This is for all those guys out there who have been reading the recent posts of performance mods marketed towards the 5th gen 4Runner crowd.
There are realistically only a few claimed ways to improve power or efficiency on a 5th gen 4Runner. If I left any out please add them below. They are:

1. CAI
2. MAF Spacer
3. Running High Octane fuel
4. Exhaust mods
5. Reducing GVW and unsprung mass
6. Driving smarter

I did not list the supercharger because it does not exist for production nor are there any turbos. Now, let's get one thing straight: This post is not to judge people. I don't care, nor does anyone else, how much money you spend on these mods. As a matter of fact, let's pretend they are all free (in this discussion) so that takes money out of the equation. Alright? For the purposes of this discussion let's just talk about whether they work as advertised. Also lets keep this thread civil and educational because, in my opinion, there is too much "he said" and "hearsay" in the other threads that clouds the judgement of our less experienced members.

One more thing: Lets keep the testimonials out of here. I hope everyone sees the fallacy of reading one - or even ten - guys experiences using these products and thinking it is hard science. I don't know how many times I have read "I just ran through half a tank of fuel and my mpg indicator went up two mpg!" Please realize these type of comments mean absolutely nothing to anyone other than the guy typing the post. We all drive different and will see different results. That's why hard data is so important and also almost non existent. Don't get sucked in by reading a few guy's experiences. How many reading this have read the dreaded "mpg" threads? Holy cow, some of these guys can't even calculate their mpg the correct way! Are you going to trust them on a performance mod? Reading the "mpg" threads there is a huge difference in individual owners vehicle efficiency. Are the vehicles really that different? No, but the owner's driving style and routes are and that is what makes up the discrepancy.

Lastly let's discuss human nature for a bit. We are a proud bunch. If I go out and spend a lot of time or money on something (stereo, suspension, paint job or other custom item) I am going to be proud of it and want to show it off. We are all like that. Human nature. I will also go so far to say that, after spending a ton of time or/and money or a mod, I will convince myself that it works much better than what I had. Why? Well, it HAS to right? I just spent hours and hours and lots of dollars on it. It has to be better than stock, so in my mind, it is and I will tell everyone about it. That my friends is human nature and if you are honest you either have done it or witnessed it from friends. Let's get on with it.

1. CAI
There are several Cold Air Intakes offered that will fit the 4Runner including the TRD intake. Do they work? Do they give you more power and efficiency? Depends on your definition frankly. Personally I think the only thing they give you is more or different noise. A member @TheWraith went above and beyond (good stuff) and actually did a dyno test of before and after a CAI. His numbers showed around 5-6 hp gain with a new CAI. I believe his numbers but unfortunately 5 of 270 is less than 2%. 2% is well within the margin of error of the machine. Changing air flow in front of a dyno by simply adding a fan in front of the vehicle can change dyno numbers by a lot more than that! I don't doubt his numbers and I know he truly wanted to do an "apples to apples" comparison. Unfortunately he had no other data to compare with. Why? Because nobody else has done it! Everyone depends on their "butt dynos" and we all know there is no butt the same. Wouldn't you think if we could improve hp and efficiency by 2% that Toyota would put that component in there from the factory? It's simple right? Moving on:

2. MAF Spacer
Basically this is moving a sensor in the intake and tricking the vehicle into thinking it is in a different running condition. Does it work? Probably. In certain areas of the throttle curve. How much hp does it add? Well, there is only testimonials and hearsay. Somebody (@quirt) did try to run a 4Runner on their dyno but they said they couldn't get it to work because of the shifting characteristics of the 4Runner. Now, @TheWraith got it to work so what's the story? Anyway, from looking at the data from other vehicles the 4Runner would probably gain, in certain acceleration modes, around 5 hp. Other times it would be no change and overall? Maybe 1-2 hp would be my guess.

3. High Octane Fuel
This one would probably work depending on your commitment. @harper7 has posted documentation from the Land Cruiser Prado that basically states that "over time, the vehicle will change timing due to the knock resistance of the fuel." I paraphrased that because I can't remember the exact words. Remember: Higher Octane fuel still has the same amount of energy as a lower octane fuel. The only thing it does is offer knock resistance. Also from what I remember it takes several thousand miles and several tanks of fuel to get this benefit. Not a tankful as many here have written. I have seen several documents that state an increase of 5 hp to 27 hp. Who really knows? Again, no proof other than testimony and butt dynos.

4. Exhaust Mods
Headers anyone? They will help. So will new exhaust. Unfortunately you have to delete cats and live with sensor problems. Also in many states you have to put your old exhaust back on every year for emissions testing as the new exhaust won't pass. How much will it help? Again, no data only hearsay.

5 and 6. Reducing weight and Driving Smarter
Out of all the mods listed above these two will help you the most. They can give you up to 4X improvement over a CAI!!! 10X improvement over the spacer! Unfortunately, they are no fun right? Actually driving like you have some sense, not installing big huge bumpers and skid plates to go to the mall. Using your roof rack for... nothing. Yep, that's no fun.
Seriously, you can have 20% efficiency gains by just driving smarter and reducing weight, much better than all the above put together.

Now I realize this is an enthusiast's forum and people get excited and are proud of what they do to their vehicles. They want to tell their buddies! They want to do build threads with only new mats and window tint! Great! Just keep in mind though that when it comes to performance mods there is very little we can do (without actually changing the long block) and the guys who are reading this might not know better and expect big things.
We didn't buy the 4Runner because it is powerful or efficient. If we would want that we would have bought something else. I read the posts in the CAI thread last night before they got deleted and members got banned. This is when I started writing. If you make a mod like a CAI or spacer or exhaust great, but don't try to convince everyone it is the best mod ever because in reality anyone can beat your mods by shedding a bit of weight and driving normal.

