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Team after selling my impreza back in 2015 I have returned to the fold. I now have an R sport 2.0L non turbo hawkeye model year 07. It sadly curentnly only has an equal manifold on it, I have the parts in mind to change this situation, however I was wondering if anyone can recommend a decent custom exhaust fitter within Cornwall or Devon. I'm aware of the problem adding an unequal header can cause as I don't want to throw any ECU lights up so it may also need a remap. Any advice would be great fully received. Regards Rich. 

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Welcome back

Having tinkered with NA bikes over the years having unequal length headers will cause performance issues as the NA engine cylinders need a specific length for pressure waves coming back (back pressure) to the cylinder. For a turbo engine it is not as important

my 2p go for a cobra manifold back system, sports cat or decat or cheaper would be the cat back option? 

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Jay thanks for taking the time to reply buddy, I hear what you're saying about back pressure, it could indeed be a problem in the NA engine, and I also hear what you're saying about back pressure post turbine in turbos, plus with hot and cold the pressure difference is always going to provide a good back pressure because that is a how a turbo functions, its always going to be greater than ambient, my thoughts to combat this thought was to just use a performance cat whilst removing all other flow bottlenecks? Any thoughts on that?

I will admit I'm not completely in the dark here in relation to such things, as I have six motors or various BHPs but I have to admit I have never placed an unequal header before on an engine which has been fundamentally designed to run with an equal header length on it.

Scary times indeed. 

My ideal currently is that standard equal headers on the car currently has both the AFR and 02 sensor living in the header area (as that's where the first cat lives also), the Air Fuel Ratio (AFR) sensor lives there (before the cat), then its the first Cat and then the 02 sensor (known as the Lambda) after the cat, this is so the car knows what products its pumping out to air. This is where potentially things will get messed up in relation to fuel and unburnt products remaining in the camber (if the back pressure isn't scavenging that correctly) for it to all exit as it currently does with the equal headers.

My aim is to fit a unequal header, with the AFR in it still as before (before the cat), then a high flow cat (to ensure flow is still keeping things moving) and then as previously (and as it should be), have the oxygen sensor just after the high flow cat. This should in my brain mean I don't need a remap, or to delete anything from the ECU, (I stress in my brain that this works in theory).        

Any thoughts?

Thanks for your time man.



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My advice would be to chat to scoobybits about it, out at Wheel Busy. I dont know where in cornwall you are, but people seem to travel to them, since they are probably the only specialist subaru garage in Cornwall
Jason knows his stuff, and has so much modified cars through there, he will likely know what works and what doesn't.
They are also an authorised cobra exhaust centre, so if you decide to go down that route, they are the "go to" people.


(I am in no way affiliated with them or receive money for promoting. haha)

If you are towards the north of the county, I would probably recommend Engine Tuner, in Plymouth.
They have been working on Subaru's for many years.


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I have emailed them already buddy and I'm awaiting a reply. I'm a big believer in admin so to speak, and hopefully that will show up with a reply, thanks for taking the time to reply to me. I appricate it. 

As for Plymouth it's not super far. I will give then a Google search now. 



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