Decat pipes

Some do , some don’t ,

It’s a personal preference,
Decat means on and off once a year for nct which can be a pain
 
My personal experience: Sports Cat (that passes nct) saps about 10-20bhp and spools a little bit slower. This was the data got from the dyno. With a decat, the spool is a bit quicker and you also get a fair bit more sound. As you push for more power, more gasses need to exit quickly and the bottle neck becomes the catalytic converter.

From a practical point, a sport cat is much easier to live and no messing about with swapping cats etc twice per year :)
 
Yeah would be a pain the hoop alright.. debating is worth the hassle or not.
Even debating changing to UEL headers or not
Is your car mostly a road car, a track car or does it do both? If you are chasing times around a track, then every Bhp counts.

A 300-350 bhp Impreza is potent on the road and will spool quickly such that it's a fair bit of fun on the road. Push it north of 400 bhp, then the Sports cat will become more apparent when it is on the car. Over 500 bhp, it's a significant bottleneck to the car performance and you will feel it when you floor it.
 
I’m confused, the unequal length headers are what give the rumble , the equal length are the twin scroll ones
Baz not gonna lie . I'm a few cans deep.

So yes, you are right - I have Equal length ( no rumble) tiny bit down low. Which I have

Kinda wanna change but dont want to cos it's runs pretty damn well.
 
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