How much boost the engine will take is more an issue of fuel supply. The engine itself should take as much as the CT-26 is capable of while still in it's range of efficiency. Running lean, a bad head gasket, high engine temps and carbon buildup are the largest concerns when just pushing the CT-26.
The CT-26 is efficient up to between 12 and 14psi, after that the air it's pushing out is hot to the point that you're more likely to lose power due to the ECU pulling ignition advance.
The OEM bypass valve will handle 14 or so psi but naturally that depends on what shape it is currently in. If it needs replaced I would go with a Bosch, they're inexpensive and plumb right in. I do not recommend going with an atmosphere vented BOV if you don't have the ability to tune for it (which you don't).
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