Modifying the Stock Air Intake System

[goldstar]

Updated March 2010

For those of you who might have some interest in this area, this is about improving the OEM system by making three simple modifications, rather than replacing it with an aftermarket product. To begin with, I strongly suggest that you go to the website of that excellent Australian online magazine: www.autospeed.com
Click on Archived Articles and enter the title, 'Eliminating Negative Boost' in the Search function. This is a five-part article by Julian Edgar on improving a stock air intake system with air box. It is a great tutorial on improving the entire air intake system based on mods derived from measured results rather than guesswork.

Some time ago on the P-Club Forum, while doing a search on air intakes, I came across a post by Traveler titled "Restricted Intake Fix." Noting that the stock air inlet is in a sealed-off location allowing little room for outside air to enter, Traveler cut away the horizontal grill support right under the inlet to the snorkel, thereby exposing the inlet to direct air flow through the grill. He used a Dremel tool with a cutting disc but, not having one myself, I used an X-Acto knife with a cutting blade and a saw to remove the material. The plastic is relatively thin and you can score it and then cut it and snap it out. A bit of a pain but doable. I removed the entire piece except for a stiffening or support rib that connects the front and back of the grill together. This leaves a cut out area ~ 8.75" x 3.5".

Traveler reported that, "The engine now revs cleaner, harder and doesn't feel like it's choking off at 6000 rpm like it did before. It now pulls all the way to redline and my mileage went up by about 1.5 MPG." I obtained results similar to those reported by Traveler. There was a definite increase in throttle response and the engine revved-up more quickly and easily when going to WOT. Definitely more fun to drive. In addition, there was a noticeable increase in intake sound but nothing obtrusive-not at all like an AEM or Injen.

I assume the enhanced throttle response is due to the following factors:
1. The grill is located in a high pressure area.
2. Removal of the horizontal grill support allows the air flow a straight shot to the inlet with a possible ram effect produced by the forward motion of the vehicle.
3. This ram is converted to a slight positive pressure (or at least a reduction in negative boost) as explained in the cited article.
4. The intake air temperature will always be at the ambient-no chance of ingesting hot, underhood air.

Also to be considered is the fact that this is a relatively protected intake. As the air flows through the grill, it must then turn upward to reach the inlet. Since water is heavier than air, I presume much of the water would continue in a straight line or fall away from the inlet. I have, in fact, driven in severe rain storms and have never found that water ever entered the inlet in detectable amounts.

If you read Part 5 of the cited article you will see the dramatic reduction in negative boost the author was able to achieve by locating the air intake in a high pressure area. He was able to maintain atmospheric pressure in the system all the way up to the air box and, at anything less than full throttle, a measureable POSITIVE pressure. I am certainly not implying that I obtained comparable results from my mod. The point is to illustrate that locating the intake in a high pressure area can have beneficial results to a greater or lesser degree.

Below, photo of the engine bay illustrating the modified grill area:

[goldstar]

Removing the MAF Sensor Screen

This is the second intake system modification I performed. There has been much discussion on the forums about the function of the screen. Some maintain it is a protective device while others believe that it smooths out air flow (reduces turbulence) to enable the MAF sensor to provide a more accurate air density reading. My own research leads me to believe that the latter explanation is the correct one. Opinions also vary all over the map as to whether its removal reduces restriction in the intake.

For our purposes here, I want to focus on Part 4 of the cited article titled, 'The Airflow Meter'. The car in question is an Audi S4 2.2L 5-cyl Turbo. The FI aspect can be ignored because the following information pertains only to work done on the atmosphere side of the intake system. The intake system is similar to that of the Protege with an air inlet over the radiator leading to an air box. The MAF sensor is 75 mm (3") in diameter with a woven mesh wire screen on each side. Using a Dwyer Magnehelic Differential Pressure gauge (an instrument that measures very small increments of positive or negative pressure-read about it in the article), Edgar was able to take a pressure differential reading before and after the removal of the screens. Starting at 4000 RPM, an improvement was noticed after removal. At 6000 RPM, the maximum effect was recorded where the peak pressure DROP was reduced from 32 inches of water with the screens to 26 inches of water after removal. This represents a 19% reduction-a substantial amount. Look at the article to see % reductions at other RPMs.

