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2004 2.5 RS
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13 Posts
Discussion Starter · #1 ·
i just purchased a stromung cat back exhaust and i want borla headers. some people have told me not to get headers because its easy to mess up the o2 sensor changing headers. I would juts like to know if anyone came across this problem going from stock to borla and if you did how did u change it. thanks

Evan
 

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12,196 Posts
There's no o2 sensor in the header. You might get a P0420 code (catalyst inefficiency), which can be fixed with an MIL eliminator, o2 spacer, premium gas, header wrap, or a combination.

/thread

:)
 

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00 2.5RS BRP
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687 Posts
the fact that the exhaust can free flow instead of causing backpressure can increase mpg *a little bit*....but if your like me you wanna hear the rumble and step on it more...which means horrible mpg :D
 

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Taking the average 25mpg and multiplying by 9% gives you about 2.25, which would be 27.25 mpg average. I don't think it makes that much of a difference, IMO.. but I guess it's possible.
 

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2001 RS 2.5
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640 Posts
im running UEL headers, 04 WRX cat back, WRX-RA Trans (higher rpms on fwy) and I'm now getting the best mileage ever. The RA Trans I guess puts the car at a higher RPM that has more torque so i give it less gas?

I dono, but I am now "NOT READY" anymore cause of the P0420, but am getting great mileage.
 

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99 Legacy L 30th Anniversary
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64 Posts
The HFC will make your MPG suck. And you don't really want to not pass inspection do you??? Just the stromung CBE alone would raise it a little, but not enough to make a difference. And the only way you get it is if you baby it and you do like 15mph under the speed limit lol :D As for the Borlas, I'm not too sure, because i'm in the process of getting my borla replicas, but everyones sold out and none are up on ebay at the moment.
 

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13 Years of RS
2005 Toyota Corolla :(
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5,532 Posts
No, but you won't pass emissions, and your gas mileage will suck.
Not necessarily true about the gas mileage. I have an AVO turbo kit with it's high-flow cat on my car, and I get the P0420 quite often (about every 100 miles), yet I'm still getting 26-28 MPG on a tank of gas. Stock manifold, AVO up and down pipes with single high-flow cat, stock midpipe, and Stromung axle-back muffler. Really need to upgrade that midpipe, it's like a cork right in the middle of my exhaust.
 

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OG GC
MY00 BRP RS...still adding to
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4,471 Posts
/\ +1 about the mileage.
I have wrapped Borla reps, R/T HFC, Custom mid, and a Prodrive axleback. I, too get a CEL every 150 miles. But I have no issues with crap for gas mileage. :confused:
 

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2004 2.5 RS
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13 Posts
Discussion Starter · #15 ·
thanks for all the info.. so i should be fine with all the check engine lights and stuff is i just get the borla headers with my stromung catback?
 

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2004 2.5 RS
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Discussion Starter · #16 ·
and im not too concerned with the gas millage too much.. i just dont want the check engine light to come on lol
 

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2017 WRB BRZ w/PP
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1,739 Posts
I don't know where all this stuff about horrible gas mileage is coming from. I have Borla replica's, RT HFC and a Borla CB and I get 28-30 mpg's on the highway.
 

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13 Years of RS
2005 Toyota Corolla :(
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5,532 Posts
Do what I did to deal with the CEL: get a ScanGaugeII. Now, when my CEL comes on, I can scan it, see what code it is, and clear it in less than 10 seconds without even slowing down.
 

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2000 RS SRP
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199 Posts
so whenever a cel light comes on the car will automatically run richer and what not and cause bad mileage or is it only for certain cels? I have a scan gauge with my borla setup and I might as well leave it on if it isn't going to affect anything.
 
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