Headlight Switch Options

Pros: Easy to Customize and Install, Doesn’t cost very much
Cons:
Cost: Varies from $6.40 to $16.60

For most, the stock headlight switch has a black cap (61-31-8-400-003) on top of a black sleeve (61-31-8-389-547). Some Z3 were ordered with a chrome package installed at the factory and might have a different all chrome switch but this is how the majority of Z3s rolled off the assembly line between 1995 an 1999. The cap simply snaps onto the sleeve, the sleeve is screwed on and held in place with an 8mm nut. Both can be replaced in a couple minutes.

If you just wanted to replace the cap you could order BMW part number (61-31-8-400-004) which is an all chrome cap. This is a very eye catching combination but some think that the all chrome cap is a little too eye catching. The chrome cap lists for $6.83 and it simply snaps on in place of the black cap. Be careful snapping the new cap in place, there are three pins that line up into some slots so make sure those line up before trying to snap on the cap.

If you wanted something a little less flashy, BMW also offers a chrome trimmed black cap. BMW part number (61-31-2-694-602) lists for $10.20 and it also just snaps on in place of the black cap. This cap is trimmed in chrome with the face remaining flat black. This is the same cap that is now standard on the model year 2000 M roadsters.

If you are wanting even more chrome, the sleeve behind the snap on cap also comes in a chrome version. BMW part number (61-31-8-389-880) lists for $6.40 and once the cap is removed a single 8mm nut can be seen that holds the sleeve in place. The sleeve also has metal threads so once the nut is removed the sleeve has to be unscrewed and replaced.

Z3s that were ordered from the factory with the chrome package received a chrome cap (61-31-8-400-004) on a chrome sleeve (61-31-8-389-880). The total list cost of the two parts is $13.23

What I choose to install in my M roadster is the combination of a black chrome trimmed cap (61-31-2-694-602) on the chrome sleeve (61-31-8-389-880). The total list cost of the two parts is $16.60 and it blends well with my ever growing chrome collection.

Not pictured, but also available is an Aluminum cap (61-31-8-401-196) and an Aluminum sleeve (61-31-8-401-270). These were offered as part of an Aluminum package on the now discontinued 2.8 coupe.

Chrome Lock Pulls

Pros: Looks Good, Inexpensive, Easy To Install
Cons: Lock Pulls Stick Out Slightly Further
Cost: $9.36 (list)

Click for Larger ViewHere is another simple and inexpensive upgrade for chrome lovers. The stock Z3 lock pulls are black, but BMW makes it easy for you to change to chrome lock pulls. The picture below is BMW part 51-21-8-399-241 which lists for $4.68. Technically there are left and right versions of this part (51-21-8-399-241 & 51-21-8-399-242). When there is a left and right item the odd part number is the “left” item assuming you are seated in the drivers seat. But for our use you can order 2 lefts, 2 rights or one of each because we’re going to only use the chrome cap on top of each operating rod.

Click for Larger View

Click for Larger ViewRather than take the door apart to replace the entire operating rod, if you pull up on the lock pull and keep twisting it around it will eventually come loose and you can pull the plastic lock pull cover off the operating rod. Do this on the new parts you just purchased and on the stock (black) lock pulls. Then place the chrome lock pull on the stock operating rod and twist it back down. These parts really are not designed to be screwed on and off but they are plastic and can be replaced in this manner.

Update: I have received several email questions regarding this removal. Yes it is difficult, the plastic is held in place with a bump on the operating rod. Twisting and pulling is what worked for me, just be careful not to damage the finish on the plastic part.

Click for Larger ViewIt may be easier to do this with the doors open. When the doors are open the central locking system will not allow the lock pull to be depressed. With the lock pulls held in place by the central locking system, and using the twist and push method I replaced both sides rather quickly. It is much easier to do it this way rather than take the door apart and replace the entire operating rod.

Chrome Hand Brake Button

Pros: Looks Good, Inexpensive, Easy to Install
Cons: Only For Chrome Lovers
Cost: $3.10 (list)

Here’s a real easy upgrade, that doesn’t cost much, and looks good. Change the black hand brake button to chrome. BMW makes a chrome hand brake button part number 34-41-1-163-199 that lists for $3.10. I’ve added several chrome accessories to my black and gray interior and this small inexpensive upgrade adds to the look.

The button just screws onto the hand brake. To remove the old button simple unscrew it. It takes a lot of turns but you should be able to notice it slowly coming free of the hand brake. Once the old one is unscrewed simple screw the new chrome button on in its place.

Z Rated Tire Patch-Plug

Z Rated Patch/PlugNot soon after recovering from the expense of new M roadster tires I discover a nail embedded in the tread. I immediatly remembered previous debates of patching vs plugging damaged tires. Both solutions appeared to work but in either case you technically lost the Z rating on the tires. If you’ve got a lead foot this loss of rating can be concerning to say the least.

When I brought my problem and concern to the attention of a tire repair shop, I was happy to find a solution. Pictured to the right is a Z Rated Patch-Plug. I have no idea who makes it or any other details, but the tire shop made it sound like a fairly common item they use whenever repairing a Z rated tire.

The tire tech broke down the tire and removed the nail. The patch-plug and area around the hole inside the tire were cleaned and then coated with what I assume to be a thick glue substance. The pointy end of this patch-plug is threaded through the hole the nail left, until the patch (round part at the bottom of the picture) makes contact with the inside of the tire. You end up with what appears to be a nail sticking out of your tire. The tire tech snipped off the protruding section, put the tire back together and then rebalanced it. I was told to take it easy on the tire for a day and then consider the tire “good as new”.

Note: I did not ask permission to publish the name of the tire repair shop. Previous experience in publishing information on ///MZ3.Net has taught me to error on the side of caution, so the actual name is withheld but your local BMW dealership should be able to repair the tire or find someone who can.

Update: It’s been three months and the tire has preformed well. While I don’t want to incriminate myself, lets just say that I have full confidence in the Z Rating of the patch/plug 🙂

Reader’s Comment: Good article on correctly repairing your tire. The repair you used is the only one that is recognized by the major tire manufacturers. It is made in Johnstown, Ohio by Tech International. You’ve probably seen the red Tech logo in lots of tire stores, gas stations, etc. Their web site is www.techtirerepairs.com They don’t sell to the general public and as you noted, this particular repair takes some skill and equipment to install.

