At risk of getting flamed...
If you want the best gain, avoid metals for the piping, or coat the metal. Metals hold heat more and cool more slowly, plastic actually stays closer to ambient temps and should generate equivalent velocity in the same size and shape/length. Have you ever noticed this on K&Ns site;
" there are two K&N Air Intakes to choose from. The 57-1529 gains 8.63 more HP @ 4688 RPM with a black non-metallic tube and the 77-1529KP has a 6.8 HP gain @ 4743 RPM with a polished aluminum tube."
I like to make fun of PVC intake pipes, but the principal is actually superior... Just remember its all about INSIDE diam.
If you do a pvc intake, scuff it good and paint it. If it has the size and the word PVC on it I will make fun of you...its a habit I cant seem to break.
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