I have an idea that I'm not sure is legal or not.

I want to upgrade the factory exhaust to a 2.5 inch diameter true dual setup. However because I live in California I want to keep the secondary catalytic converters.

So the idea is yank the midpipe off, chop the secondary cats off, and modify the openings to accept 2.5 inch tubing.

I haven't been able to find anything that says it's smog legal or not. Can anyone advise me?

 

according to state's smog law, any cat after the second o2 sensor will not affect the smog check condition. My cousin own a shop (including smog) had verified me about it already.

 

Keep the secondary cats but chop off? Are you putting them back on?

I cut off from after the secondary cats and went x-pipe to true dual, passed smog with no issues.
whitebeast has heard my car =P

 

Sorry let me better explain.

I want to run 2.5 inch pipe from the primary cats to the secondary cats, modify the openings of the secondary cats to accept 2.5 inch, then continue running 2.5 inch all the way to the rear.

 

This is a 350, yes? And what do you plan to do with the mid out to the tail? I'd suggest you include a crossover pipe positioned as far forward as possible to reduce the chances of droning.

This Borla product comes to mind...
this is 2.5" but they make the same in 2.25"
https://www.borla.com/products/proxs...t__400493.html

 

It's a 350. Basic break down will be exhaust manifolds, 2.5 inch tubing, secondary cats, borla xforce muffler with a built in crossover, more 2.5 inch tubing, magnaflow mufflers in the rear.

Should be a nice flowing quiet exhaust. As long as it will pass visual smog I'm happy.

 

I had issues with spacing when I did mine, hope yours comes out nice, good luck!

 

Having ran V8's most of my life and never had drone issues, anyone care to repeat the past?
Simple setup; axe the secondary cats for the Borla crossover 2 in, 2 out. Fit some mufflers near the crossover about where the resonators are now and the rest is straight pipes to the tips. No rear muff past the axle.

So the question is, is it the firing order causing the drone or will getting the muffler back by the trans have it act as a resonator? And with the crossover, I think it will work.

Passing smog inspection, maybe not for the visual part.
Thoughts?

 

Well that's the kicker. I want to be able to pass inspection.

So at least the shells of the secondary cats need to be in place.