HMS Window Blanket for BMW Convertibles

Pros: Provides additional protection for the delicate and expensive rear plastic window.
Cons: Harder to fold and store because of the bulkier design
Cost: 39.95

BMW created a device we owners quickly named the “window blanket”, it was a simple yet functional blanket that draped across the rear window and protected the window from scratches when the top was folded down. But the one thing the BMW blanket didn’t do was stop the window from creasing when the rear window folded incorrectly (with a wrinkle). HMS improved the BMW design and took it one step further by adding a bulky area to middle of the blanket which makes the window fold in a more rounded way in order to keep the window from creasing. It also appears HMS used a heavier fabric so there is some additional padding associated for the entire area that the blanket covers.

The bulky area appears to be filled with beans or something similar. The added weight from this bulky area forces the top to fold correctly and keeps it from folding to sharply (which can cause creasing). The improved design works better than the original design in protecting the top from these creases but there are some trade-offs. The HMS design is harder to fold and store because of the extra padding. The padded area is divided into three sections so folding it width wise is limited to three three sections. With the original BMW blanket I kept it tightly folded up and stored in one of the pockets of the trunk organizer. However with the bulkier HMS design this was no longer possible. I end up rolling it lengthwise and laying it in the area behind the center console. This might actually be a better location since it helps remind me to use the blanket when I want to put the top down.

I’m trying to get in the habit of using the boot cover and HMS blanket more often since I was starting to see some wear and tear on the plastic window. For this reason I like the HMS blanket more so than the BMW blanket. It keeps the top folded correctly and provides additional protection for the delicate and expensive rear plastic window.

Sold By:

HMS Motorsport

www.hms-motorsport.com

(888) HMS-3BMW

Laguna Seca

The Night Before – Preparation time! I checked and topped off all fluids and set the tires to slightly over track psi because there is not air at the track… it is better to have too much then to little. You will adjust these at the track. If you have been running on the same air filter and oil filter for a while you might want to swap these out. Make sure to bring water and possibly some bananas. Tracking is a very tiring de-hydrating exercise and the getting a leg cramp at the wrong time can be fatal! Luckily a friend warned me of this. Unfortunately I wasn’t warned about the need to bring tools. The tech session described below outlines this problem. Don’t forget the helmet and get lots of sleep.

5:30am Alarm – Ouch! I woke up, drove from beautiful scenic Salinas to Laguna Seca. On the way to the track, I filled up the tank of gas. Don’t forget to do this, because track gas, if available at all, is very very expensive! You will use a full tank at an all day track event.

Doug Peete7:00am Laguna Seca Racing Paddock For Tech Session – Here the cars were checked to make sure they are in good working order. Being a guest of the Miata club made things a bit difficult because they didn’t have the tools required to inspect my car. My recommendation to guests at other car make’s events is to make sure you bring a full set of the appropriate sockets and wrenches, a torque wrench and any manuals required to prove you are using the proper torque settings. Also make sure that all of your car’s fluids are at the proper level (don’t overfill) and are not leaking.

Foggy MThe tech session was also a good time to size up the other cars at the event. I would guess that we had nearly 50 cars at the event. While every form of Miata from stock to supercharged was well represented there were also a few other “oddballs”. Namely we had: a vintage Shelby 350, an early ’90’s Mustang 5.0, a C4 Corvette, three Porsche Boxsters, three Honda S2000s, an e36 M3, an e34 M5 and a Ferrari 355. Woohooo! It is very neat watching and listening to the other cars turn laps.

* Some tips for the beginners at their first track event: Remove the floormats and any loose items from the cockpit. I ditched all of the items in the glovebox, the items in the cargo net, the items in my Leatherz armrest, the mobility kit in the trunk and all of the tools.

* The side windows were required by the track to be down. I also found I preferred the top down and I used the tonneau cover to make sure any “agricultural excursions” didn’t result in a dirty liner.

* Ear plugs are highly recommended (yes, in addition to the helmet) as the wind noise will scare you into driving slower due to the perceived speed from the wind noise. Don’t worry, you can hear the engine, brakes and tires just fine with the ear plugs and the helmet.

* Get the tires to the right pressure. I had the tires at 34 psi from the night before and dropped them to 32 psi at the track. Street use for my setup is 30 psi.

* Dig into a banana and water… it is never too early to start hydrating.

8:00am Class – Class consisted mostly of describing proper track etiquette (hand signals for passing and indicating a lowering of speed as well as thanking the corner workers), the flag system in use for our event (my head hurt from cramming in all of the flag meanings) and a short introduction to the instructors. We also were divided up into three groups ranging from first timers (me) in Group C to the old pros in Group A. The entire day was divided into 20-minute sessions that rotated the Group which was on the track.

* To sum up a few points: Our Flag System (Not the definitive flag system!!!):

o Green – go,go,go

o Standing Yellow – proceed with caution & no passing

o Waving Yellow – danger ahead, proceed with caution & no passing

o Blue with Yellow Stripe – passing is okay

o Red and Yellow Stripes – surface problem on track, slow to a stop and await instructions from track worker

o Red – some sort of major problem, slow to a stop and await instruction

o Black – you did a “no-no”, proceed to the pits for a talking to

o Checkered – final lap, no passing cool down lap

* Always give some waves or thumbs up to the corner workers on the final lap. They spend all day in their boring towers keeping your butt safe, so thank them on your cool down lap!

The Starting Grid

9:00am First Lap – The first session is a very slow “follow the instructor lap”. Speeds are kept to under 50mph. The main goal is to learn the proper lines to take on the track. In 20 minutes we were able to get several laps around the track. Tip: In the starting grid try to get as close to an instructor as possible. Remember the “telephone game” where a large group gets into a circle and someone in the circle whispers a message to the person next to them and that person passes the message to the person next to them and so on until the message returns to the recipient. The message never is the same when it returns to the first person… such is the follow the instructor game – the car behind the instructor takes a slightly sloppier line, the next car is sloppier and the next is sloppier still.

Also, the speeds on the first lap are very slow. At slow speeds the lines demonstrated by the instructor don’t make sense and seem exaggerated – they aren’t! At this point the best thing you can do is turn on your mental tape recorder and record the lines… you will be happy later on when you are at speed and the lines begin to make sense. Not following these lines will result in an “agricultural excursion” for you and your car.

The track initially seems docile until the back set of laps starting with a left turn resulting a quick elevation change up, a flat tight ess turn followed three-story plummet of an ess turn known as the Corkscrew. I never knew that racing consisted of elevation changes as well as the usual left/right turns. Driving along on the flat ess and then watching the road literally disappear from sight is an unnerving feeling!

