Awesome maths, I agree with your conclusion as far as when the pipes will be "needed", and that there are likely gains that your formulas can't account for by smoother bends, loss of kinks, etc.
To the point of manufacturer dynos showing gains, you are talking about a part similar to the turbo muffler delete, turbo inlet pipe, "upgraded" silicone IC connectors. All of these together will effect something, but any one of them on their own might show zero identifiable/repeatable increases on a dyno. That is the nature of dyno testing, because even same car, same day, same fuel, same dyno can have a few % variation between runs at different parts of the RPM ranges, not just peak numbers. So when your gains could be 5 hp, that's within the variation over say 3 dyno runs and your gains are "lost". Why would you want to advertise that? You wouldn't, so you just don't see dynos.
There may be other more identifiable gains like noise, spool time or throttle response, and that's the merit most of those parts sell on IMO.
To the Stage 3+ 500hp and up club, if this is a bottle neck (which is isn't on up to IS38 cars if maths stick) then you should definitely see a verifiable improvement on a dyno, and it would be good to see a back to back to prove that.
To the point of manufacturer dynos showing gains, you are talking about a part similar to the turbo muffler delete, turbo inlet pipe, "upgraded" silicone IC connectors. All of these together will effect something, but any one of them on their own might show zero identifiable/repeatable increases on a dyno. That is the nature of dyno testing, because even same car, same day, same fuel, same dyno can have a few % variation between runs at different parts of the RPM ranges, not just peak numbers. So when your gains could be 5 hp, that's within the variation over say 3 dyno runs and your gains are "lost". Why would you want to advertise that? You wouldn't, so you just don't see dynos.
There may be other more identifiable gains like noise, spool time or throttle response, and that's the merit most of those parts sell on IMO.
To the Stage 3+ 500hp and up club, if this is a bottle neck (which is isn't on up to IS38 cars if maths stick) then you should definitely see a verifiable improvement on a dyno, and it would be good to see a back to back to prove that.