Blow-off valves are design for one
thing: to prevent damaging compressor surge to the turbo. By venting
excessive boost due to an abrupt throttle closure (i.e. shifting at WOT),
this prevents all that boost from
backing up into the compressor section of the turbo. If it wasn't for the
BOV, that boost would hit the
compressor wheel and cause damage to the thrust plate on the turbo. Most
people can associate the whistling or whooshing sound of the BOV, but that's not
it's primary function. This is also a tall-tale sound that your car is
equipped with a BOV (and probably a pretty potent turbo or serious boost).
There are a lot of BOV kits available to the FC. Most of the major Japanese
aftermarket tuners offer their BOV's and kits. This includes Trust/GReddy,
HKS, and A'PEXi. These manufacturers also offer their universal BOV's with
no adapter pipes for custom installations. These universal BOV's with the
appropriate mount flanges are designed for custom installs, especially with cars
with long, exposed intercooler pipes.
The stock BOV (or CBV as Mazda calls
it) is only
efficient with the stock boost levels. If you're running a larger turbo or
more than 10 psi of boost, we recommend to go with a larger (aftermarket) BOV to
prevent damage from compressor surge.
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