Performance Exhausts for the BMW Z3

Exhaust Articles

  • 1.9 Remus
  • 1.9 Borla
  • 1.9 Supersprint
  • 2.8 Supersprint
  • 3.2 Tri-Flo
  • 3.2 Supersprint
  • 3.2 Remus
  • Exhaust Articles

    1.9 Remus

    1.9 Borla

    1.9 Supersprint

    2.8 Supersprint

    3.2 Tri-Flo

    3.2 Supersprint

    3.2 Remus

    Performance Exhausts for the BMW Z3

    May 31, 1999

    By: Robert Leidy

    Inside each cylinder, the BMW Z3’s electronic control module injects a calculated mixture of air and fuel. This mixture is then ignited which produces power. However a by-product is also produced from this process which is commonly referred to as exhaust. The burnt gas fumes (exhaust) exit the cylinder and travel through a pipe commonly referred to as a header. The header pipes from each cylinder are then combined and channel the exhaust fumes from the engine into a catalytic converter. The catalytic converter is a device filled with a metallic-mesh-like filter that removes some of the pollution from the exhaust fumes. Once the exhaust has passed through the catalytic converter, it is channeled through a single pipe to an exhaust resonator, which reduces some of the sound produced by the engine. Once the exhaust has passed through the resonator it is channeled to a muffler to “muffle” additional sound from the exhaust. Once the exhaust travels through the muffler it exists the Z3 via tail pipe(s) under the rear bumper.

    The theory behind performance exhausts is that each device that the exhaust fumes pass through cause resistance, which in turn increases the amount of air pressure inside the exhaust. The pressure built up also effects the cylinder because “back pressure” from the exhaust is putting additional effort on the cylinder as it is handling the next mixture of air and fuel. A performance exhaust is designed to reduce the amount of resistance in the exhaust making the exhaust flow more freely and reduce and amount of “back pressure”. In order to accomplish this, those devices within the stock exhaust that cause resistance can either be removed or redesigned to be less restrictive. However each component of the stock exhaust is there for a reason. The muffler is designed to remove sound at the cost of exhaust resistance. You can redesign a muffler to have less resistance but in general you will also be decreasing the mufflers ability to “muffle” sound. As with most things in life it is a give and take relationship. Finding the correct balance of give and take is a judgment call, so it can be different for different personal tastes.

    There are varying degrees an owner can take to reduce the pressure in the exhaust and increase performance of the engine. Perhaps the easiest way is to just replace the muffler. Or for a little more performance, replace the muffler and resonator. Professional racers like Mark Hughes remove all of these resistance-causing devices. However removing the catalytic converter would keep a Z3 from being street legal (which is not a problem for the Z3 Race Team). The most common after-market exhaust systems are called “cat-back exhausts”. With the design of the Z3 these “cat-back” systems bolt right onto the stock catalytic converter and replace everything “back” from there (keeping the Z3 street legal). The new pipes are larger, the resonator is removed and the muffler is less restrictive, so exhaust can exit the engine/exhaust with less resistance. This has two effects on the Z3, it increases the performance and it makes the Z3 louder (more sound from the exhaust).

    So now that we’ve covered the theory behind performance exhausts lets look at the type of decisions an owner would need to make in evaluating after-market performance exhaust systems:

    Stock Engine/Exhaust Design:

    The theory behind performance exhausts is that reducing the amount of pressure increases performance. So it only makes since that the amount of potential performance gain is directly related to the amount of resistance/air-pressure-buildup in the stock exhaust. In other words if the stock exhaust is very restrictive then there is a lot of potential performance gain.

    Assuming that between the different Z3 engine configurations the restrictiveness of the various BMW stock exhausts components is roughly the same, we can make some general observations looking at the different designs. The 1.9 Z3 is a 4-cylinder engine, the exhaust output from all four cylinders is combined before entering the single catalytic converter. So roughly 1.9 liters of exhaust output is sent through the stock exhaust each time the gas inside the cylinders is ignited.

    Compare that to the 6-cylinder 2.8 Z3, which has the exhaust output from all six cylinders combined before entering the single catalytic converter. So roughly 2.8 liters of exhaust output is sent through the same pipe. Comparing these two it would appear that the 2.8 would benefit more from a performance exhaust than the 1.9 would since 47% more exhaust is traveling through the exhaust.

    To continue the comparison, the 3.2 Z3 is also a 6-cylinder engine. However the exhaust output is split in half, the output from three cylinders is sent to the first catalytic converter, with the exhaust output from the other three cylinders is sent to a second catalytic converter. The exhaust output from each half is never mixed so in reality the each exhaust is only handling 1.6 liters of exhaust output. Comparing this output it would appear the 3.2 engine would benefit the least from an after-market exhaust.

    Metal Used:

    There are also differences in the type of metal used in exhaust systems, the big differentiation is it, or is it not stainless steel. The big advantage to stainless steel is its durability. If you live in an area where salt is used on roads then you know that rust can eat up car parts. For these areas stainless steel will last a lot longer so the increased price is easily justified. The other advantage to stainless steel is that it conducts 2/3 less heat than mild steel, which helps to keep temperatures in the exhaust to a minimum. However stainless steel also expands 40-45% more than mild steel when heated so fitting a stainless steel exhaust is slightly more difficult. (The stock exhaust system is not stainless steel).

    Exhaust Tips:

    Choosing exhaust tip style is usually a 90% cosmetic decision. However the type of exhaust tips also effect how the exhaust will sound. If the exhaust tip is angled up the sound will generally be louder, if the exhaust tip is angled down the sound will generally be quieter. Most exhaust tips point straight back just like the stock exhaust does.

