Catted headers vs off road headers

I know you need the catted version if you plan on passing inspection. What are the other differences? Do you lose much power by having headers with the cats on them. Worth even doing...fill me in peeps

5starr0 said:

I know you need the catted version if you plan on passing inspection. What are the other differences? Do you lose much power by having headers with the cats on them. Worth even doing...fill me in peeps

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Deleting the cats is primary reason for getting headers. You won't see much of a difference if you still retain cats.

Do you only fail inspection on a visual inspection or will it fail emissions

VTECSAUCE said:

Deleting the cats is primary reason for getting headers. You won't see much of a difference if you still retain cats.

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This isn't true. Factory cats are very restrictive, yes, but the main reason for headers is the improved design and flow over stock manifolds. The difference between no cats and cats on a header setup is usually only a few HP with good high flow cats.

No cats equals failed emissions. No way to trick that one. Running high flow cats doesn't guarantee you'll pass emissions either, you have to talk to the company that makes the header and cat setup to see if it'll pass emissions. Each state is different as well.

Oh and high flow cats will keep a lot of raspiness out of the exhaust.

n8rfastback said:

This isn't true. Factory cats are very restrictive, yes, but the main reason for headers is the improved design and flow over stock manifolds. The difference between no cats and cats on a header setup is usually only a few HP with good high flow cats.

No cats equals failed emissions. No way to trick that one. Running high flow cats doesn't guarantee you'll pass emissions either, you have to talk to the company that makes the header and cat setup to see if it'll pass emissions. Each state is different as well.

Oh and high flow cats will keep a lot of raspiness out of the exhaust.

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In essence this is what I was saying. Perhaps it was poorly worded. The stock exhaust manifold is designed to flow only as well as the cats will permit, so deleting the cats while keeping the factory design wouldn't be ideal. But the same goes for changing the design to restrict it with cats. Why pay so much money and put in so much effort or pay more for the install, to restrict the exhaust with cats just to gain maybe a few whp? If you're going to do headers you might as well get the most of them, kinda silly otherwise IMO.

n8rfastback said:

This isn't true. Factory cats are very restrictive, yes, but the main reason for headers is the improved design and flow over stock manifolds. The difference between no cats and cats on a header setup is usually only a few HP with good high flow cats.

No cats equals failed emissions. No way to trick that one. Running high flow cats doesn't guarantee you'll pass emissions either, you have to talk to the company that makes the header and cat setup to see if it'll pass emissions. Each state is different as well.

Oh and high flow cats will keep a lot of raspiness out of the exhaust.

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Yup I agree.

VTECSAUCE said:

In essence this is what I was saying. Perhaps it was poorly worded. The stock exhaust manifold is designed to flow only as well as the cats will permit, so deleting the cats while keeping the factory design wouldn't be ideal. But the same goes for changing the design to restrict it with cats. Why pay so much money and put in so much effort or pay more for the install, to restrict the exhaust with cats just to gain maybe a few whp? If you're going to do headers you might as well get the most of them, kinda silly otherwise IMO.

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No totally wrong. First thing is realize the major difference between the factory cats and the high flow cats that come with headers. There is no comparison, the factory cats were designed specifically for emissions so they will restrict flow somewhat. High flow cats that come with headers don't do shit for emissions, really just cuts down on the raw fuel smell and as mentioned above they reduce the volume a tad.

Power-wise with headers there isn't much difference at all between off-road and catted versions, maybe 3-5hp. You will still see major gains with catted longtube headers over the factory header/cat setup.

Good info...I appreciate the input. Passing inspection limits all the fun from tint to how you run your exhaust

n8rfastback said:

No cats equals failed emissions. No way to trick that one. Running high flow cats doesn't guarantee you'll pass emissions either, you have to talk to the company that makes the header and cat setup to see if it'll pass emissions. Each state is different as well.

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Can you just tune out them out with a custom tune? Admittedly I don't know much about this.

I used to have a truck that wouldn't pass emissions because of never ending evaporative emissions issues. So I sent the PCM to a tune company and they basically deleted the system so it didn't throw any SES codes when they hooked up the OBD2 port.

I'm guessing this can't be done when removing cats because if you deleted out the o2 sensors you could mess up your engine?

The after cat O2 sensor is mostly measuring cat efficiency. You need them to be removed from the tune when you run headers or delete the cats.

Barrel said:

The after cat O2 sensor is mostly measuring cat efficiency. You need them to be removed from the tune when you run headers or delete the cats.

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So why can't they just be tuned out to pass emissions then?

The problem is the emissions test checks the actual exhaust, not what the computer thinks in the car. So aftermarket cats don't "clean" the exhaust as well as factory cats, and the emissions tests show it.

Rypkr937 said:

So why can't they just be tuned out to pass emissions then?

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They need to be on and active in order to pass. Having them off is an automatic failure.

n8rfastback said:

The problem is the emissions test checks the actual exhaust, not what the computer thinks in the car. So aftermarket cats don't "clean" the exhaust as well as factory cats, and the emissions tests show it.

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That's true only for smog checks. Typical emissions tests are run via OBDII and is completely through the vehicle's PCM. There is of course the visual check but no sniffer is involved.

For those that need to only pass the obd check you can use something like this:

http://www.amazon.com/gp/aw/d/B00AQ7972O/ref=pd_aw_sbs_263_2?refRID=07ZTVH4ARPQKVPRZSJ5R

Usually does the trick without having to turn the O2 sensors off in the tune.

It also depends on your state and its emissions standards. Here in WI you are allowed one readiness failure on newer vehicles. Anything greater than that results in a failed test.

On my last vehicle I had a tune that "tuned out" the o2 sensor readings. I had one sensor that would read "unsupported" by the emissions obd2. Becuase the readings only had one readiness failure, I still passed emissions. The other o2 sensor read fine because it was precat.