* Some tips for the beginners at their first track event: Never ever set your parking brake following a session. This can cause warped rotors.

* Always give the car a cool down run after the session. I usually took my checkered flag lap at 8/10ths except for 1 or 2 of the turns which I really wanted to work on and then would follow my lap with a slow run around the parking lot inside the track to get the engine and brake temps down.

* Have some more water and chant the following mantra “I will not cramp, I will not cramp…”

9:40am My First Session In An Instructor Car – Ace driver and tuner, Rick Weldon of PR Motorsports – Hayward gave me a ride inside his race-prepped Miata. The car was an early model Miata stripped of many of the interior parts, outfitted with a tuned suspension, a tuned intake and exhaust and ready to roll at just over 2500 pounds and 140hp. A reasonable power-to-weight ratio, but the beauty was watching Rick drive. While there wasn’t any lap timing going on, it was easy to see that Rick’s performance was several seconds faster than ANY CAR on the track… high performance German and Italian metal included. The old adage that the first nut that needs to be tightened is the one behind the wheel is very true. It was hard to notice actual speeds during the white knuckle ride, but Rick was easily able to pile at least another 5 mph on top of my speeds through the Corkscrew!

It was amazing to be in the car with Rick as he told me how to approach each section of track. Again my brain recorder clicked into the Record Mode so that I could attach his sound bytes to my track visuals I was also mentally recorded. Throughout the rest of the day I replayed Rick’s words over and over to encourage myself to find the same smooth flow that Rick showed me on the track. Rick also provided me with one really neat experience… the final lap of our session he told me to narrate the flow of the lap as he had been doing throughout the previous laps. This really helped cement all of his words permanently into my mind. I am not sure if this is a standard instructor tip, but it was an awesome way to prep me for my next lap. Thank you Rick! Tip: Get an instructor ride ASAP so you can feel the right flow around the track! Just following the line in the first lap didn’t give me the insight in to the track that the ride-along gave me.

10:00am My Second Session – No instructor this time. This session was mostly a get acquainted with the track driving session. My laps were slow as I learned the lines and learned how to get a good “scan” (Rick’s vocabulary) of each section. Proper setting up of a turn starts with looking through the turn, then scanning the corner workers for flags, scanning for other cars, and then sighting through the turn again. The scan took some practice to perform initially but quickly became routine and can keep you out of trouble by respecting the corner worker’s flags.

The Starting Grid

10:40am Rick Drives The ///M – Wow! Rick took the wheel of my car and gave me a ride as the instructor of one of the advanced sessions. It was incredible to feel what the car is capable of in the proper hands. Rick seemed very impressed with the capabilities of the car saying that it is a really solid and balanced vehicle. The current limits of the car were more based on the stock pads (he experienced a bit of fade) and tires (he drives DOT approved racing tires on his Miata) and not mechanical. It looks like I know what my next upgrades will be!

11:20am My Third Session – I finally started to get a better feel for the track and was able to begin picking up speed. It was during this session where I began pushing the car into some drifts around turn 2 and turn 3. Despite the Stage I Dinan suspension, I could still feel the car tending to understeer in the drift, causing me to drift farther to the outside of the turns than I wanted (am I just rationalizing the adjustable roll bars in addition to the new pads and tires Rick recommended? Nah!)

On a related note, the engine in this ///M pulls just as bly as any car in the straight aways. On this lap I spent time with both the GT350 and the Ferrari and neither was able to pull an inch on the ///M. Also when I came off the track, several people commented on the exhaust note the car generated. “Your car is the coolest sounding car on the track!!!” Very cool indeed. Apparently the GT350 was louder, but the Dinan Cold Air Intake made an insane growl for the spectators standing in the pits. All this despite UPS losing my Supersprint (yes, it currently is lost… it scanned into Oakland Airport and never made it out), so I was running the stock pipes. I need to get a video camera so I can tape this next time. Anyway, whether the Dinan Stage II chip/Cold Air Intake make any horsepower is mute when these products make the car sound better then the Porsches and Ferraris with which you share the track.

Straightaway1:00pm My Fourth Session – Following lunch, we get our fourth session. Basically things start coming together on this lap. My times were consistently faster and I start learning how to four-wheel drift in turns. Just as I am starting to feel good about my experience an e34 M5 passes me with a 3 passengers in the car. Luckily it was an instructor driving, so I don’t feel too bad, I think an instructor could pass me with a bicycle! Another good reinforcement that it is the driver and not the car that makes for good laps.

My increased speeds and harder breaking really begin to heat up the stock pads. I began to feel a bit of fade towards the end of my laps. In order to avoid the infamous brake rotor warping, I take my checkered flag laps at a slightly lower pace, so the car can breathe. And hey, it is easier to wave “thank you” to the flag workers this way. Also, I drove the car for a slow victory lap around the inner-parking lot following the last lap to further blow cold air onto the brake rotors and the engine.

2:00pm My Fifth Session – The session was late because the Mustang drops some radiator fluid onto turn 3 which promptly sent an M3 and a Boxster into a spin… luckily into runoff areas without any damage. This was a great reminder that even a perfect driver can and will eventually find themselves venturing off the track. Tracking is full of random occurrences and about the only sure thing is that something strange will happen. Pay attention to flag workers and remember how difficult it is to explain to your “significant other” over the telephone that half of the car is in turn 2 and the other half is in turn 3.

After the track was cleaned (I didn’t see how) we began our fifth session. I couldn’t see any remnants of the cleanup, but we were kept under a standing yellow flag for the first two laps. This was a good time to cruise the track reminding myself of the proper line without worrying about speed and other cars. The next laps were some of my best yet, but still far from the laps Rick had in the ///M. Rick offered to sit in with me for a few laps so I pulled in and took him up on the offer. He was able to quickly identify new areas for me to concentrate on and corrected several bad habits. I should have taken him up on the offer sooner in the day since there was only one last track session for me to apply his recommendations to. The specific advice I received is moot… the instructor will give you the advice you need. Make sure you get an instructor to ride with you at least twice in the day (once in the morning to talk you through the track and then once late in the day so they can correct any bad habits picked up throughout the day.

