of staying together, prevent heads lifting etc.
Short of extensive FEA, trial and error or just 'gut feel' there is no real definitive way to know the "safe maximum boost pressure" for a given engine.
If it's a bone stock engine then try asking other owners what they have successfully gotten away with.
As Chris has mentioned, this is a very difficult question to answer as there is so much to consider. The dyno will generally guide you as to the point where your turbo stops being efficient and you stop seeing the power increase as you raise the boost, however that doesn't mean that the engine can handle that amount of power. For stock engines and turbos you're best to spend some time trawling enthusiast forums to find out what others are doing.