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Expected HP gains from cat delete or replacement?

Posted by BLACK'98DSM, Sep 19, 2019

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  1. BLACK'98DSM

    BLACK'98DSM Proven Member

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    My cat is heavy and ugly, also very restricitve. Gonna delete or replace with a Magnaflow Performance one. How much hp can I expect to gain? Or any?
     

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  2. Ludachris

    Ludachris Founder & Zookeeper

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    Depends on how restrictive the rest of the exhaust system is. If it's really clogged and is neck-down in the system you'll feel a nice gain. I remember when I removed my high flow cat and put on a straight pipe it was a noticeable difference using the butt dyno. Unfortunately, when I replaced the cat on my both the 1g and 2g I also replaced the stock exhaust with a full catback, along with a high flow cat and downpipe, so I can't say how much difference just swapping out the cat would be on its own.
     

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  3. BLACK'98DSM

    BLACK'98DSM Proven Member

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    Already have headers and downpipe, and also a muffler. So basically the cat is the last aspect I need to remove or change.
     

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  4. Ludachris

    Ludachris Founder & Zookeeper

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    Is it a stock cat? If it is, does that mean the downpipe and catback both reduce down to the size of the cat? If so, removing those transitions and making it one continuous size will also help.
     

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  5. BLACK'98DSM

    BLACK'98DSM Proven Member

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    Yes, it's the cat that came on the car 22 years ago. I'm thinking of cutting the cat off then welding a piece of straight pipe in it's place. This pipe will be the same size as the rest.
     

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  6. Ludachris

    Ludachris Founder & Zookeeper

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    Yeah, if the downpipe and catback have the smaller piping and flanges, you'll have to chop those off and replace the flanges and short runs of pipe to make it the same size as the rest of the exhaust. I had to do that as well.
     

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  7. 609DSM

    609DSM Proven Member

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    Just bang out the core with a sturdy pipe, if you don't have emissions testing in your state. Not recommended though cause it's kind of a grey area.
     

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  8. ec17pse

    ec17pse Freelancer

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    Its not really power made its how it feels in acceleration as it will flow better. It will gain something but your likely feel more from throttle response etc as its not as restrictive as once before.
     

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  9. silvreclips

    silvreclips Proven Member

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    On a non turbo car I would not remove the cat. You could use a high flow cat but I wouldn't remove it completely.
     

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  10. rabenne

    rabenne Proven Member

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    I cant really speak intelligently on quantifiable gains, so this is entirely anecdotal, but with my exhaust dump closed I am forcing everything thru a fully baffled muffler and with it open it is 3" from o2 housing straight back. (Varex muffler w/ built in flow control valve VMK11-300)

    When I do a pull with the exhaust closed there is noticeably different (later) spool characteristics and power delivery feels reduced and shifted right (later in RPM band). For that reason I would say your gains will be noticeable. @silvreclips suggests not removing the cat on an NA car. Hopefully he will elaborate on why he feels that way. I am pretty curious... Otherwise - welding in a straight pipe of equal diameter (as you mentioned) is a great option. But let's wait to see what silvr says because I could be overlooking something.
     

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  11. BLACK'98DSM

    BLACK'98DSM Proven Member

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    It's the cheapest and best flowing option. Why is that so?
     

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  12. Ludachris

    Ludachris Founder & Zookeeper

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    Oh hell, didn't even notice this is for a N/T car... Not sure you'll notice too much outside of better response, maybe a little more pep. If you dyno'd the car it might be a few HP.
     

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  13. silvreclips

    silvreclips Proven Member

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    It really depends on what your goal is with this car. If you remove the cat you will most likely get a small HP gain in the high rpms. However, removing the cat will hurt the low/mid-range power band. You will hear people talk about exhaust back pressure, but what really is happening is you will lose the exhaust scavenging that helps remove the burned gases from the cylinder. Do some research and you can see what I'm talking about.

    On a turbo car it's a different story. You want to get rid of as much exhaust as quickly as you can.
     

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  14. BLACK'98DSM

    BLACK'98DSM Proven Member

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    Sounds like a high flow cat is the way to go then.
     

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