I was thinking about putting on a Flowmaster or Volant exhausts and cold air intake but was wondering what my 4R would sound like? I don't want it to sound like a little import car burping around the streets. I have the 4.0 liter engine in the 4R and just trying to get back some MPG from the mods I've done over the weekend.

For the 4.0, I would gow ith the Gibson, or a flowmaster. The thing I don't like about flowmaster is they drone. I've had a few cars with them and they all did drone around 3000RPM. I had a Borla on my 944 and LOVED it, but it was very loud. It was a cat-back with the Borla XR-1 muffler. Magnaflow - I"ve never had much luck till my Mr2 with keeping a nice deep sound. I did have to use a 27x6" round muffler to do it though. because of the mixed results, I wouldn't recommend one unless you hear one you like and know exactly what size muffler they have on it. One more thing... magnaflow drones too.

As for the CAI, I'm not a big fan. The stock system is a CAI and a pretty good one... unless you just want the look I wouldn't touch it. TRD sells an air filter for the stock box if you want something.

For mine, I just want something that doesn't drone but will make a nice rumble when you get on it. I've heard videos on youtube of the gibson on the tacoma 4.0 and talked to a few people around the board and everyone loves them on the 4.0. I'll probably go that route.

Listen to these with good speakers.
Magnaflow on 4.0: http://www.youtube.com/watch?v=G5uLCxmsRkY
Gibson on 4.0: http://www.youtube.com/watch?v=_lmFXUUBYnw (forward about 1/2 way through)

volant doesnt make it for the 4.0

like the guy said. keep the stock one and rip the carbon filter out. doing so will slightly increase ur performance and noticble response

i just replaced my cherry bomb vortex with flowmaster super 44, its alot more deeper. but the owner told me the flowmaster have alot of problems, he said that they put too many welds inside the muffler and it starts breaking apart, ill have to see how long this will last, the cherry bomb started to crack on all welds and i have email them, no respond. 3 years of use and it goes bad. if this flowmaster craps out, i will go with borla or magnaflow, the stainless steel is more better. also the installer/ owner recommend them, it laster longer and lighter.

I'd be interested to see how much mpg you actually get back with a free flowing exhaust. I would bet not much. Anyone else have any insight on this?

Doubt you'll see mileage - maybe 1MPG, but not much. Most people do it for the sound.

Part of the problem is the cats. You have 3 cats on the truck like the 2gr-fe engine. Below is a pic of a header vs. stock. IF you remove those cats and place a header in there with a decent-flowing exhaust it'll be a LOT more potent.

By removing the cats (all 3) on the 2gr-fe and just running a Magnaflow muffler we pushed 289HP at the wheels (everything else stock)... that's more than Toyota rates it at the crank! I do think the 4runner would respond the same way, the only problem would be the CEL light.

On the 1grfe we have 4 cats. two on the exhaust manifolds and two in the y pipe. I got rid of the front two and was very pleased using the 1st gen of DT long tubes as well as changing to a hotter tune on my truck. I'm updating to the 2nd gen which is slightly bigger overall. I'd say if you want real power get rid of the cats. APR told me when testing the factory muffler flows very well on our trucks. As far as CAI AFE or a 1st gen TRD is the best. K&N is ok on a budget but takes longer to get to ambient temps. For many the stock intake with a dry flow filter and removing the carbon filter is good enough. If you want sound a CAI and a muffler will be fine. If you want good MPG's these will really won't do anything really unless you change the way you drive. Stay below 2500 rpm and you'll get good MPG even with stock parts.

Are there o2 sensors to tell if the front cats are there and working or can they just be pulled without a code? I'm seeing URD has an o2 simulator, so I'm guessing you have to add that for it to not throw a code.

The four O2 sensors only monitor the first two cats in the exhaust manifold. if you got rid of the rear cats in the y pipe the CEL won't come on. If you have the APR X1 the CEL won't come on. URD have a o2 sensor sim for when you have long tubes and the CEL won't come on when your running long tubes. As for leaving them in YES!! For me thats how my X1 monitors the health of the engine.