Educate me:
Why the long tube headers don’t pass emission, or produce more emission?
My understanding is that: Long tubes provide less restriction for the hot gases to exit the cylinder heads. With all the tubes of equal length, all cylinders will have the same restrictions and performance will be the same across all cylinders. Hence my question, where is the new emission gases come from?

 

Its not the measured emissions. Its the "modified" location of the cats. Federal law prohibits "modification" in any way to the cats. That includes location. The vehicle must stay "as certified". So it would be the visual part of the testing that would fail even if the sniffer said its OK. That's the way it was explained to me.

 

Why don't aftermarket suppliers then place the hiflo cats in the original location on their systems to prevent this B-S.

 

In addition, the headers can result in various CEL lights and codes. Many of these are based on ECM computations, such as comparing the temps and O2 content between the front and rear sensors.

 

.....because you can't engineer a long tube design with an integral cat in the space avaliable.

 

There's no "B-S" about it. If you want long tube headers then the location of the cats will change. Something has to give. They all come with the disclaimer "Not for use on polution controlled vehicles" or something to that effect.

 

Can you elaborate farther?

 

As was said, although a vehicle with long tube headers may pass the sniffer test, it would likely fail a visual inspection (assuming they check and assuming they know what they're looking at). This is due to the relocation of the cats.

Why (you might ask) would a header equipped car that's able to pass a sniffer test still fail based on a visual inspection showing the cats were relocated....my LGM headers with high-flow centers (as I understand it) are 2-stage cats (OEM cats are 3-stage). My cats are relocated further back and accordingly will take longer to heat-up and fire. It is said that during this extended heat-up period is when your car will pollute more than a car with OEM cats.

A question also comes-up with OBDII compliant vehicles....I've been told emission test stations will now forego a sniffer test and merely plug-into the PCM to check I/M readiness monitors and check for codes. If everything is OK it should pass. My C6 with headers does not throw any codes. My local emission test station, however, did not check the PCM on my OBDII compliant Suburban....they still put it on a roller and spun it up to speed doing a sniffer test. Are they just not equipped to perform the newer 'plug-in' test?

It's funny, I believe they allow car manufacturer's to meet CAFE gas mileage requirements by allowing one low-mileage model to be offset by other more efficient models they produce. I also think they allow utility companies or other large manufacturers that have a polluting facility to in effect 'offset' that facility with other facilities they have that do meet pollution standards. Why don't they apply the same options to individuals? IMO it's just another example of large financial concerns being allowed to bend the rules while the average taxpayer cannot do so. I'll put my soapbox away for now.