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I've been digging into my recently purchased '91 4.0 HO, working to get the recurring exhaust smell troubleshot. It was obvious immediately that the tailpipe and muffler were toast, but after getting them replaced, I was still getting fumes. I finally determined for sure the exhaust manifold is cracked by sticking a mirror and a flashlight in there for a detailed inspection this morning (After two mechanics and a muffler shop said it was fine). The truck has not been registered in California yet. It still has almost a year left on a Georgia plate registration. Here in CA we have C.A.R.B. which typically only allows the stock (more restricted) manifold design. I am all for clean air and smog sucks, but I don't understand how increasing the efficiency of a motor by improving the flow design on a header makes for significantly more exhaust particles. Maybe someone has an answer... More importantly, does anyone have any experience with getting an inspection in CA? I'm sure the stock design with the improved materials/welds will work fine, however I always install the best performing and highest quality parts I can find within reason. Wondering if anyone has any suggestions on which header to use or if there is something I am missing... I've found about six or seven different designs so far on Amazon, Ebay, and the like, but only a few stock designs that are C.A.R.B certified... Also, will a redesigned, less restrictive header increase the chances of failing a smog? I'm guessing that it might fail a smog with the cracked header on it now. Thanks everyone... :cheers: