F1technical.net

It would seem that a turbocharged engine would not be able to, nor has much of a need to for, pressure wave tuning of the exhaust system. As to the first concern, the turbine would pretty much disperse the pressure wave. And with the ability to enhance volumetric efficiency to the point of detonation, pressure wave tuning would be redundant.

Is this valid?

You still get the pressure wave effects, but the boost from the turbo will utterly overwhelm it.
A lot of people more experienced that me with turbo engines keep telling me to not worry about primary pipe length too much, just keep the system as short as you can to keep the heat (energy) in it before the turbo.

Normally you want a diffusor in the exhaust after the turbine in order to reduce the pressure p4 after the turbo. This gives better efiicency.