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Discussion Starter #1
Recently installed the SRS catback, next step is the downpipe and stage 2 AP. Question is, what is the Best DP IN YOUR OPINION for PA emissions/inspection.

From what ive heard, read. PA is strictly obdII and gas cap testing. But some places do visual. And it all depends where you go.

Ive also heard issues on boost creep with catless DPs.

Any help or opinions are appreciated. As of now, I believe I have 2 in mind. Invidia v2/v3 bellmouth (catless) or the Helix Catted downpipe. What are the advantages of one vs. the other?

And from what ive read, either should mate flawlessly with my catback due to the 3" flange being the same on both.

Thanks guys, sorry if my questions a little jumbled :confused:
 

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Some cars creep, some don't; it's usually more of an issue with the 2.5L engines.

You need to find out the inspection method used in your municipality before deciding on which downpipe to use. A catless downpipe will make more power than a catted one simply because there is less restriction. Will it be something you could really measure on a stock turbo? Probably not.
 

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A catless downpipe will make more power than a catted one simply because there is less restriction
True, but negligible. I believe it was tested by Cobb and found that a high-flow cat dropped the power output by less than one whp (dyno error). Though, it could be that Cobb is simply trying to promote the catted DPs....
 

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Discussion Starter #4
Some cars creep, some don't; it's usually more of an issue with the 2.5L engines.

You need to find out the inspection method used in your municipality before deciding on which downpipe to use. A catless downpipe will make more power than a catted one simply because there is less restriction. Will it be something you could really measure on a stock turbo? Probably not.
In your opinion. Which downpipe do you have/would you use? Just looking for some feedback on the many downpipes. My friend said his mechanic will pass me as long as I have no CELs. I've heard invidia is good. Not too pricey either.
 

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True, but negligible. I believe it was tested by Cobb and found that a high-flow cat dropped the power output by less than one whp (dyno error). Though, it could be that Cobb is simply trying to promote the catted DPs....
Yeah. Even from a green thumb pov that seems to be the issue there. As far as catted DPs go I see many with the helix catted dp. How has it been for anyone with it? I notice it also comes with a wideband o2 sensor bung. Does this mean I then need a wideband o2 sensor? Ahhh :confused:
 

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Bblue Rrex said:
In your opinion. Which downpipe do you have/would you use? Just looking for some feedback on the many downpipes.
They all perform about the same.
 

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True, but negligible. I believe it was tested by Cobb and found that a high-flow cat dropped the power output by less than one whp (dyno error). Though, it could be that Cobb is simply trying to promote the catted DPs....
There's no way that you can do two runs, even on an exact dyno and exact conditions, and expect to pull a statistic like that, it's post hoc logic.

However I will give that I BET you won't EVER notice the difference between high-flo cat and catless w/o more engine mods than a Stage II.
 

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There's no way that you can do two runs, even on an exact dyno and exact conditions, and expect to pull a statistic like that, it's post hoc logic.
Which is why I stated "Dyno error."

What is meant is that two runs, one whp difference we serve up to error between the dyno runs.

Q.E.D. ;)
 

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If they do a visual inspection, you will fail with either downpipe because they are not DOT approved. Power-wise, you'll feel no difference between the 2. Even a catted DP may throw a P0420code which will have to be taken care of to do an OBDII inspection. I would make sure about your inspection process before you purchase anything, or become good friends with an inspector :)
 

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I believe so but I don't know if it passes the monitors or allows the vehicle to perform emission self tests, which is the other thing that the OBDII test looks for. You may have to call COBB for that answer unless someone else has an idea?
 
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