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Replacing the factory downpipe/catalytic converter


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Hey everyone. Been researching it but not found an answer yet - on my 2017 sti I’ve swapped out the factory exhaust for an invidia catback and it’s awesome. 

Is it worth swapping out the downpipe/ catalytic converter for a catted aftermarket in terms of performance, noise increase, emissions and road legal?

anyone who’s done this or got experience on this let me know.

 

cheers

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Hi. I love the sound of the invida exhaust almost ended up with a q300 my self but opted for a the Milltek and don't regret it. I was like a kid on Christmas day when I first fired it back up

I haven't yet experienced downpipe and sport cat myself but from what I've heard it's one of the best and yet to not to costly way to get easy power out of the EJ engine and its supposed to really bring it to life. I haven't heard a bad thing as long as you get it tuned straight after.

I also do believe it's still road legal as long as the main cat is in. But don't quote me as I'm no expert. I am looking at getting a Milltek downpipe and sport cat to finish of my exhaust system. In fact I am down at Scooby clinic next Tuesday getting a tune and I will ask the question about fitting a down pipe and sport cat

 

David

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Thanks David, that’s all really useful to know. Yea I was real close to taking the milltek so I get the appeal for you. The invidia downpipe is catted so that would be my choice for consistency in the system. Will be getting a stage 1 tune ASAP after to loosen up my engine the way it should. Let me know what the clinic says. Cheers

Steve

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I dont know about the newer imprezas, however the classics have a blanking plate on the turbo downpipe blocking the wastegate, causing restrictions to the flow.

Getting an aftermarket downpipe with a sports cat made a noticeable difference, especially when mapped, it felt sharper, more quick to respond, and of course the noise was better.

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On 5/15/2018 at 8:01 PM, Sevi said:

Thanks David, that’s all really useful to know. Yea I was real close to taking the milltek so I get the appeal for you. The invidia downpipe is catted so that would be my choice for consistency in the system. Will be getting a stage 1 tune ASAP after to loosen up my engine the way it should. Let me know what the clinic says. Cheers

Steve

Hi Sevi, spoke to the guys at Scooby clinic yesterday and they confirmed what I already said having the down pipe and sport cat will really open the car up and should still be road legal. 

Just had mine tuned with the following mods;

AEM cold air intake

Mishimoto turbo inlet hose

NGK 1 step colder spark plugs

3 port boost solenoid

Milltek cat-back 

This got me up to 317bhp but if I were to fit the down pipe and sport cat should be seeing 340bhp

Hope this helped.

 

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