2:35pm The Witching Hour – Late afternoon at track events is commonly called the witching hour. People are tired from running hard all day and are a little too comfortable with the track for their own good. One of the Miata’s in the Group A class (the top class) pushes it too hard in turn 2 and ends up bending a tie-rod. Apparently something always happens during the witching hours, so don’t let it be you. If you find yourself going through the motions, check yourself. Maybe it is a good time to pull into the pits and get some water and a banana!

2:50pm The Last Session – Best laps of the day by far… I even finally got a good line through the backside including the Corkscrew and turn 9, a weird off-camber turn that looks easy but somehow is quite challenging.

3:15pm The Day Is Over – Time to drive back to the East Bay. What a day!

Turn 3

1.9 ROAR “RAM-AIR” Intake

Pros: Improve sound and performance, carbon fiber components and shield to hinder recirculating hot air intake
Cons: Vague installation instructions, intake system enclosed in engine compartment
Cost: $348

Despite the discontinued sales of the 1.9 Z3 in the US, there are many 1.9 owners who want added performance and most of all who still love their cars. With this in mind, there has been a slow start of third party manufacturers that offer upgrades and modification(s) to these loved but not forgotten Z3s.

Presently, there are a few manufacturers who offer an ‘air-intake’ solution to the 1.9 Z3. According to a previous article on the MZ3.NET, the K&N filter charger has some inconsistent performance results. THe K&N filter charger successfully addressed the restrictions in the stock intake allowing more volume of air to enter the engine. However the flaw with the K&N filer charger system was that the source of intake air was the (hot) air trapped under the hood of the Z3. While the intake was allowing more air volume to enter the 1.9 engine, the actual air mass varied greatly depending on the air temperature under the hood. Because of this flaw it was actually possible to loose engine power. (In case you haven’t caught on, cold air has more mass than hot air). Because of this, many Z3’ers (especially those living in hotter climates) avoid in installing such a design in their vehicles.

Since I received the DINAN UPGRADE for my 7/97 build 1.9, there has been no answer as of yet for the release of the DINAN COLD AIR INTAKE SYSTEM for the 1.9 since its debut for the 6 cylinder Z3s. Because of this I wanted to see if there are any third party companies that offer such a system for the 1.9 besides the K&N filter charger. I came across a company called “ROAR” (www.roarfilter.com) that offers such a system for most BMWs including the 1.9 Z3. Though fairly new to the name I decided to call and investigate what this company offers and stands for: I called the company and left a voice mail message with them explaining my interest in their air-intake system for my 1.9 Z3. Two days later I received a call back and spoke to a very nice and enthusiastic sales manager of Roar named Scott. He was very friendly and excited to explain to me how their air-intake system functioned and how it was designed. He welcomed the challenge of putting the ROAR air-intake system against any other system designed for the BMW Z3.

The ROAR intake system is similar to the K&N filter charger system in that it addresses the air flow restriction of stock BMW airbox. Where the ROAR system differs is that it also addresses the problem of air intake temperature, by providing a carbon fiber shield that helps reduce the engine’s intake of hot air from inside the engine compartment. The construction of the Roar air intake system is mostly comprised of carbon fiber due to its low relative heat absorbence.

Review: After installing the Roar “Ram-Air” Intake System to the DINAN equipped 1997 1.9 we put it up against a 1998 1.9 which only consisted of an exhaust upgrade (Supersprint). Both Z3s being tested are manual and had no passengers in the vehicle. The test consisted of both 1.9s cruising head-to-head at 50mph in 5th gear. Once each front nose were equal we then cued each other to accelerate without downshifting. Both of the 1.9s remained head-to-head up until we hit 60 mph (3600 rpm) and the 1997 DINAN equipped with Roar system pulled out ahead of the 1998 Supersprint exhaust 1.9 by almost half a car length. This concluded that the ROAR system with the DINAN upgrade improves performance at higher RPM.

Other test(s) included 0-60mph runs recorded before and after the installation of the ROAR system. With a passenger operating the stopwatch, four runs were record before the installation and four runs after the installation. The results showed that after installing the ROAR system with the DINAN upgrade, the 0-60mph timing was reduced almost 3/8 of a second.

Note: testing in this manner resulted in extra weight due to the timekeeper sitting in the passenger seat. It should also be noted that potential human error is possible, due to the time it takes a human hand to start and stop the stopwatch.

Stock 1.9Roar Intake Installed

6 month update

With the Roar Ram Air System installed and after few thousand miles later, I have concluded that I am quite happy with my investment. The performance gain is a plus as well as the sound. The sound will be noticed when the engine is at load as opposed to a constant, maybe annoying, low resonance sound.

The journey of the Roar installation

After leaving several messages with Scott at Roar and no return calls, I received the package on the very day that was discussed during the sales transaction. With the help of Carter Lee (CTG) and Fred Byrom (Teachum) we immediately looked at the contents within the package and read the instructions. Let me first tell you that the instructions were vague and offered no pictures of installation. This is not a plug-n-play upgrade for those who are not ‘handy’.

Fortunately, with the help of Carter and Fred, the three of us made the installation procedures a lot easier. The first step is to remove the stock air box: unlatch four(4) clips which removes the cover and after doing so the box itself is only held down by two(2) 10mm bolts. For more detailed instructions on the removal of the stock BMW airbox, please see this article on MZ3.Net.

Tools Needed:

* 10mm socket and wrench

* 10mm bolt

* 2.5 in drill bit and drill

After complete removal of the stock air box:

* The next step is to mount the mounting bracket (a) to one of the existing posts where that previously held the stock air box. You can use either the same bolt that held the stock airbox in place or use another one.

* Take one of the filter(s) provided and spray oil on the outer shell. The oil is located in the white aero-spray can that is provided. Do not spray the inside of the filter. After spraying the filter, place it within the funnel system and tuck the filter underneath the carbon fiber nose to hold it in place.

* Get ready to drill a 2.5in. hole into the air-intake system (b) for the temperature sensor location. There should be a rubber boot for allowing the temp sensor to be inserted. The boot acts as a tunnel/bridge connection from the air-intake system to the temperature sensor.

* After mounting part (a) you then will need to install two (2) rubber washers (provided) to size match the filter system (b) prior to installing it. After this, you can insert the filter system onto the the Z3’s hose intake located where (b) is on the picture. Once installed (remember it is going to be a tight fit so you can use water to moisten the rubber washer for easier slip) you want the mounting bracket (a) to have its clamp to hold the very end (located where the Roar filter system and the Z3 intake meets) of the filter system.

