I was wondering if anyone knew of any legal headers available for the 3.7L. If not, is there anyway I could modify existing headers to make them legal (adding cat after headers). I live in NY if anyone wants to know that.
Well the NYS emissions check is done by scanner. They check for any out of range readings.
Here's the link to the NY DMV page regarding smog tests New York Smog Check and Car Inspection | DMV.org
Federal Emissions laws state you cannot relocate the cats from their original location. A header will remove the front cat or move the cats further downstream making them technically illegal in all 50 states. Any state that does a visual inspection will fail you if they know what they're looking for.
The type of cat has nothing to do with it. Technically it is illegal to relocate them, which cannot be avoided with an aftermarket header, like Freeballin said. Even if your truck passes the scanner test, they can still fail you if they want to.
However, I would think it is more than likely you will be able to find a shop that won't care as long as you pass the smog test.
Why not just keep your stock manifold just for the inspection? Should only take about an hour to change out. Unless they do random inspections or something I can see it being a problem but if you know when they are inspecting it you can just change out and then back once done. Right?
Don't worry about it. The laws are basically the same as Connecticut in New York and I didn't even get hassled with the supercharger on my truck. I have a longtube header to a 3" exhaust with one high flow cat and a muffler. As long as there is no codes and at least one cat. on there which you have one in the factory midpipe. California is really the only place you would get crap over it because they require 2 cats that are different than any other state.
New York law is like California. Sure they do the scanner but they also do visual inspection prior to the scanner. NY & Cali are the two most strength states in the country. A header is illegal for a couple reasons. The header changes the exhaust temperature so the temp going to the cats will be below specs. Same reason you can't move the cats. Like @Jesse said keep your stock manifold and put it back on for inspection. I do the same thing and I also replaced the 2nd cat with a pipe. So I reinstall them both for emission testing.
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