I'm sure this post will make me the most popular guy ever here at the 'ol 4Runner forum. I wrote this to hopefully shed some light on reality to some of our new members. If you have different results or actual hard data either proving or disproving the above please do not hesitate to post it. If all you have is the butt dyno data and "it feels faster" and "my mpg thingy said 2 mpg better" then post that somewhere else.
Greg

In my experience (with tuning German, Italian, and American performance cars), none of these mods will make a huge difference by itself.

Your engine is an air pump. The more air you can force in, consume (burn), and the more air you can force out the more power you can make. A cold air intake by itself won't do much. Your engine can't consume that extra air.

This is just one example.

Your best bet is to put your 4Runner on a dynamometer and measure the power output as it is. Get a baseline measurement and then add parts. Measure again. The numbers don't lie. Folks selling parts will tell you CAIs and exhausts will make tons and tons of horsepower, but they are usually wrong. They are in the business of selling parts.

The one difference I can tell objectively is using high octane fuel. My MPG went up using the same route day-to-day. We may have poor quality fuel here in the southern mid-west too.

Chris, great stuff but do you have proof? Did you document your fuel usage before and after and the mileage driven and fuel type? If you did then post it up. If not then unfortunately it's subjective to everyone but you.

I only have 3300 miles on my 4Runner, but I rarely, if ever, reset my MPG average on the OBC. Before, running 87, I saw 15.5 MPG. After switching for sh&ts and giggles to 93 I am now averaging 17.7 MPG (without resetting it). No over changes. Mind you, this is not driving the speed limit and with VERY heave tires installed.

I will eventually dyno my 4Runner as is as I would like to try a few tuners to lean it out.

I track my mpg in a spreadsheet. From 20 to 2000 miles I went from 17.2 to 18.8 mpg cumulative average on stock 87. From 2000 to 3400 miles on 87 octane I've continued to average 18.8. From 3400 to 11600 miles on 91 octane I've continued to average 18.8 mpg. YMMV

You see my point right? One guy, 3300 miles, no documentation other than your average mpg gauge. It would be great if you did run it on the dyno multiple times and documented your mileage and fuel type and usage. Then others would have something real to go on.

Exactly. Time could have something to do with that though. Different fuels at different times of year.

I would normally agree with you on the time thing, but I only have 4200 miles on it now. It's not my daily driver. Clearly, there's is an undocumented bump in ignition timing on high octane fuel, OR, our fuel here in my part of the country is crap.

but... but... nitrous!

I don't see any evidence to support a bump due to octane switching. I do plan to run 91 for a bit longer and then do 3 1/4 mile runs. Then switch to 87 and see if there is a measurable difference in the runs. I figure the engine will notice a decrease in octane due to knock sensors faster than fueling the other way around.

I do have a scanner I can use to check ignition timing. I will use that and post my results. My experience and gut tell me it does get bumped ever so slightly on higher octane fuel.

The "time" I was talking about is the time of year for mo mo. Winter versus summer gas. I do think there is a engine timing change but over a long period of time.

Make sure you do it in similar conditions (DA) too. Higher octane fuel is really only useful for forced induction engines. On properly tuned B8 S4's running a 104 Octane program (With proper fuel) usually nets 0.3 seconds in ET and ~3-4 MPH in the 1/4 over 91 Octane.

If you were able to have your 4 Runner tuned to take advantage of the fuel you may see some power increase.

APR was able to get +50hp and +57tq going from 91 Oct to 104 Oct on the revision to the S8 software, but thats in a whole other league.
APR Audi S8 4.0 TFSI V8 ECU Upgrade

The claim is 27 hp on premium on a 270 hp stock engine. 10% power should be easy to measure even with crude instruments.

This may fall into your CAI category, but just for the enjoyment of the interwebs.

Snorkel on not one but two 5th gens. Note: I have stopped tracking these metrics because the change was negligible after so long.

2013 T4R pre Snorkel 87 Oct. ~21000 miles on the clock 16.9 MPG (heavily modified)
2010 T4R Pre Snorkel 87 Oct ~89000 miles on the clock 16.4 MPG (heavily modified)

2013 T4R post Snorkel 87 Oct. ~29000 miles on the clock 15.3 MPG (heavily modified)
2010 T4R Post Snorkel 87 Oct ~94000 miles on the clock 14.7 MPG (heavily modified)

The number are from calculating acual fuel used and include driving (BOTH) vehicles to Colorado and NYC, as well as all city and off road driving. It is a few thousand miles of tracking and IMO a fair sample group.

Caveat: In CO both vehicles used 86 and 85 Octane fuels and all fuel used was summer blend. The lower Octane fuel was such a small percentage of sample I believe it to be inconsequential to the overall calculations.

My conclusion. the added air flow automatically made the ECM deliver more fuel, thus reducing my fuel mileage. Fact is, your ECM is far better at Stoichiometry than you are.

Note: It is worth mentioning, possible reason(s) for the difference in fuel mileage between two like vehicles. #1 The older vehicle has more Miles. #2 The Newer Truck has a TRD CAI.

As 1E stated, this is a hard topic to be "subjective" across the board. For instance, if you live at a different altitude and have a differently modified 5th gen.....you slap a snorkel on it, your numbers may be vastly different than mine.

I have customers that claim they have gotten 3mpg better after adding the snorkel.. I personally have records that tell a different story, but again as 1E eludes to...Human Nature....