Probably a stupid question. I hear people say that open wastegates are loud, but is it loud all the time, or only when the wastegate is bypassing the exhaust around the turbine and to the atmosphere?

 

It's only loud when dumbing exhaust air to the atmoshpere. Sounds like a sport bike, kinda cool if you like noise.

 

The dump on my street ported motor thru an HKS race wg was so loud it nearly split my eardrum the first time it dumped. This was with a short dump pipe pointed down and back. I recently worked on another car with a non-ported motor and a wg dump, to my surpise I could barely hear the dump when the wg opened.

 

^ what he said ...

no rule of thumb, it depends on overall setup.

 

When the cops pull you over, that's for sure!

 

The wastegate valve will open when the turbo reaches it preset amount of boost. Most usually, they are very loud. Especially when they are mounted pre-turbo, on the manifold. If you drive around and keep the boost below the preset level and less than 60% throttle (or so), the wastegate will never open, and you wouldnt have to worry about noise, or cops. I can drive my car building up to 15 psi and never open the wastegate at all. But if I go WOT, it's loud as hell.

Also, something to note. As far as loudness of noise; it might make a difference what size WG you are using. Obviously, a 38mm will have to open farther and/or longer than a 44mm gate, and that alone might have an affect on the noise level.