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Discussion Starter #1
Those who know, could you approximate or roughly quantify the increase in noise resulting in the installation of a decat downpipe?

I’ve had one sitting around for ages, afraid it will be ridiculously loud.
If it’s only bloody loud that would be fine. Please choose the word you feel best describes the noise after deleting your cat. Decibels or sound pressure rating mean nothing to me so please be as descriptive as you can without obscenity :)
Would be good to be able to decide quickly because an opportunity to have someone install said decat downpipe has arisen.
 

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Cold start loud AF, you can tell car is modded. Idle sounds good to me, hard to tell the difference between OEM and modded. WOT and shift farts are something to consider driving around the town at night. I'd say a race car level loud. Crusing speed a bit louder, but no major difference.

Power gains? On modded ECU we are talking about 20-30hp of top end power increase, right where the 4C lacks a bit of the kick.

 

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OEM downpipe with integrated CAT is very restrictive. On stock ECU with goal max boost, even if you change downpipe w/ cat, no significant gains will be achieved as turbo has no problems achieving goal boost levels. On tuned ECU, where turbo has to produce the extra boost while fighting backpressure, the free flowing exhaust does miracles.
 

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Discussion Starter #5
Wow, I’m fitting it!! Thanks! I too had no idea it unleashed 30 additional horses!
I have the Alfaworks stage 1 ECU...
That sounds awesome in the video!
 

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Loud isn't the point. The exhaust smell will not be tolerable. I replaced the cat with 400 CEL High Flow cat and the smell isn't a problem and better flow than stock CAT. However, the car is now muted.
 

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Those who know, could you approximate or roughly quantify the increase in noise resulting in the installation of a decat downpipe?

I’ve had one sitting around for ages, afraid it will be ridiculously loud.
If it’s only bloody loud that would be fine. Please choose the word you feel best describes the noise after deleting your cat. Decibels or sound pressure rating mean nothing to me so please be as descriptive as you can without obscenity :)
Would be good to be able to decide quickly because an opportunity to have someone install said decat downpipe has arisen.
Very loud without any muffling. Aggravated my tinnitus to the point of scary which is why I’ve not gone ahead with it. Thanks to alfa1105 for the demonstration. He ended up putting twin hot-dogs on his as I think it got too much, even for him.
 

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Discussion Starter #10
I have the valved, dual mode Quicksilver so I will still have something to moderate it slightly. I’m thinking about running a cat on a valved bypass further downstream so I have even more options.
 

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I have the valved, dual mode Quicksilver so I will still have something to moderate it slightly. I’m thinking about running a cat on a valved bypass further downstream so I have even more options.
Never short of ideas, Floro. (y)
 

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Discussion Starter #12 (Edited)
I’m thinking a cheap restrictive cat is best, as long as you can bypass it for normal use. A restrictive one will yield good emissions for the yearly MOT as well as be a more effective mute button.
111498
111499
 

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I’m thinking a cheap restrictive cat is best, as long as you can bypass it for normal use. A restrictive one will yield good emissions for the yearly MOT as well as be a more effective mute button.
Going to be hard to find room to put a cat / valve and bypass in the stock catalytic converter location. So you'll need to move it downstream where it will take a bit longer to heat up. Will that cause the computers any aggravation, I wonder?
 

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Discussion Starter #14
Yes, downstream as I said ;)
It can’t cause any more trouble to the ECU than no cat at all so what’s the dif?
 

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Yes, downstream as I said ;)
It can’t cause any more trouble to the ECU than no cat at all so what’s the dif?
You want it there to fool the emission testing. Is that a tailpipe "sniffer" test where you are, or do they check for stored codes?
 

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I have no way of uploading the videos of my car because I don't have a computer to put them on here and my phone isn't allowing it. Novetic downpipe makes it sound sooo much better. But I also have the Eurocompulsion phases 2 tune with pops and bangs. Worth every single penny. So much louder, its not rattley, and doesn't sound like a fart can.
 

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Titanium Exhaust
Decat Scara 73 : 119 dB View attachment 111504
Just to put 119 dB into perspective for the lay-person:


That makes you a bit louder than a modern civilian jet airliner taking off at your neighbourhood airport and a bit quieter than the sound of freedom from your nearest military jet-base.

You might want to consider the following:
  • a curfew for your De-catted 4C to keep your neighbours on-side,
  • issuing free gas masks to those following you around as you spew all sorts of nasties into the atmosphere,
  • carrying an apology letter in your wallet to all of the greenies trying to save the planet by making the air that we breathe just a little cleaner.

I will get off my soap-box now.:geek:

Cheers,

Alf.
 

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Discussion Starter #19 (Edited)
Yes primarily, to be able to pass the emissions test. Saw this one from Flowmaster, 400 cell and only about 100 quid. With that on its own bypass/valve, open and my Quicksilver valve open to the resonator I get low emissions and quiet when I want it, full bore turbo back when I don’t 😁
111510

The other option I have is to just add it like a resonator to the straight through side of my Quicksilver so then valve closed becomes mot test mode. That’s tidier and requires no additional bypass and valve.
 

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Just to put 119 dB into perspective for the lay-person:


That makes you a bit louder than a modern civilian jet airliner taking off at your neighbourhood airport and a bit quieter than the sound of freedom from your nearest military jet-base.

You might want to consider the following:
  • a curfew for your De-catted 4C to keep your neighbours on-side,
  • issuing free gas masks to those following you around as you spew all sorts of nasties into the atmosphere,
  • carrying an apology letter in your wallet to all of the greenies trying to save the planet by making the air that we breathe just a little cleaner.

I will get off my soap-box now.:geek:

Cheers,

Alf.
Having a curfew for a de-catted 4c is an actual thing. I leave for work around 5:30am and sometimes dont get home till around 11pm, so instead of keeping it in dynamic mode all the time, I put it in natural mode and manuel mode and shift as low rpms as possible to keep thd noise down. It works pretty well.. My remote control valve doesn't work because it didn't come with instructions for the wiring, and the place I bought it from and the manufacturer have been no help, so its been left un-wired.
 
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