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exhaust open after 1st cat.. good or bad?

This is a discussion on exhaust open after 1st cat.. good or bad? within the External Engine forums, part of the LSx Technical Help Section category; i picked up an 04 gto an it had the exhuast un bolted after the h pipe. still has the ...

  1. #1
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    Impulse Blue Metallic
    2004 GTO

    exhaust open after 1st cat.. good or bad?

    i picked up an 04 gto an it had the exhuast un bolted after the h pipe. still has the 4 cats ... just wondering if leaving it that way is bad.. or if cutting the smaller cats off is even worse. thanks guys

  2. #2
    Senior Member Naaman's Avatar
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    Cayanne
    98 Z28 Vert M6

    What are your goals? Are you in a CARB jurisdiction?

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    Senior Member Too Fast's Avatar
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    It won't hurt the car to drive it like that. It's unbolted just after the cats?

  4. #4
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    Impulse Blue Metallic
    2004 GTO

    Yeah unbolted from the cats back... what if I cut off the 2nd smaller cats... is that bad? I want a louder idle

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    Then buy headers. You risk burning up a valve it cold air hits one. Don't ruin a new car like that

    Sent from my DROID BIONIC using Tapatalk 2

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    Senior Member Too Fast's Avatar
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    You won't burn/bend a valve with some exhaust on it. These cars have 4 converters? If the OP does cut off the back 2 converters, and then drives around like that, that won't hurt the engine. The front converters are still plenty hot. Also, to do damage to a valve like that, you'd have to really be having fun with the car. Now if it were like the old days when log manifolds were used, and no exhaust beyond those ancient things, it would be possible, tho not likely to do damage to a valve.

    But like you say, Dave, get some LT headers, eliminate the cats, don't even put any mufflers on it but do a full exhaust, and that would be loud as hell, at idle and otherwise.

  7. #7
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    Impulse Blue Metallic
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    1 3/4. Or 1 7/8?

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    Senior Member Too Fast's Avatar
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    Lots of opinions on that. For huge HP, you'd go with 1 7/8. Go for a quality header tho. Also, if you have no other power adders, then either will be fine.

  9. #9
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    I always go for 1 7/8"

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