The author feels that the, "Closely woven mesh causes a major flow restriction. This is not just because of the blockage factor of the wire itself, but because of turbulence which is generated as the air squeezes through the small openings." Edgar also believes that the function of the screen on the intake side is to protect the hot wire from damage if the air filter element fails. This article provides hard evidence that removing the screen benefits performance.

In reference to the hot wire MAF sensor, A. Bell states that removing the screen(s) cuts flow impediment and may give a 1.5 to 2% power improvement at maximum rpm.
Reference:
Four-Stroke Performance Tuning, Third Edition, by A. Graham Bell; Chapter 2, The Air Inlet System, page 26

Based on these results, I removed my MAF sensor screen. To access the screen, it's necessary to remove the MAF sensor housing. Loosen the clamp that holds it to the tube leading to the throttle body and disconnect it by pulling away the tube. Unplug the wire harness from the housing and remove the two bolts that hold it to the support bracket. Complete the removal by pulling away the other end of the housing from the air box. The screen is a light friction fit in the MAF housing. I used a wooden dowel as a drift and dislodged it with a couple of easy taps with my hammer against the drift. The whole job is fairly easy and only takes a few minutes. Be careful not to touch any internal parts in the sensor as a damaged sensor is very expensive to replace. Note that the screen (mesh) is directional should you ever want to reinstall it (for whatever reason). The side with the thinnest part of the grid is adjacent to the air box and on my screen is also marked with a spot of white paint. FYI, the inside diameter of the screen across its widest point, measured with my inside caliper, is ~ 58.25 mm.

Here are my impressions: Coupled with my first mod, an even faster throttle response and some added responsiveness during acceleration, particularly at higher RPMs, was evident. Additionally, some further increase in intake noise was noted. FWIW, I have run without the screen for ~ three years now with absolutely no problems or signs of damage or any hint of malfunction. No problems caused by potentially more turbulent, less laminar air flow through the MAF sensor, due to the screen removal, have been detected.

Incidently, for those of you who might want to take pressure measurements for research purposes, Dwyer Instruments is an American company located in Michigan City, IN and their website is at: www.dwyer-inst.com
Their Series 2000 gauges cost ~ US $60 and are available in various readouts including inches of water, PSI, Pascals and kiloPascals.

Below is a photo of the MAF sensor screen removed from my car viewed from the atmosphere side:

[THEGOLDPRO]

awesome write up, do you have any pics?? or can you get any??

[goldstar]

Sealing the Air Intake to Maximize Ram Effect

THEGOLDPRO,
Thank you very much. I have subsequently added photos.

This was the third and final, to date, intake system modification I performed. I had finally decided to take Julian Edgar's advice from the many articles he's written about this topic and seal off my air intake up to and including the air box to take advantage of any potential ram air benefits.

The snorkel has 4 drain holes located on its underside, the Helmholtz resonator and the air box each have one hole located at their lowest points. Initially, I had some concern that blocking these holes could lead to water ingestion problems but based on the experience of others and my belief that the intake as modified is a highly protected one, I concluded the risk was minimal. I am talking here of rainwater ingestion, of course, not running the car through standing water as high as the air intake.

As the mod was experimental at that point, I ruled out any permanent sealing method. I did not want to thread bolts into the existing holes as I did not want to enlarge them if I later decided to remove them. Also, I did not want bolts sticking into the air stream and possibly causing turbulence in the flow. My simple solution was to use duct tape-after all, sealing ducts is what duct tape lives for. The product I used was Nashua Tape Products, 11 mil thick, no.398 Industrial Grade, obtained from Home Depot. The tape is black so it blends in nicely with the duct components and satisfies the stealth factor. As it turned out, the tape became a permanent solution as it proved to be extremely tough and long-lasting and easily able to survive, long term, its hot. harsh environment. It took a licking and kept on sticking. Another way of looking at is that with all that wheeling, it kept on sealing.

