I think the consideration in cc'ing the tubes is exactly what you were saying about the "effective length" of the primaries?
The guy who was teaching me head porting was telling me that parts of the intake port have little or no effect in increasing the volume of mixture able to flow within a given time period.
He also thought that the short turn radius into the valve pocket was the most important and used the analogy of a water fall as what he thought was happening there.
He thought that if the radius was correct that the mixture would flow like a liquid would at that point so the radius of the turn was very significant to the flow. The flow should be treated as a liquid would at that point.
Certainly harmonics can be heard in the intakes as well.
Exactly what is happening in the exhaust probably has similarities to those thoughts but if the current thought of modeling is that the harmonics are what is being tuned, who am I to argue?
Certainly the harmonics of the GT40's at Daytonna in '65 in the distance is what I noticed on the "bundle of snakes" exhausts they were running.
The Cobras would run by with an entirely different sound. The sound of the GT40 exhaust in the distance was unmistakable.
It was said at the time that the exhausts on the "40's" was thought to be worth about 100hp over the Cobras.
It's also interesting to me that the length of those primaries tuned the 289 to be all in at about 5,500 rpm? They certainly were being turned much higher then that.
I got "yelled at" by a couple of "vintage guys" that still work for Holmon-Moody, that the engines, at least in the case of the 427's, was strictly limited to 7,000 rpm, because of the limit of valve spring technology at the time. This for an engine that every other component seemed to be built for over 8,000 rpm's?
That certainly isn't the problem these days at all.
There weren't many shops back then with chassis dynos and if you think about it what the head porters were doing was copying "models" that they knew improved performance. The terminology hadn't been coined yet then to explain it.
Now everyone who has a software program that works with this can essentially design a profile that can be cut on a CNC machine and maximize for the criteria desired.
I think though that there will still be debate over whether the engine should be tuned for peak hp or maximum hp increase under the curve?
I tend to think for peak hp?