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Old 10-16-2006, 06:20 PM   #1
Scooby Newbie
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2006 Subaru STI WRB
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Default true or false about catalytic converters

true or false

They make your car sound quieter.

Is is true that your car will sound even louder without catalytic converters? How much louder if so?
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Old 10-16-2006, 06:34 PM   #2
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11 STI sedan


True. The cat will muffle the sound of your engine just like a resonator. How much louder depends on the size, material and shape of piping in the rest of your exhaust system.
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Old 10-16-2006, 06:38 PM   #3
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2006 M5


On my Evo, I have a resonated test pipe that is quieter then my high flow cat with metal substrate. I was amazed that it would be like that...
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Old 10-16-2006, 06:58 PM   #4
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2008 Mitsu Lancer
Apex Silver


Stock cat does keep your car quieter, yes. HFCs are more of a crapshoot depending on design.
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Old 10-16-2006, 07:25 PM   #5
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They're supposed to, but I replaced both my cats with a bellmouth downpipe and barely gained any volume at all. It's BARELY louder than stock and that's at idle.
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Old 10-16-2006, 07:51 PM   #6
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05 LGT


They make your car quieter but it is not their only purpose.
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Old 10-16-2006, 07:59 PM   #7
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exhaust flow restriction typically results in muffling.
obviously not the case with "mufflers" designed to get noticed. Design plays a large role in amount of muffling.
Think of a paper towel role as an exhaust and you talking through it as the engine noise,
more restriction=less noise. However design plays a role like cheerleader megaphone cones, or kazoos, or ... you get the point.
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Old 10-16-2006, 08:07 PM   #8
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They say they will make them quieter, but my dB testing does not bear this theory out.

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