The first step is to remove the snorkel. There are four drain holes on the underside of this piece. I cleaned the areas around the holes with 91% Isopropyl alcohol and then laid a double layer of tape across each of the holes.

The next step (snorkel still removed) is to remove the air box cover and remove the filter element. If you look down into the box, just below its air inlet, you will see the drain hole. Again, clean around the hole with alcohol and then cover with a piece of tape. It's a little difficult to seal the hole from the underside of the box because of lack of working room but it can be done. To make doubly sure that I obtained a good seal, I placed a second piece of tape INSIDE the box over the hole. Don't shudder, after many thousands of miles of driving the tape is still firmly in place and even if it did dislodge, it couldn't get past the filter.

Incidently, note that where the curved inlet tube joins the air box there is a very sharp edge where the air flow is forced to change direction. As an optional mod, you can smooth this area to promote better flow. I dragged an X-Acto knife blade backwards across the mold parting line several times to remove it and then I sanded the edge with medium grit (100) sandpaper until it was fairly smooth. A Dremel might be useful here But I didn't have one. I don't know how much benefit you'll get but every little bit helps - besides, it looks so much better now. If you do this, put some wet paper towels around the area to capture the plastic bits and make sure any debris is removed from the air box.

Finally, the Helmholtz resonator tube has to be sealed at its bottom end. This is rather difficult to do because of its location and lack of working room. At a later point, I ran the car up on ramps to check it out and it seemed to be sealing okay. This completes the mod and, after replacing the removed, you are ready to roll.

Results
In order to obtain a basis for comparison, before I did the mod I took the car out on I-287 and made several WOT acceleration runs from 60 to 95 MPH in both directions to get a feel for the cars performance in this range. I then went home, carried out the mod and returned to the same stretch of road for a retest. The temperature was in the mid 50s F throughout most of the day and therefore was probably not a factor. On the retest, both acceleration and throttle response seemed noticeably improved in the 60 to 95 MPH range.

I can now give a long term report on the consequences of running with a sealed intake. After running for ~ two years and many thousands of miles with this mod, I have experienced no problems of any kind. Even after driving through severe downpours during long periods of time, water ingestion does not occur and both the air box and filter remain dry. From time to time, I open the air box and remove the filter to see if any debris has collected in the bottom. The amount of debris collected is very small and I have never found stones or insects inside. There are no nicks or tears on the inlet side of the filter and no damage of any kind that I can find. The internal piece of tape inside the air box is also in like-new condition and shows no sign of lifting or pulling away from its position over the drain hole. As already mentioned, the duct tape has held up well and has not yet needed replacement.

I've previously mentioned the improvement in performance noted at higher speeds due to the enhanced ram effect provided by sealing. High speed passing on two-lane country roads is so much more fun and stimulating now. After living with the mod for awhile, I became aware that there also seemed to be an increase in performance at speeds below which ram effect should occur. I now believe that sealing the intake system has a secondary effect that may be as important as increasing ram. The snorkel sits over the radiator and adjacent to the exhaust manifold. Obviously, in an unsealed system, the four drain holes are perfectly positioned to ingest hot air into the intake. Since one of our goals is to supply only ambient temperature air to the engine for peak performance, any air ingested through the snorkel drain holes will serve to defeat that purpose.

I am suggesting that even if you don't want a sealed system, at least closing off the snorkel holes might be beneficial.

