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Discussion Starter #1
I just put my catless downpipes (Kooks) on and I have 1 major gripe I hope there is a easy solution to. Between 3-4k RPM with the motor under load, there is a REALLY loud raspy sound (think straight piped Honda). At WOT it continues into higher revs but not as loud. I have the factory sport exhaust so this basically is straight piped now. My gut says put resonators in but I don't know that there is a good place to put resonators with the stock exhaust. Ideas that don't include buying some several thousand dollar aftermarket exhaust?
 

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Get rid of the heat shields. Stock down pipes require heat shields because the OEM cats retain a lot of heat. When you go catless you don't need the put the factory heat shields on, since there in nothing in the pipes to retain the heat. You can leave as it or use header wrap.
 

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The noise sounds way louder in the car, but this is it
I'm wondering if it might be the heat shield vibrating on the pipe as it moves while on the throttle. I'm going to take the panel off again (sigh) and see if there is any evidence of contact.
I have some Fabspeed catless pipes coming to me Tuesday 1/7. They will be installed with my sport exhaust so I am curious what they will sound like. I will post a video for comparison. In your case I don't think it is the heat shield vibrating.
 

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Discussion Starter #6
Get rid of the heat shields. Stock down pipes require heat shields because the OEM cats retain a lot of heat. When you go catless you don't need the put the factory heat shields on, since there in nothing in the pipes to retain the heat. You can leave as it or use header wrap.
The heat shields I speak of are the ones above and below the factory exhaust, NOT around the downpipes. I have Kooks, they're coated so it doesn't even have mounts for heat shields.
 

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Get rid of the heat shields. Stock down pipes require heat shields because the OEM cats retain a lot of heat. When you go catless you don't need the put the factory heat shields on, since there in nothing in the pipes to retain the heat. You can leave as it or use header wrap.
Thanks for the info. I am putting a set on next week and planned on putting the shields back. I will ditch them. My catless pipes come with their own wrap also.
 

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Discussion Starter #8
I haven't taken the panel back off yet, but in feeling around it I feel the noise has to be coming from the exhaust itself. It's a resonance that's happening in the pipe, though I don't know which portion. Unless someone has another idea, I might exhaust wrap or insulation wrap the factory portion to dampen the resonance in the pipe.
 

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Discussion Starter #9
Well, if you know me you know I'm impatient and I don't take no for an answer. I got to digging and I found a lot of people in various cars mentioning catless rasp, and often times it only did it when cold. After exhaust temperatures got up, it wasn't as loud. I observed this myself and thought I was fooling myself. So, where do we go from here? At 9:30 at night when everyplace is closed, I go out to my garage and tear it apart again, use all of the header wrap I had on hand and get to it.

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The idea here being it will still have the rasp at first, but the wrap will keep the temperature of the exhaust higher and scavenge better, making it quieter or inexistent. Maybe it will do nothing, but it cost me an hours worth of time and $0 to find out. If it does work, we learned something.
 

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Discussion Starter #11
Try to remove the H section and make it a straight pipe system if you are good a fabricating. Tat should get rid of any resonance.

What are you all paying of down pipes these day?
I feel like eliminating the H section would make it sound like 2 straight piped 4 cylinders. My friends Mercialago was like that when he got it, sounded like two 350z's having a rev battle.

I didn't pay anything for the downpipes I got, I definitely wouldn't have paid their asking price for them if I was.
 

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Does the rasp come from being catless? Do you think sport cats (200-300 CEL) would be much better?
 

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Discussion Starter #13
Does the rasp come from being catless? Do you think sport cats (200-300 CEL) would be much better?
Yes, being catless is the cause. A high flow cat would prevent the rasp. However, I did a test drive the best I could do in torrential rain and discovered the exhaust temperature matters with the rasp. Wrapping the exhaust did nothing for the rasp, but it will make it hotter and quicker. After some driving in 48 degrees and pouring rain, the rasp went away. I suspect there will be less effects in summer. At least I know it's a short term annoyance at the very least.
 

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Yes, being catless is the cause. A high flow cat would prevent the rasp. However, I did a test drive the best I could do in torrential rain and discovered the exhaust temperature matters with the rasp. Wrapping the exhaust did nothing for the rasp, but it will make it hotter and quicker. After some driving in 48 degrees and pouring rain, the rasp went away. I suspect there will be less effects in summer. At least I know it's a short term annoyance at the very least.
Ok good to know - Would there be a big difference in rasp or any drone with a 200 CEL vs 300 CEL sport cat? I believe the SOUL downpipes are 200 CEL and Larini are 300 CEL.
 

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Discussion Starter #15
Ok good to know - Would there be a big difference in rasp or any drone with a 200 CEL vs 300 CEL sport cat? I believe the SOUL downpipes are 200 CEL and Larini are 300 CEL.
The fact that there is no drone being catless or with basically any other exhaust makes me think you surely won't with a variation of a cat. The pipes simply aren't long enough to have the resonant frequency that would be considered "drone". I could turn that into an acoustics lesson, but the reason for the rasp is exhaust pulse timing and the density of the air (which is effected by the temperature of the air). Cats change the pressure in the pipe downstream, regulating the pulses some. As for 200 vs 300, there is probably a measureable performance difference (which I suspect will be insignificant) but from a rasp standpoint I'd expect to have none in either case.
 

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Does the rasp come from being catless? Do you think sport cats (200-300 CEL) would be much better?
Yes Sport Cats will certainly help 'take the edge off' and give you a more refined tone over Catless DPs.
 

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From personal experience exhaust components do sound a bit different after some use, probably due to various deposits.
 

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Yes, being catless is the cause. A high flow cat would prevent the rasp. However, I did a test drive the best I could do in torrential rain and discovered the exhaust temperature matters with the rasp. Wrapping the exhaust did nothing for the rasp, but it will make it hotter and quicker. After some driving in 48 degrees and pouring rain, the rasp went away. I suspect there will be less effects in summer. At least I know it's a short term annoyance at the very least.
I have Larini DPs with high flow cats. I get the same rasp, tho likely less extreme than yours. It’s a characteristic of the engine. I have not heard a single 12c that doesn’t do the same thing. Reminds me of a beastly version of an old M3. There are worse things!
 

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Discussion Starter #20
I have Larini DPs with high flow cats. I get the same rasp, tho likely less extreme than yours. It’s a characteristic of the engine. I have not heard a single 12c that doesn’t do the same thing. Reminds me of a beastly version of an old M3. There are worse things!
I've seen several videos of various downpipes and haven't heard the rasp. Maybe it doesn't come through as much on video, as mine was the case.
 
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