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Discussion Starter · #1 ·
im having a hard time deciding what size dp to order. i originally was going to buy the 3'' zzp dp. talked to a few friends and now they have me second guessing myself.

would 3'' hurt me? keep in mind i plan to go 2.5 catback.
 

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im having a hard time deciding what size dp to order. i originally was going to buy the 3'' zzp dp. talked to a few friends and now they have me second guessing myself.

would 3'' hurt me? keep in mind i plan to go 2.5 catback.
go with the 2.5" downpipe, cause when you go from 3" to 2.5", you start to restrict the flow of exhaust. keep it uniform
 

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Discussion Starter · #3 ·
what if i ran 3in all the way back? lol i dont plan on it but would that kill me?
 

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what if i ran 3in all the way back? lol i dont plan on it but would that kill me?
a three inch would be too tight under the car to be feasable. i do believe one person has done it, but to be worth it, stick with 2.5"
 

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Discussion Starter · #5 · (Edited)
k...one more ? does the cat really make the car sound 'ricey'

P1mpsy0r1c3 added 1 Minutes and 34 Seconds later...

i mean w.o. the cat does it sound 'ricey
 

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k...one more ? does the cat really make the car sound 'ricey'
the cat is not what makes the car sound "ricey", the muffler does. Or should i say the construction of the muffler does. and how the motor is set up can do it too. I just put a cherry bomb on my car in place of the resonator, still have the factory cat, and the car has a mixed tone to it, half rice, half domestic muscle(an inline four will never sound like a muscle car, it is because the way the cylinders are set up, is as to the note of sound that comes out the rear.)
 

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Discussion Starter · #7 ·
well i dont wanna run with the cat, but i head w.o you need some tuning...any truth?
 

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well i dont wanna run with the cat, but i head w.o you need some tuning...any truth?
you remove the cat, you will throw a CEL. The cobalt employs a dual O2 sensor set-up, and if the mixture to the second sensor matches the mixtire read at the first, it will think the cat is not working, and throw the code. I have heard O2 clamping may solve the problem, but am not a believer, aand i highly doubt you can tune the car enough to ignore the second sensor. My suggestion, go with a low restriction cat(high flow), they have been tested and proven not to throw CEL's on newer cars, while letting as much airflow through as possible. We followed the order of one customer, whom we warned about the issue, to remove the cat, so we did. sure enough, he came back the next day, and had to have a new cat put in, because it threw a CEL. Put in a new cat, clear the codes, and it was fine.
 

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Discussion Starter · #9 ·
so would the XTC 2.5 dp be good? havent been able to find zzp 2.5
 

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so would the XTC 2.5 dp be good? havent been able to find zzp 2.5
website?

i havent had to do a dp for a balt yet, so i dont have stats for them. I do believe they would, you doing a header, or gmpp mani?
 

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Discussion Starter · #11 ·
i have CA header. i was planning on doing dp, then catback...idk much about 4 cylinders and downpipes.
 

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i have CA header. i was planning on doing dp, then catback...idk much about 4 cylinders and downpipes.
remember, if you do any exhaust job, you need the cat.

since you have headers, a dp will help with the airflow.
 

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Discussion Starter · #13 ·
what do you mean exhuast job
 

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you remove the cat, you will throw a CEL. The cobalt employs a dual O2 sensor set-up, and if the mixture to the second sensor matches the mixtire read at the first, it will think the cat is not working, and throw the code. I have heard O2 clamping may solve the problem, but am not a believer, aand i highly doubt you can tune the car enough to ignore the second sensor. My suggestion, go with a low restriction cat(high flow), they have been tested and proven not to throw CEL's on newer cars, while letting as much airflow through as possible. We followed the order of one customer, whom we warned about the issue, to remove the cat, so we did. sure enough, he came back the next day, and had to have a new cat put in, because it threw a CEL. Put in a new cat, clear the codes, and it was fine.
There is an 02 simulator that i found and have used before that works really well if you don't want a cat it sends back the proper code telling you engine that your cat is working perfectly:D here is the link O2 Oxygen Sensor Simulator - Bypass by Oxygen Simulator Performance Parts
 

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what do you mean exhuast job
redo the exhaust, anything from a muffler and tip, to full system(front to back), is defined as an exhaust job. your dp, and cat back exhaust system, is termed as an "exhaust job"
 

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a few things about this, 3" is WAY too big, don't go over 2.5". I had the XTC downpipe on my last car, and it was good. NOT having a cat will make the car louder, and sound more ricy. If you choose not to have a cat, you can simply have someone turn off the rear 02 sensor with HP Tuners. No need for any kind of tune other than that.
 

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my friends rx8 he took out the cat and lost a sum power and the guys at greddy recommended him to put the cat back on cuz u need the back-pressure...Im thinking bout replacing my cat with a high flow cat which wont make it sound too ricy but it will help with the flow and still maintain enough back pressure...dont know if it helps or hurts the HP on our cars i know it helps on rotary engines tho...haha
 

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a few things about this, 3" is WAY too big, don't go over 2.5". I had the XTC downpipe on my last car, and it was good. NOT having a cat will make the car louder, and sound more ricy. If you choose not to have a cat, you can simply have someone turn off the rear 02 sensor with HP Tuners. No need for any kind of tune other than that.
you do that. And let me know how long it takes before you decide to turn it back on and out in the cat again.

my friends rx8 he took out the cat and lost a sum power and the guys at greddy recommended him to put the cat back on cuz u need the back-pressure...Im thinking bout replacing my cat with a high flow cat which wont make it sound too ricy but it will help with the flow and still maintain enough back pressure...dont know if it helps or hurts the HP on our cars i know it helps on rotary engines tho...haha
that's precisely the problem with the cobalt, loss of backpressure, loss of power.
 

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