Conclusion
At this point, I'd like to recap all the mods I've done as described in this thread.
1. Removed horizontal grill support to expose air inlet to outside ambient temperature air and potential ram effect.
2. Removed MAF sensor screen to reduce negative pressure in the intake duct.
3. Smoothed part of the intake duct to improve air flow.
4. Sealed the intake duct between the air inlet and the air box to improve ram effect and to block hot, underhood air from entering the intake system through the drain holes.

Note that with the exception of the price of duct tape, should you elect to use it, total cost of the above mods is zero.

Happy Motoring!

[03MSP]

So, the only thing the little screen does is back up a failing air filter? If that's the case, I think I'm going to take mine off right now

[MP5_Racer]

Hum

[THEGOLDPRO]

now quick question, by removing this screen, doesn't it increase the risk of damaging the internals???? of the maf??? the screen is there to protect it right?

[Esquire]

The exact purpose of the screen was never determined.

Most believe it's there to protect the MAF in case of air filter failure, but if something enters your intake that is strong enough to rip through the air filter, you're going to have more problems than just the MAF. Specifically smaller pieces of debris that would be able to pass through the screen and enter your engine.

I took mine out about a year ago and noticed a slight inscrease in throttle response with my 1.8, and have had no problems at all. It's easy to find, just open up the intake near the MAF and look for the black plastic waffle.

[THEGOLDPRO]

i know where and what it is, but do you really think that mazda would spend money to put these in if it wasn't needed?? i mean im sure mits nothing major, but why risk it.

[goldstar]

THEGOLDPRO,
You make a valid point. However, this is how I view the problem.

First. I have run without my screen now for over one year without any problems, though by itself, that means nothing as I may have just been lucky.

Second. In making measurements of the screen, I can just fit a no. 18 wire gauge drill bit through any of the screen holes (the holes are actually square shaped). A no.18 wire gauge drill bit =.169" diameter or a little under 11/64". Therefore, even with the screen in place, stones or metallic particles of this size or under could pass through into the engine. Particles of this size could presumably cause engine damage.

Third. The only way particles can reach the MAF screen would be for a catastrophic failure to occur in the air filter element such as a tear or a hole. I consider such a failure to be highly unlikely although I realize that this is just an assumption. Based on my belief, I feel the screen removal is a safe proceedure. I guess, in the end, it comes down to how much we're willing to gamble on our beliefs.

02 DX Millenium Red

[Esquire]

What goldstar said is what I was trying to get across. The holes in the piece are about 3/16 inch (~.5 cm) in width and height. Debris that can fit through that hole could almost do more damage than debris that couldn't. Small debris would be more likely to be carried by the air and could also slip through the valve clearance (though I don't know exact measurements), thus completely screwing over your engine.

To me, the shield isn't much of a safety feature, so I decided the very slight risk was worth the performance boost (albeit also very slight).

[glyph]

I will take a look at my own filter setup, and get some pics posted. I am VERY interested in doing this to my own, and if I do, I will post a HOW-TO.

goldstar, thanks for posting all this. great help!

[goldstar]

glyph,

That would be good if you can post photos. It will certainly make things a lot clearer for anyone who might want to do these mods. I'm glad you found the post helpful.

02 DX Millenium Red

[kickniteasy]

Quick q, would doing any of this void my warranty........I'm paranoid.

[goldstar]

kickniteasy,
I'm sure that Mazda would consider that you had voided your warranty if you remove the MAF sensor screen and some kind of traceable damage results. However, as I stated earlier, I believe the chance of something like that happening to be extremely remote.

As far as removing the horizontal grill support is concerned, I don't see how this proceedure could cause any kind of conceivable damage short of driving through a wall of water nearly as high as the hood itself. With the inlet exposed to ram air, dust particles might strike the air filter with greater force but I can't see the filter being holed as a result. I don't believe water ingestion would be a problem as I explained earlier.

In the last analysis, I guess almost any performance modification can carry some risk. We have to weigh the risk vs. the benefit obtained and decide which is more important.

02 DX Millenium Red