A true cold air intake can add about 10 HP, but mostly at very high RPMs. Is a 9-10% horsepower increase noticable? Sure, at high RPMs (past 4500 or so).

What you have is a warm air intake - definitely an improvement over the stock unit. Now if you can somehow channel cold air up from underneath, you could gain another 4-5HP over the 5 that you just gained.

 

This is funny because I have a Tenzo R CAI in my car too, only I dont think it was even built for a civic... lol. I bought it from a friend for 5 bucks and had to squeeze it in right behind my headlight, it looks good and sounds really nice though, especially when I shift past 3k rpm.

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