* Once the clamp is successfully holding the system (do not tighten at this time) take (c) vacuum/valve cover and insert it to the air pressure vacuum hose located where (c) is on the picture. Position the vacuum/valve cover opening tilted opposite from engine (there will be a filter opening and you want it position towards the driver’s side opposite from engine). After the above steps are installed, tighten the clamps just enough so its stays in place (do not overtighten).

* Next step is to locate the temp sensor. After completing the drill, making sure it will be snug, plug the temp sensor into the rubber boot on the air-intake system that was placed.

Taking out the stock box Stock box removed Roar Bracket

Discuss this article and other Performance upgrades in the

///MZ3.Net discussion forum.

1.9 “Fogged” Airbox Modification

Pros: Increased Performance, Proven Results, Retains Stock Airfilter
Cons: The stock airbox is expensive to replace, so don’t mess up
Cost: Roughly $20, and 3 to 4 hours of your time

In the year and a half since I first posted the DIY instructions to modify the M44 Z3s airbox I’ve found that I get the same sorts of questions. I figured a document that tied all the info together would help me and those also interested in the modification. This primarily deals with the Fogged Airbox mod for the M44 but also talks about how the fuel injection system on the Z3s works as well as alternate intake products that are available and my thoughts on them. The instructions are slightly updated from my original plans to make assembly easier and to add an optional safety step.

Engine and Fuel Injection:

The fuel injection in the Z3s is a mass air fuel metering system. What this means is your car directly measures the weight of the air being draw into your engine and injects an appropriate weight of fuel (in the ratio of 14.7 parts air to each part of fuel) which it then ignites through your ignition system. Under cruising conditions and light acceleration your cars computer (DME) uses feedback from the oxygen (O2) sensors to fine tune the mixture.

The DME measures the weight of the air using a sensor called the Hot Film Meter. (HFM) The HFM is basically a film through which a current is passed to heat it. If you were to look at the inside of your HFM you will see that the film is very small and it actually only samples a small fraction of the air that passes through the meter. By measuring the temperature change of the film (and knowing the intake air temperature) the DME is able to calculate the mass (weight) of air that is flowing over the film. It can then calculate the total mass of air flowing through the HFM. This works if the airflow through the meter is smooth and evenly distributed, in other words laminar flow. The DME then uses this to determine how much fuel needs to be injected to keep the AFR at 14.7/1, also called Lambda=1. An AFR of 14.7/1 results in the most complete combustion of your fuel which gives you the least emissions. If an engine is running rich OR lean (more or less fuel to air) the engines emissions will increase. At full throttle the DME runs the engine richer for more power.

Now a key point… if you increase the airflow into your engine, the DME will measure it using the HFM (assuming smooth airflow) and will increase the fuel injected to compensate. The DME must do this or your engine would run leaner which would increase emissions. If you increase the amount of air, to keep the ratio between air and fuel at 14.7/1, the DME must add more fuel. If you increase airflow and burn more fuel you have increased your power output.

Problem:

As delivered from BMW the M44 engine in the Z3s really is not as rev happy as say the engine in a Miata. Above 5000 rpm the power feels like it has reached a plateau and there isn’t much more to be gained by revving the engine higher. The reason for this is because up high your engine’s ability to breathe is being restricted. I wanted to see if I could correct this and verify an improvement.

After looking into the intake systems that were on the market or known to be ‘in the works,’ I determined that there was nothing out there that I would put on my car. The following are a few of the setups I found and some of my reasons for rejecting them:

Drop in K&N filter ($40): in my opinion, K&N filters do not filter as well as your stock paper filter. I will not put one on my car. Your filter is the first and only line of defense against letting dirt into your engine. The K&N is made from an oiled cotton gauze, if the oil dries out the ‘filter’ basically stops all filtering. I have heard it said that when a K&N filter gets wet the water can ‘wash’ the previously filtered dirt right through it and into your engine. The person who told me this raced motorcycles and said that when he switched from K&Ns back to paper filters his engines lasted much longer between rebuilds. Lastly, Greg Hudson had performed dyno tests comparing a new stock paper filter against a new drop in K&N filter… the result was a LOSS of power with the K&N. That demonstrates that the paper filter isn’t what is limiting airflow as the paper filter has a huge amount of surface area for the size of our engine. Swapping filters does nothing to address the real source of restriction in your intake.

K&N Filtercharger cone filter ($149): Has a lot of problems. It has the same filtering concerns as the drop in filter and the rest of the setup adds a few more problems. The cone filter can suck in hot radiator air which will hurt performance. This is because cooler air is denser air (heavier), the more air weight you can get into your engine the more fuel will be injected and the more power you will get out of your engine. The circular shield that some sell might help a little but it will also increase restriction as it blocks the filter somewhat. It still doesn’t get all that great of a source of cold air either. As with most other cone setups the tube that connects the filter to the HFM changes diameter at the cone filter and at the HFM. Those ‘adapters’ are not a good idea. When they increase or decrease in size it will cause turbulence and restrictions in the airflow. For the HFM to meter the air weight properly it needs a smooth flow of air through it. The connecting tube changes size right at the start of the HFM, this could cause turbulence which would result in improper metering by the HFM. If the HFM isn’t able to properly measure the airflow into the engine the DME is going to be injecting the wrong amount of fuel. This will keep the engine from running optimally and won’t be making the power it should. Additionally, the filter is right in front of the HFM and the airflow doesn’t have much space to ‘settle down’ so it will still be turbulent from passing through the filter itself when it hits the HFM. There will be more on this later.

Art of ROAR cone filter (~$200): Mostly the same problems as the K&N setup above.

ECIS (~$200, when available): Uses a K&N cone filter so it has all the same filtering concerns and most of the other problems except it has a shield behind/besides the filter to block off the filter from the rest of the engine compartment to help with the heat problems.

Dinan Cold air intake ($299): uses a K&N cone filter so it has all the same filtering concerns. It positions the filter behind your foglight to avoid the hot engine air problem but exposes it to more water. Has the same type of ‘adapters’ and the problems they can cause that all the above cone filter setups share.

What I was looking for was a setup that kept the paper filter (they filter well.. even when wet) that had a smooth airflow to the HFM for proper metering, and had a good source of cold air but that allowed the engine to breathe better.

