Head gasket went last month, DAMN !!!

But the engine is getting and using all the air it needs for the amount of power you are asking from it. You are in control of that power.
The only way this Gee Gaa might make 'More air' is if you are 'foot to the floor' on a mountain climb.
Then maybe you could see the difference between identical Prii with this thing installed, but doubt it.
But then don't get me started on how well a K&N filters the air.
When you can hold it up to the sun and see dots of light shining thru.....

As for the sound... I'm so tired of that 'Rubber Band' sound the Prius engine makes, in stock form.
But I came from an EV.
I can't imagine more intake roar....

In fact, I say the stock Gen3 Prius is a brutally noisy car, and I have my tinnitus ringing now after a long road trip, to prove it. I bought ear plugs for the return trip and that was nice!

But thanks for pointing out this service!
I'll be probably needing it someday, because,,, you know.
I can keep my EGR system clean, keep the engine coolant fresh and yet...... How long before this problem shows up?