Oh, i've read from another member who has DT-S exhaust + ARK HFC's and he said it sounded perfect. I dont know, i've never heard the two combo in person.
As to responding to your questions, i took it to a shop to get them installed. BUT i dont think it does matter UP or DOWN from the looks, however i could be wrong.
I never had my car dyno'd before or after, so i honestly dont know. I let my brother drive and he said he feels a different, but honestly its nothing major increase in power. I have not got my car tuned yet.
Good luck!
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