Factory airbox setup:

On the stock M44 airbox the air intake is in a snorkel between the passenger side headlight and the edge of the radiator. The snorkel has a fairly narrow opening which may limit airflow somewhat plus it isn’t in a direct path of air, the hood support blocks it somewhat. From the snorkel the air flows through a 2 5/8″s insulated hose over the top of the radiator then down the other side where it connects to a plastic funnel on the airbox itself. Each turn causes restrictions.That funnel has a 1 3/4″ opening into the airbox itself and is ,IMO, the biggest source of restriction in the intake.

After the air is inside the airbox it has a good amount of area to expand to evenly pass through the filter then changes over to the HFM as BMW designed for proper air metering.

The solution… aka the ‘Fogged Airbox’:

It increases the air intake hose into the airbox to a 4″ diameter hose. That is about a 700% increase in surface area for air to flow through easier. The setup grabs its air from behind the foglight for a good source of cold air. It keeps the paper filter for maximum engine safety and the flow to the HFM is exactly as BMW designed it. In my opinion, it addresses the real problems with the factory airbox and doesn’t create any additional problems like the other setups do. It costs around $20 and takes about 3-4 hours or so to build and install.

Testing, Does it work?:

Instead of using formulas and/or a flow bench I tested the best way possible, the actual DME measured airflow into my engine. This is the ideal way to test because if your intake/engine has a bigger restriction elsewhere the formula/flow bench methods will give you misleading numbers that won’t be realized in the real world.

As was mentioned above the DME in the Z3s has a hot film sensor to calculate the actual mass (weight) of the air flowing across it based on the temperature of the film. The cooler the film is the more air mass that has passed over it. If the airflow is smooth through the HFM it will be metered properly. From this and a few other sensors the DME can calculate the mass of the air being taken into the engine. In other words, your DME knows exactly what the airflow is… all I need to do is have the DME tell me that information on before/after runs and compare the two.

Getting that data is actually very easy, provided you have the proper tools. OBDTOOL plugs into the OBDII port on your car and can grab data directly from the DME. For this test I need to grab airflow (expressed as pounds per minute) and engine RPM and log that, in real time, to a file.

Grabbing the data is easy. You set OBDTOOL to log the data to a file, drive at about 1000rpm in second or third, then just floor it till redline. When you are logging two data points (airflow + RPM) OBDTOOL is able to receive 2-3 updates per second. To get more data points (for more accurate airflow curves) I made multiple runs and merged the data points together. The higher the gear you are in the more data points you receive as well.

For the first set of data I made 3 runs with my car in its normal modified state. That includes the Fogged airbox , a +3mm big bore throttle body and a Remus exhaust. My car is a ’96 without traction control so it doesn’t have the secondary throttle body in the air stream.

Since I’m interested in just the effect of the airbox mod that is all I changed for the second set of runs.

There is one slight problem though… I can’t get my airbox back to exactly stock as I modified my personal airbox. The factory stock setup has that 1 3/4″ diameter inlet into the airbox which is the largest source of the restriction in the intake system. So I made a 4″ diameter plate (size of the Fogged’ airbox inlet) that has a 1 3/4″ hole in the center to simulate having the stock inlet in the airbox. This plate fits right in front of the rodent screen on my inlet and is held in place by it with tape around the outside edges to seal better. Because the airflow on the incoming side of the restrictor plate is still less restrictive (because it is still attached to the 4″ hose of my setup vs. a 2 5/8″ hose and the stock snorkel ) the airflow numbers recorded are probably higher then if the airbox was fully a stock setup. Still, the test will give a fairly accurate result of the real world results of opening up that stock 1 3/4″ inlet to 4″s.

Looking at the graph (click on the picture to the right for a larger view), at low RPMs the Fogged’ box seams to flow a bit better than stock. In the midrange the flow is basically stock, then at 4000 rpm or so the difference begins to grow and above 4800 it grows very quickly. The difference is about an 8.5% increase of air flow at 6400 RPM. That means your engine is burning about 8.5% more fuel there too… which also means you are producing about 8.5% more power! In fact because you are getting more air in the cylinders at higher RPM (increased volumetric efficiency) you will have a higher effective compression ratio and you will extract slightly more power from the air and fuel you were already burning before the mod in addition to the extra power for the extra air and fuel.

Now my thoughts as to why the ‘Fogged’ midrange flow is nearly stock. Simply because in that range the stock airbox is not the limiting factor. I assume if there is a problem (the cylinders could be filling to capacity) that it is the intake manifold in that range. Above 4800 rpm the DISA setup has changed over the butterfly in the manifold and the stock airbox was limiting flow again.

As an aside I also tested the intake air temperature. According to my center console computer it was 70 degrees during the test. The intake air temp. (as read from the DME using OBDTOOL) was 75 degrees while just cruising around and when I floored it for a few seconds it dropped to 73 degrees and stayed there.

I’ve tested a similar mod on a 318ti and recorded about a 5% airflow increase. That car was a ’97 with the additional throttle body in the airflow (read extra restriction) and it the rest of the engine was totally stock.

I’ve also done before/after 0-60mph runs using a G-Tech Pro. With just the Remus exhaust I was able to get a best time of 8.1 seconds. After the airbox, throttle body and Garrett Lim’s software (with stock 6500 rpm rev-limiter) my best times dropped to 7.45 seconds. My software was overwritten last December, by the way. Since then I have run stock software with the box.

Tools you need to build it:

Something to cut a hole in the plastic airbox. You could use a 4 1/8″ hole saw, reciprocating saw, Dremel or whatever else you feel comfortable with.

A Dremel with a heavy duty cutting wheel, a grinding stone and if you are using it to make the main hole the dime sized metal bladed circular saw and one of the grinding stones.

Eye protection (you are going to need it!)

10 mm socket and socket wrench

Hot glue gun with extra strength glue

Regular screwdriver

Permanent marker

Scissors and Wire cutters

Optional but recommended: Propane torch and plumbing solder, only needed if you are going to install the rodent screen in the inlet

Stuff to buy:

Go to the nearest Home Depot or the like and in the ventilation section get an aluminum 5″ to 4″ duct adapter. This is a tubular piece to allow a 5″ hose to plug into a 4″ hose and should cost about $3.

Optional but recommended: While at Home Depot in the ventilation department you need a ‘Rodent Blocker’ which is just a square piece of heavy mesh which is meant to go on your clothes dryers exhaust to keep mice from getting into you house. Figure a buck or two for this.

Go to a Pep Boys or whatever and in their ventilation section they should have a 4″x72″ air intake type of plastic hose for under $15. Anything similar should work OK but make sure it’s flexible. The stuff at Pep Boys worked really well and is very smooth on the inside for better air flow. Also get a 4.25″ hose clamp for a buck.

