Toyota 4Runner Topsites

  Air Induction



There are many products on the market that "claim" an increase in performance "up to 15 bolt on horse power." Well that is saying from 0 to 15 HP increase, or maybe just zero, or worst, less then zero. I tested several different configurations in my air induction system. Some of the results were expected and some were not. I have laid out my tests and the results so read on.

These tests were conducted with my 96 4Runner equipped with, TRD Supercharger with the FMU, Edlebrock Headers, Borla Cat-back exhaust, Kenne-Bell Boost-A-Pump, and the stock MAF unless other wise indicated.

I do not recommend that you make any mods to your air induction system if you have a supercharger unless you increase fuel delivery. This includes removing the elbow. Some others have made these mods without increasing their fuel delivery and lost power. I believe this is due to the lean fuel mixture with the stock fuel system and these mods just compound the problem. If you have a supercharger at a minimum you really need to install a BAP and a properly functioning FMU. See my fuel delivery page for more information.

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K&N and AMSOIL drop in air filter:

One of the first modifications I did was to install the free K&N air filter that came with my Borla Cat-Back Exhaust system. I ordered it from Performance Products and they included a drop in K&N air filter. I did not notice any increase in performance with the K&N filter and later dumped it when I found that it does not do a very good job of filtering air.

I had seen some other test results showing that the oiled foam filter from AMSOIL worked better then K&N. These tests also showed that the K&N let too much dirt through. That kind of makes sense. If you hold the K&N up to a light you can see little holes in it, and even K&N says the dirtier it gets the better it filters. I guess the added dirt plugs all the little holes.

I got my AMSOIL filter (TS-115) and found it to be very thick and it completely blocks all the light. I thought that maybe in some applications the AMSOIL might beat K&N on HP, but this may not be one of them.

I ran a comparison of the K&N and the AMSOIL on the dyno and was surprised to find that the AMSOIL beat the K&N. I did not expect it. I have no doubt that the AMSOIL was a better air filter for filtering out dirt, but I was surprised it also made more power.

This test used the standard configuration and the VPC with 270 cc injectors.

Here is another dyno run I did with the Split Second with the 3 inch MAF and 305 cc injectors. As you can see the AMSOIL air filter made more power then the drop in K&N again. That is two different comparison tests on two different dyno dates with different configurations. So for those of you that have your minds made up and do not want to be confused with the facts just keep your heads in the sand and ignore the hard data.

You will notice the difference in the first gear run. That was caused by excessive wheel spin and the tires breaking traction again during the shift with a loud CHIRP. It was a real attention getter around the dyno shop.

If you want to get an AMSOIL air filter for your truck and  have a 96+ 3.4L 4Runner or Tacoma you want the TS-115 if you have a 2.7 you want the TS-117. After writing down the numbers go to my AMSOIL web page.  I have the links you need to order the filters and what every else you want on line.

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Modified Air Box:

When I changed the air filter I took a close look at the air box and tried to figure a way to modify it to increase airflow to the engine without increasing the induction noise.

I got to work with my trusty Dremel tool and cut open the front of the air box. I left a good size lip around the edge of the opening to act as a sound baffle to reflect the inductive pulse back down the air tube into the engine and to maintain structural integrity of the box. My work paid off and I noticed an increase in performance without an increase in induction noise.

Franken Taco has taken my open front idea and improved on it. He cut a whole in the front and then installed a boat deck plate in the opening. The deck plate has a center plate that can be removed for normal operations and then closed for water crossings. This seems to have become the standard airbox mod for the "off roaders." Check out his web page for more information on this good improvement on my idea.

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K&N Fuel Injection Performance Kit:

K&N released the Fuel Injection Performance Kit (FIPK) for the 3.4 and I ordered one from Performance Products. By this time I had the supercharger installed. I was surprised at the substantial increase in induction noise and I did not notice any increase in power.

I was told by the people at TRD that they have tested the FIPK and they saw a reduction in power. I later ran my own dyno test and found this to in fact be true. You do have to admit, it does look faster, right??

The FIPK also cause damage to my 4Runner. The overall design of it does not allow enough give to allow for the movement of the engine in its mounts. The FIPK uses the same mounting points as the stock air box and I found that the FIPK had pulled the mounting bolt right through the fender mounting point, ripping and tearing the sheet metal. I do not recommend anyone install this set up in his or her vehicle. I had a reduction in power with my supercharger, and damage to my 4Runner as a result of installing the FIPK. I reinstalled my modified air box.

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Remove the Elbow:

I was contacted by TRD and we discussed the dyno testing that I was doing and my air box modifications. I was told about removing the "elbow" from the air box and that they saw and increase in performance in doing so. They asked me to test it on my next set of dyno runs.

The elbow is mounted in the inner fender wall and the pipe from the air box slips into it. On the other side of the fender wall the elbow makes a sharp right turn and joins another tube that continues backward and upward inside the fender. The sharp turn is very restrictive.

It is easy to remove. Remove the air box and unbolt two bolts that hold the elbow to the fender. Then wiggle it out.

I did get a suggestion from one of the visitor to my site. He recommended removing the elbow and then cutting off the part that is inside of the fender and then reinstalling the remaining part to maintain the seal with the fender wall.

Here is a link to a web page that a friend put together that lays out the elbow removal really well.

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The Test Results:

During this set of dyno testing I compared all different configurations with the air box. I seal the opening I cut in the front of the air box and ran it. I then removed the "elbow" and ran it. Then I removed the temporary cover sealing the hole I cut in the front of the box and ran it. I then remove the air box and tested the FIPK.

Configuration and Results: *Note- runs with the stock air-box used a replacement drop in K&N filter and the stock AFM*





Run 9 Stock Box No Front 173.3 HP 205.5 HP 210.8 HP
Run 8 Stock Box No Elbow 170.7 HP 205.1 HP 210.8 HP
Run 7 Stock Box 168.8 HP 199.5 HP 201.8 HP

My results showed that opening the front of the air box made the most power, followed extremely close by just removing the elbow. These two configurations and the completely stock box beat the FIPK.

Configuration & Results:*Note- runs with the stock air-box used a replacement drop in K&N filter and the stock AFM*





Run 9 Stock Box No Front 173.3 HP 205.5 HP 208.6 HP
Run 7 Stock Box 168.8 HP 199.5 HP 202.2 HP
Run 6 K&N FIPK 169.4 HP 202.3 HP 199.0 HP

This is the test that is sure to get some folks upset. Performance products is selling the K&N FIPK for $219. The K&N FIPK beats the stock box by .6 HP in 1st, 2.8 in 2nd, but looses to the stock box by 3.2 in 3rd for an average loss of .06 HP.

Now if you just cut open the front of the box you get 6.4 HP over the stock box for free or 9.6 over the K&N FIPK. Remember from the previous chart you will get basically the same results by removing the elbow as cutting open the box. I think this might be the way to go so you can pop it back in if you decide to go swimming.

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Other Ideas:

There are a couple of people that have taken their induction systems a little further then I have.

Ron has installed custom scoops that fit below the head lights.


Travis has installed custom fiberglass hood and front fenders. He is working on custom fiberglass rear bed sides. Email Travis for more information.

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Final Recommendations:

My final recommendation for the air filter and air box is to use an AMSOIL filter and remove the elbow from the fender wall. You can always pop the elbow back in when needed. The next step is to remove or replace the air flow meter. I cover that in the fuel delivery section.

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