Google mechanic, I’ve been building performance engines and dyno tuning for 20 years. It’s not what google tells me it’s what physics tells everyone, those pipes have essentially no flow after the valve closes and what does physics say about that? The slow gas velocity is under a higher pressure, about 14.7psi of back pressure. Back pressure impedes flow and can even push exhaust gas back into the combustion chamber as well as the fresh intake out into the air cleaner. Read a book https://www.amazon.com.au/Scientific-Exhaust-Systems-Engineering-Performance/dp/0837603099/ref=asc_df_0837603099/?tag=googleshopmob-22&linkCode=df0&hvadid=341743770390&hvpos=&hvnetw=g&hvrand=7050728797150919472&hvpone=&...
No, an airbox is still useful. The reason is not ram air, which really is a negligible effect until you get to quite high speeds, but rather the Helmholtz effect. If you read about intake design and optimization, the Helmholtz resonance effect can be exploited to increase the amount of air relative to the RPM of the engine. Since we now have a compressor in front of the intake manifold, the resonance becomes a multiple of compressor speed and pulsing.
The compressor still faces backpressure from the intake manifold which will cause it pulse similarly to an NA engine's backpressure (or rather decrease in negative pressure, less negative) in the intake.
Here's a good read:
https://www.amazon.com/Scientific-Exhaust-Systems-Engineering-Performance/dp/0837603099/
Here's a good place to start :) https://smile.amazon.com/Scientific-Exhaust-Systems-Engineering-Performance/dp/0837603099?sa-no-redirect=1
https://www.amazon.com/Scientific-Exhaust-Systems-Engineering-Performance/dp/0837603099 This would be a good start
The whole “lack of back pressure” thing is a myth, all that is happening is the reversion wave arrives at the port earlier and the flow is reduced, this increases the pressure in the pipe and will reduce the amount of exhaust gas evacuated which in turn will reduce the amount of fresh charge coming in, in some cases it will push exhaust gas back into the cylinder and push the intake backwards at the start of the stroke. What is beneficial to performance is having the low pressure in the exhaust which is achieved by high gas velocity, this is more commonly known as scavenge.
Since I always get down voted on this subject, I’ll add a couple of links to help. https://www.omicsonline.org/open-access/analysis-of-exhaust-manifold-using-computational-fluid-dynamics-fmoa-1000129.php?aid=77193
https://www.rbracing-rsr.com/exhausttech.htm
https://www.amazon.com/Scientific-Exhaust-Systems-Engineering-Performance/dp/0837603099 This book is a great read, there is some very deep analysis of exhaust pressure and uses test bed engines in proving that exhausts with higher pressure (Back pressure) results in lower power and less economy.