Very optional: can of flat black spray paint… high temperature outdoor gas grille paint works OK

Making the inlet:

First thing you need to do is to make the 4″ inlet out of the adapter you bought at Home Depot. To do this on the expansion funnel (between the 4″ and 5″ tubes) you need to cut/drill the two rivets. This lets you separate the adapter into 3 pieces, the 4″ tube, the expansion funnel and the 5″ tube. We only need the 4″ tube with the ‘rib’ on the side that was connected to the expansion funnel which opened up to the 5″ piece. The 4″ diameter tube will become your inlet into the airbox.

Optional but recommended: Cut down the ‘Rodent Blocker’ to a circle that will just barely fit inside the ‘rib’ on the inlet and solder it in place. This is a safety step to be sure a rodent doesn’t climb up your airhose and decide to make a nest in your airbox.

Very optional: spray paint the intlet. Paint doesn’t stick very well so it will take multiple coats. I’ve found that it helps if after each coat of paint you ‘bake’ it on with a hot air gun but even then it can come off fairly easily.

Completed inlet along with the airhose and hose clamp. This is all the parts required for the Fogged airbox.

Adapting the airbox:

It would be helpful if you have the car up on ramps or jack stands but it isn’t required. You need to get the bottom half of the airbox out of the car. To do that release the four clips holding the top of the airbox on and move the top aside. Take out the air filter and put it somewhere clean till you are done. On the fender side of the airbox there are two 10 mm nuts holding the air box in place. Remove them.

Above the radiator is the big black plastic box which holds the stock intake hose. Take the cover off of this by removing the (4) 10 mm bolts. Two are right in front of the plastic box in plain sight, the other two are right behind the plastic box. Lift the cover of that off and put it out of the way. You will now see the stock hose and where it connects to the snorkel on the airbox. Just pull that hose off and the bottom of the airbox can be removed from the car. While you are at it disconnect the other end of the stock hose and remove it from the car as it’s not needed.

Now with the bottom half of the airbox out of the car remove the external snorkel from the box. There is a clip on it that will let the snorkel slide off the box. Notice how tiny the hose is at the end of the snorkel! Next the internal funnel needs to be removed. There is a clip on the top of that and another clip on the opposite side of the box that lets you take the plastic frame out along with the sound deadening material. Don’t worry if you break some of the plastic frame pulling it out… I left mine out and it’s not a problem.

Now comes the fun part, you need to cut a 4″ hole where the stock hole is. Put the 4″ side of the inlet over the hole, on the outside of the airbox, and draw a new circle on it with the marker. Don’t center the new hole over the old one. You basically want the new hole to be as far forward on the airbox as you can make it. You need the inlet to be forward so it can clear your steering reservoir when you reinstall the box.

Now PUT ON YOUR EYE PROTECTION!!!!! – Using whatever method you decided on, cut out that 4″ circle. This is the most time consuming part of the project as hot, nearly liquid plastic is going to be flying around so be careful! Be sure to also look inside the airbox as in a couple of places there are plastic ribs and such that you need to cut from the inside for the hole to come out. After you get the hole cut out test fit the inlet into it. The inlet should fit through the hole but stop at the ‘rib’ on the inlet. For the test it is easier if you just put the 4″ side through the air box from the outside but this isn’t how it will be when you are done. If you can’t get it to fit use the grinding wheel to smooth and enlarge the hole. It should be as tight a fit as you can make it without distorting the inlet. After you have the inlet fitting in the hole remove the inlet from the airbox. Scrub out the inside of the air box with a brillo pad or something similar to remove all the plastic bits that got thrown around when you cut the hole. After you get it all cleaned out dry it.

Now put the inlet into the airbox for real. The side with the rib goes inside of the box with the 4″ tube pointing out the hole. Only have the tube protrude from the box up to the rib on the tube hitting the inside of the airbox. The rib will keep the inlet from pulling through the box if you cut the hole properly. Now from the outside of the box seal the inlet to the box with the hot glue.

A slight air leak here isn’t critical, as it’s still before the air filter, but do the best you can. Do NOT use a silicone glue as it could cause problems with your O2 sensors.

After the glue has set, slide the 4″ air intake hose over the inlet protruding from the airbox. It is a very tight fit but if you take your time and work it around the inlet you will get it on. Secure it in place with the hose clamp. Do not overtighten the hose clamp as you could deform the inlet. You could cut the length down to about 3-4 feet now or you can wait till it’s installed then cut it.

Now reinstall the airbox into the car. The tube and hose should just fit into the car but it will fit if you cut the hole in the proper position. You can either put the old air intake cover back over top of the radiator and put back in the (4) 10 mm bolts or pull the bottom half of the plastic assembly off of the fan shroud and out of the car. I took it out of my car but if you want your intake to look stock leave it all in place.

Reattach the (2) 10 mm nuts holding the airbox in place. Put the air filter back into the airbox and secure the cover with the 4 clamps. Be sure you get a good seal. Now would be a good time to replace your air filter if you haven’t in 10k miles or so.

Route the hose pretty much straight down along the side of the radiator. This is easier to do from under the car but is manageable from above. Run the hose into the opening that leads into the front bumper, right in front of the wheel and place the hose opening behind the foglight. Trim the hose as needed to do this. You may want to disconnect your battery for a few minutes to reset the long term fuel trim (adaptation) that occurs in your DME but it isn’t really needed.

At this point you are done. You too now have a Fogged Airbox. Go take your car for a spin and run it up to redline a few times! You are going to love it!

Fogged Airbox FAQ:

(Q) Why not put the hose in front of the radiator or below the car or add a scoop or where ever?

(A) I’ve tried a scoop and it resulted in no measured airflow increase. It also greatly increases your chances of hydro-lock. Putting the hose behind the fog light gives good airflow and you would need to drive through a VERY deep puddle (several feet) before you would have a problem. Hydro-lock occurs when you fill your combustion chamber with enough water to stop the piston on its compression stroke. When this occurs you cause major damage to your engine. Even if you submerged your hose in water I don’t think the M44 creates enough vacuum to suck water up the 4″ diameter hose, then fill the airbox and finally draw it into the combustion chamber. If it was 1″ diameter hose, yes but not the 4″ hose. Your airbox has a drainage hole in it that would act as a vacuum relief if the main hose was submerged. Having said that it doesn’t mean I recommend that you drive through very deep puddles. You are not a U-Boat captain after all. You also want to limit the number of bends the hose needs to make as each bend will cause some restriction. Keep it simple and put the hose behind the foglight, it works.

