Definitely clean up what you see... Absolutely.

But, I don't want to smell anyone's exhaust out in the woods, on the trail, or around the campsite either.

Me either that's why I always go solo. I think after your project is complete and TUNED you'll know what fully combusted gas is. Most Exhaust pollution is caused by ignorant people that don't understand combustion and organic chemistry including the mechanics they trust. This bring me back to my college days. Here is the real science, all you need to know. Fully combusted. Fuel (CxHy) + oxygen (O2) + spark>water (H2O) + carbon dioxide (CO2) + heat. The product compounds are odorless. 😽 Let's put catalytic converters composing of rare earth metals on greenhouses too, tearing up the earth some more.
Tell your friends and help the problem at it's root source. No more myths to pass along.

What do you mean by tuned? Other than OrangeVirus, I don't know of anyone offering real tuning for these trucks... And even then, OrangeVirus is just in beta at the moment.

There are a hundred different variables involved. The only two things that matter for tuning are timing and a/f ratio. Modern scanner like the SCT Raptor and an ACCURATE, REPEATABLE & CONSISTENT AIR FUEL RATIO DEVICE. More expensive Horiba, ECM or Powertrain Dynamics Dyno sensors are required. I'm sure you can find a good Dyno tune shop.

That's great, is there a specific manufacturer you'd recommend for a tuning device for the 4.7L V8?

So, to recap...

I'm looking at DT Long Tube headers with a DT y-pipe. I'll need 2 cats (looking at magnaflow 54956) to replace the resonators in the y-pipe by cutting & welding. After that I'll need O2 bung plugs & O2 bungs to weld downstream of the cats on the y-pipe.

Sounds right?

I had my RHS exhaust manifold replaced a couple weeks ago. After looking at all the options including the DT headers (hard to find, but still available in a coupla places), and in consultation with my mechanic, I just decided to get a normal genuine Toyota manifold/cat. It took about 110k miles for mine to crack, so if I get another 110k before I have to replace that one, it's not too terrible.

The mechanic asked me what I like best about the V8. I said, for sure it's the huge amount of torque available at very low rpms, like 1-2k (even on the highway, I rarely if ever see 3k rpm). He said, then stick with the OE part because while the headers would surely be more free-flowing and ultimately increase peak torque and hp, they will most likely shift the torque curve to the right. So you'd get more torque but higher up. Impossible to tell how much without a dyno, but point taken.

At any rate, the car is soooooo much quieter now, especially on startup.

I'm sure your mechanic is right. From what I've been reading, the short tube headers = +++low-end torque. The long tubes = +++peak power (shifting the curve to the right).

With that being said, OEM parts are more expensive than they should be. I'd rather drop what I have saved on parts that won't crack, will sound better, and will ultimately save a little $$ with some extra mpg.

I understand that my 4Runner is no race machine.. I do use it to tow but it's got an excess of low-end torque that I rarely use, so I'm willing to give that up for the LT headers.

Yup. Here's what I used:

Plug: https://www.summitracing.com/parts/stw-o2p
O2 Bung: https://www.summitracing.com/parts/kok-9002s-c

Has anyone accomplished a true dual exhaust on a 2020 5th gen 4Runner?

Resurrecting this thread. I having a 2004 GX470 (essentially a later model 4Runner). I found a TRD supercharger out of a 2003 Sequoia that got T-boned pretty badly. I decided that, if I’m adding more exhaust, I should install the Doug Thorley headers to allow exhaust gases to get out a little easier. I have the long tube headers sitting in a box. However, I live in the front range of Colorado which has fairly strict regulations on Emissions. I have had difficulty even finding a shop that’s willing to install aftermarket exhaust which isn’t OEM specs.

I have had poor experiences with air care Colorado previously. I had a souped-up Subaru with a JDM STi drivetrain swap that was done in another state along with a full exhaust system with high flow cats welded in to make sure it was legal and I wouldn’t get hassled. When I moved back to CO and tried to get emissions done, the numbers were great and most were well below stock allowances. However, the guys working there could tell it had been fairly well modified. They got out the inspection mirrors and failed me on “visual inspection”, because my catalytic converter‘s were not in the exact same places as the book described. Total BS to me.

I would like to install my long tube Doug Thorleys and also have cats welded in where the resonators are in order to at least attempt to be legal. Any recommendations for the most compatible cats? Any install do’s or don’ts? Has anyone done this in Colorado?

When I ordered my DT long tube headers I also ordered the magnaflow y-pipe. It is mandrel bent and you have the option for Colorado compliant catalytic converters. I don't live in CO but they have that option.

I have heard GESi are the best cats for performance. Whether or not they put out clean numbers? The state you're testing in probably has a lot to do with it.

There is a Lexus GX fb page called GXOR that will most likely have more info on this. The creator and admin has a lot of mods and exhaust work done on his.
Not a fan of social media, but I have several pages I follow for info like this.
He also has a web page GXOR