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I am waiting for a 2013 STI and have been looking into upping the performance, but before I go down that road I would like to thoroughly understand the components in a forced induction vehicle.

I've done a bit of reading but I'm still confused as to the difference between a blow-off valve and a wastegate. These two components seem to do the same job ie. prevent too much boost/pressure from being created. From what I understand, the bov releases air if the psi gets past a certain point and the wastegate prevents exhaust gases from spooling the turbine past a certain pressure. Am I missing something? I'm sure I am... Could someone please clarify for me?

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Possible duplicate: You'll find several questions and answers discussing these components. You might find this question in particular to be informative: mechanics.stackexchange.com/q/2731/57 –  Bob Cross Feb 3 '13 at 21:15
Clarifying the original intent: if you are looking to up the performance of a forced induction vehicle, neither a wastegate or a blow-off valve will help. Neither is a power producer. They're just necessary plumbing. –  Bob Cross Feb 4 '13 at 13:16

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up vote 3 down vote accepted

The waste gate is designed (as you'll see in Bob's excellent answer to his linked question) to avoid spinning the turbo up unless needed. This saves fuel and wear.

The blow off valve or dump valve is designed to stop a compression wave passing back into the turbo when you close the throttle, as this wave could stall the turbo completely, which can put high stress on the turbo, as well as making it take a long time to spin back up again (turbo lag)

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Turbo Esprit models without BOVs are well known for high turbo failures. Adding a BOV is the typical first modification, just to avoid the the need for repeated turbo replacement. :-) –  Brian Knoblauch Feb 4 '13 at 12:56
+1 for flattery ;-) –  Bob Cross Feb 4 '13 at 13:14

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