My alu pipe is self-made or, more exactly self-concepted because I've not the abylity of factoring alu pipes ! ;-))))
You must first keep in mind that it's generally admitted that 5°c minder(admission air temperature) gives you 1 powerhorse more.
But it's difficult to win 5°c and temperature is not all, volume, airflowspeed, ..... are other important parameters.
In my case, the alu pipe is 10 mm larger than original pipe to create a small air reserve (improving throthle response) without having a dramatical airflow speed decrease.
Helping this speed, internal faces are also polished.
The silver colour of the pipe protects the air inside the pipe from the motor heat (thermo effect) and I've mesured a 5-6 °c difference with the original pipe(combined with tha Autodelta carbon air intake).....but that was not the goal.
Carbon is also a goot heat insulator but the black color is working again himself, especially just near a heat source.
Internal face of a carbon tube is also generally rough and that's not good for the air speed in the tube; So I thing that you should use carbon only far away from any heat source and only before the air filter.......just like autodelta do !
You'll say me that the race 147 use big carbon air boxes just near the motor and you'll be right but in this case, inside faces are polished too and carbon has been choosen for his rigidity. Air pressure in those boxes is high (for creating a mini turbo effect) and its important not to loose this pressure in material flexibility and, perhaps the most important, these motors don't have MAF so, available air volume MUST be as regular as possible.
I'm writing a technical article about air admission and it will be soon available on my site.....I hope.