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Hey All,

I had to change out my power steering pump, and during the process I noticed that the manifold was cracked. Not a big crack but still. So I started looking at headers, and the consensus seems to be to spend the extra money on the Doug Thorley headers, lest you want to do this again in the near future. I also have come to understand that these headers will eliminate the first set of cats, which are the ones the O2 sensors do their before and after against. I live in an emissions checking state (GA) and while only once in my 20+ years of getting emissions tests done have I had someone grab the mirror to look under and see if the cats were there (the same jerk stopped and started the truck a few times because it was "old and sometimes people with emissions issues will reset the computer and doing that pops the CEL", which ironically I had reset the computer because I was having issues at the time, but still...), I'd rather not take the chance. I see that the headers have a place for the pre-cat O2 sensor so no issue there. I looked on the Magnaflow site (I have the Magnaflow cat-back) and their recommendation for the cat has the O2 sensor in the middle. So I have a few questions:

Has anyone done the DT headers and an aftermarket cat to stay street legal? If so what is your setup, and any gotchas or extras you had to do?
More of a general question, but if the O2 sensor is in the middle of the cat, aren't I losing half of the "cleaning" of the exhaust?

Thanks for any info!
 

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Curious as to whether long tubes or shorties are being discussed here...?
 

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Curious as to whether long tubes or shorties are being discussed here...?

I believe he Doug Thorley headers are sold as long tube. They are the only option available for this truck. To my knowledge, no aftermarket headers allow the use of the primary cats. I could be wrong.

In theory, you could remove both sets of cats and do DT headers then custom pipes, with cats on them, between the headers and y pipe. You would have to relocate your downstream O2 sensors to after those cats.

If the purpose for all this is to remain emissions compliant you probably still don't achieve that. I don't know about GA but most states' vehicle codes are written to say that any deviation from stock equipment is a violation.
 

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You could always tack the outer shell of a cat onto your pipes if you have o2 spacers to fool the obd2 and they aren't sniffing the tailpipe. Don't see why that wouldn't pass a visual inspection as long as you make the tacks in discrete places

On a side note one set of real cats (not high flows) should be efficient enough if they are sniffing the tailpipe
 

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Doug Thorley only makes long-tubes for the 3.3L and they make short and long for the VQ40DE. There are other options for the 3.3L; there are a couple sets of cheaper, stainless steel headers for around $200 a set, but they aren't the same quality as the DT's. Pacesetter, Dorman and Magnaflow make a sort of header/catalytic converter hybid that's one piece and replaces the factory manifold and front converter, as well; they seem to fall into the $600-$700 a pair range, depending where you get them from.
If you use the DT's, you can still run the rear cats (if you have them), but if you want to use them as your "monitored" converters, you have to have an O2 sensor bung installed behind the converter and lengthen the wires to the rear sensor. Most will delete all four converters and use a 90 degree CEL eliminator for the rear sensor. Of course, where you live and the state inspection practices will dictate what you can get away with. Keep in mind that the headers for the 3.3L's are always advertised as "For off-road use only." If you live in California your best bet is to stick with stock exhaust unless you only drive "off-road."
FYI, for those with V6 2nd Gens, the DT shorties are a direct bolt-in and pending C.A.R.B. certification. The long-tubes are considered "off-road use only" and if you plan to install them (meaning front converters will be deleted), you will need to get a new ECM tune for the engine to run properly (UpRev is the most popular choice).
 
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