As for many types of cars, along with Toyota Tacoma's, the stock air intake is not large enough to allow maximum performance. Specifically, in my Tacoma, there was one small 90 degree elbow that came off the side of the airbox that led to the inside of the right fender. This was quite restrictive in air flow terms, so with one simple modification called the "Deckplate Mod," the airbox was allowed quite a bit more air and still retained full filtration capabilities.
Overall, this mod gives the Tacoma engine about 7 more horsepower shown by dyno tests. The engine sound will barely change, except while downshifting or accelerating fast. Around 3,000 rpm's, the engine starts to roar. The sound is great, but by no means over-bearing.
This pictures shows the truck with its airbox removed. Three bolts must be taken out along with the connection for the (MAS) Mass Air Sensor. It may also be a good idea to remove the mass air sensor itself because in later steps you have a chance of getting plastic in it or breaking the unit while working on the box. These units can cost hundreds of dollars, and it only needs two bolts taken out to be removed.
This is a picture of the elbow that leads into the fender. As you can see, it's not a big enough opening for full engine performance when it's needed.
This is a picture of my airbox taken out of the vehicle. It stands upright in the vehicle just as shown, and two clips are removed at the top to slide out the air filter. After the air filter is out, I also removed the small 15 AMP EFI fuse located in the fuse box. Everything is labeled fairly well so it's not hard to figure out. This will reset the computer setting for the new changes and readjust your shifting patterns so they are correct.
Here are the supplies you will need. The total cost is around $15, probably the cheapest engine upgrade you can find. What you see here is a 4" deckplate, which can be found at just about any boating/marine place. I got mine at Pamp's Outboard. I did not find these at places like Fleet Farm or Home Depot. Then I also got 6 #8 pan head screws, used to screw on the deckplate. Also a tube of silicone was used, which makes the seal air/water tight. It's best to find the "sensor safe" kind so then you don't have a chance of messing up you MAS, but if you let dry and air it out, you should be fine just like I was.
First you unscrew the deckplate. Next use the outer ring and trace a line around it. Your cut will have to be slightly bigger than the ring itself so it fits properly. I put the deckplate off-center to the left of my box, to avoid the windshield washer fluid container getting in the way.
Here is a picture after I cut the hole out. I used a portable jigsaw. A dremmel would also be a good choice, but I think this would have worked better because of the tough saw. The other side is waffled, so much thicker plastic needs to be cut. I did have to slightly re-cut to give it a better circle shape since I couldn't see my lines half the time, and then proceeded to shave around the complete circle so I would have a nice, clean fit.
Here is the ring fitted in the box. After you fit it, drill the screw holes using a pretty small bit using the ring as a guide.
After you have your holes for the screws drilled, place a line of silicone around the ring. I used about 2 circles around. Then line up the holes and place the ring in its place. Push down firmly and then screw in the screws.
Here is a picture with the center screwed in, for a complete air/water seal. The reason for having this center piece is if you choose to go muddin', or your going to be traveling in lots of water or on very sandy back-roads, you can screw it in and don't have to worry about getting dirt in your filter or water in the engine. The center part should not have to be put in for any type of rain.
Here is the airbox installed back into the truck. I then connected the sensor wires, screwed in the three bolts, and replaced the EFI sensor in the fuse box.
Another picture with the center piece of the deckplate in place.
It takes approximately 200 miles for the Tacoma to fully reset the computer. Shifting can be a little funny at first, but it all will correct itself.
Overall, from a stop to start you can feel a bit more "throw-back-in-your-seat" feeling along with accelerating between 25-45 mph.
For $15 and a gain on horsepower, you can't go wrong. This mod spread like wild fire among Tacoma owners and many have done it. If you don't want to waste lots of money on special K&N filters/intakes, and have an hour of free time, I recommend this modification.