(Q) Won’t rain get behind the fog light and get into the intake?

(A) Yes, but small amounts of water isn’t a problem. This can happen on the stock setup during driving in the rain or on very foggy nights. It basically wets your filter and since it is still a paper filter there is no problem.

(Q) Won’t I get check engine lights? IE… Dinan says that if the mod worked it would cause Check Engine lights as the DME won’t know how to deal with the airflow. They also claim the engine will run lean with any air intake on it and no ‘Stage II’ software in the car.

(A) Simple answer: No

Much longer answer: I’ve put around 15k miles on my car and never had a Check Engine light. No other Z3 owner that has done the mod has had lights that were caused by the Fogged airbox either. Remember how your fuel injection works, the HFM directly measures the airflow into your engine and injects the appropriate amount of fuel. It ‘knows’ how to deal with the increased airflow. This is assuming proper air mass metering by the HFM. I have done wide open throttle (WOT) runs recording my O2 sensor data vs. RPM to see what mixture I’m running at. At WOT my engines goes rich (O2 data at 0.8v) from right off idle and stays very consistent (+/- 0.05v) all the way to the rev-limiter. IOW, with the Fogged airbox the HFM is properly metering the airflow increase and the DME is adding fuel as needed throughout the rev range. This is with stock BMW software in my DME. If this was not the case the O2 voltage would drop off (go leaner) as I got above 4k RPM where the airflow increase occurs. On other types of fuel injection: air-flow metering or speed/density the DME would NOT be able to measure the additional air and they would need a ‘chip’ or ‘software’ to properly deal with the increase flow. On our cars this is NOT the case.

Even IF what Dinan claims was true (in that it applies to ALL intakes, it is not true) why wouldn’t the ‘Stage I’ software (which makes your engine run slightly richer at WOT and slight advances your timing) be enough? A theory on that: Assume for a second you have two intakes.. their actual airflow into the engine is the same. But one intake has smooth laminar flow at the HFM and the other intake has turbulence at the HFM. What would happen when you put them on your engine? Again, if you look at the inside of your HFM you will see that it actually only samples a small fraction of the air that passes through it. Based on that small sample it calculates the total air mass. This works fine if the airflow through the HFM is nice and smooth. In the case of the intake with smooth airflow through the HFM if you increase the airflow through the HFM your DME will properly measure the airflow increase and add fuel as required. In it’s maps it says for ‘A’ amount of air inject ‘X’ amount of fuel. Because the metering is accurate you are running at the proper air to fuel ratio.

Now what happens if you put on the intake that flows the same amount of air but causes turbulence at the HFM? Because the HFM only samples a small part of the airflow if the airflow through the HFM is turbulent the HFM will NOT properly meter the mass of air flowing through it and the DME will inject fuel based on the INCORRECT metering. You could end up running richer or leaner depending upon which direction the metering was off. The DME reads that you are taking in ‘B’ amount of air so it injects ‘Y’ amount of fuel. Since you are actually injesting ‘A’ amount of air (it was just mis-metered by your HFM because of turbulence) you should be injecting ‘X’ amount of fuel. But because it is in fact injecting ‘Y’ amount of fuel you are NOT running at the proper air to fuel ratio.

So, what can you do about this? Either smooth out your airflow for proper metering OR add a ‘correction’ (re-calibration) into the DMEs maps so that when it meters ‘B’ amount of air (still actually flowing ‘A’ amount) it in fact injects ‘X’ amount of fuel. This would result in you running at the proper air to fuel ratio.

If you ran that ‘correction’ on a car that meters its air properly (say a stock airbox, or an intake with smooth airflow that metered properly) you would end up running at the wrong air to fuel ratio. Hence, ‘Stage I’ and ‘Stage II’

(Q) What is laminar airflow and why is that important to your HFM?

(A) This is an attempt to explain it, not the best example but it was all I could think of. Picture six lines of people all running parallel to each other waiting to get on a subway.

Subway

A B C D E F

A B C D E F

A B C D E F

A B C D E F

A B C D E F

A B C D E F

A B C D E F

A B C D E F

RULE: When lines C and D move forward 1 person lines B and E move forward 1/2 a person and lines A and F move forward 1/4 of a person. Knowing this and starting at the front of the lines by watching the people in any single row (A,B,C,D,E or F) you can determine how many people total have gotten on the subway. For example if the first person from row A just got on the subway you can calculate that a total of 14 people have boarded the train. You use a small sample to determine the total knowing the ‘flow’ characteristics. This is what your HFM does but for air mass flowing into your engine.

(Q) Will I really feel the difference? Can it really work that well for so little money?

(A) Yes!!!

I have a very hard time convincing people that this works as well as it does. I’ve never heard from a person that has done it and not been thrilled at the difference. Above 5000 rpm it feels like a totally different engine. Now your engine pulls HARD all the way to redline. You might even hit the rev limiter a few times while you get accustomed to the difference.

(Q) Do you really think BMW screwed up on the airbox design that much?

(A) I think they met their design goal, so in that sense they didn’t screw up at all. Their engineers had to make a compromise between noise and airflow. The stock airbox acts like a ‘muffler’ for intake noise. Just like any other muffler this limits airflow somewhat in the pursuit of reduced noise. The Fogged mod is sort of like putting on a straight pipe for your intake. It lets air in easier but it also lets intake noise out easier. Under acceleration you will get a little bit of an intake roar but it sounds great and is perfectly appropriate in a sports car.

(Q) What do you get out of all of this?

(A) Besides the satisfaction of helping out other M44 Z3ers, nothing. 😉 To that end if you do Fogg your airbox please e-mail me or preferably post a message on the Z3 message board with your opinions on it.

(Q) But xxxx tried a K&N and noticed a huge difference in performance, why?

(A) Most of the people I’ve talked to that tried a K&N decided to give it a try when it was time to replace their paper filter. The reason they felt the increase in performance wasn’t from the K&N itself but because their paper filter was clogged and needed to be replaced. If they had just put in a new paper filter they would have felt the same thing. I replace my filters every 8-10k miles, I can tell when they need to be replaced as my gas mileage starts to drop.

Photographs courtesy of Rich Carlson, Robert Leidy and Tom Mosteller, thanks guys!

The Fogged airbox is copywritted by Shawn Fogg and is for individual use only.

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