    In the United States, five different engine configurations have been built in the Z3:

    M44: model year 1996-1998

    The M44 1.9 liter engine was the first Z3 sold in the United States. Several companies make performance exhausts for this Z3. However this engine configuration is no longer being made for the US market so it is doubtful that any additional aftermarket performance exhausts will be added to the list.

    Borla

    Remus

    Supersprint

    M52: model year 1997-1999

    The M52 2.8 liter engine was the second Z3 engine configuration to be sold in the United States. Several companies make performance exhausts for this Z3. However this engine configuration is no longer being made. BMW now has a new M52TU 2.8 liter engine that is different in design, so exhausts for the M52 Z3 will not work on the M52TU Z3 and via-versa.

    Borla

    Remus

    Supersprint

    S52: model year 1998-2000

    The S52 3.2 liter engine was the third Z3 engine configuration to be sold in the United States. Several companies make performance exhausts for this Z3 (officially called the M roadster and M coupe).

    Remus

    Supersprint

    Tri-Flo

    MXXTU: model year 1999-2000

    The MXXTU 2.3 liter engine is the forth engine configuration to be sold in the United States. MZ3.Net does not know of any M52TU Z3 “cat-back” performance exhaust systems at this time.

    M52TU: model year 1999-2000

    The M52TU 2.8 liter engine is the most recent engine configuration to be sold in the United States. Supersprint is the only company that MZ3.Net has heard that currently has a cat-back exhaust ready for the new 2.8 liter engine. Supersprint’s part numbers for the new exhausts are 78.67.06 or 78.67.66. I assume the two different numbers are for different exhaust tip options.

    Discuss this article and other Performance upgrades in the

    ///MZ3.Net discussion forum.

    Clear Windscreen

    Pros: Better visibility, Good at blocking wind, Cost, Blocks/reflects sound, Makes installing the boot cover easier
    Cons: Blocks access to rear storage area (for those without the subwoofer), Blocks access to the area behind the rear console when the top is up.
    Cost: $85 includes shipping (fromwww.roadster.8m.com)

    My first Z3 was a 1997 1.9, and one of the first “accessories” I wanted was a windscreen to cut down on the amount of back draft that was hitting the back of my head. My desire for the windscreen was greater than my patients when I learned that BMW’s windscreen was available in Germany but not in the US. Even the Atlantic ocean could not keep me away from that windscreen, I had a Z3 owner in Germany purchase the windscreen from his BMW dealership and mail it to me.

    Once that 1st windscreen was installed I was forever a windscreen fan. However when I traded in that 1997 1.9 for a 1998 3.2 the old windscreen wouldn’t work with the new Z3 because of the roll-hoop rollbars. BMW had a new windscreen for the roll-hoops, so without hesitation I purchased the new BMW windscreen when I ordered the car. The new design didn’t stop wind as well as the original design but it was good enough and since the only other alternative was no windscreen at all it was a easy purchase decision.

    I’ve spent over a year with the BMW roll-hoop windscreen, and I have to admit that a year later I’m concerned about the amount of wear the BMW windscreen is showing. In some places the black material has faded to a yellowish brown, it appears to be sagging in the middle and the single support rod that runs inside the top of the windscreen has torn the material in a couple places. It still functions as well as it did when it was brand new but it is starting to look worn and ugly (at least to this owner).

    As luck would have it another windscreen option opened up for me. A Z3 owner named JD was contemplating purchasing the BMW windscreen, but there were some aspects of the BMW windscreen that he didn’t care for. After a discussion on the Z3 message board JD set out to make a clear Plexiglas windscreen on his own. When word spread of his clear windscreen plans several other Z3 owners expressed an interest in his efforts. One thing led to another and now JD is in the windscreen business. After watching the $100~$150 BMW windscreen wear over the first year I decided to try JD’s clear windscreen.

    Installation

    Before long a long slender box was waiting for me on my doorstep. JD shipped the box well labeled as fragile to ensure the safety of the contents inside.

    When I opened the box I found instructions, six Velcro straps, some foam padding and a Plexiglas windscreen with protective tape around it. The instructions informed me that this was version 5, an improvement over the previous version in which some modification were made to the shape to improve its abilities as a windscreen. The instructions also walked me through the brief assembly and installation.

    Note: With the instructions below, the text in red is from the original instructions that came with the windscreen. The additional black text are my own comments in relation to that step.

    Remove protective paper by carefully peeling it off.

    This takes a little longer than you would think it would. The protective backing is stuck onto the glass but peels off cleanly. Be careful around the edges of the Plexiglas because it can be sharp.

    Take one of the short pieces of the protective rubber tape and place it 1/8 inch away from the edge of the windscreen. Start from the outside edge and work it around the curve. Finish it off in the center

    Included in the instructions is a template, you can lay the clear windscreen over the paper template and it will show you were to install the rubber padding.

    Now do the same on the other side.

    Make sure the curve of the tape is even and smooth. This tape serves as a cushion between the windscreen and the roll-hoops.

    Insert the straps with the soft fuzz on the inside so that it will face the roll hoop.

    There is no more soft fuzzy side. JD improved the strap design, the new design is stronger and easier to work with.

    Do the same for all the strap locations. Straps need only to overlap about 3/4″ to be secure. They may seem a bit tight at the bottom location.

    The windscreen is held in place with three straps per side, one of the straps is longer than the other two and the longer strap is for the lower part of the inner support.

    Position the windscreen in front of the roll hoops and behind the seats. It may help to move the seats forward for access.

    The bottom of the windscreen has a foam/rubber padding on it so you can rest the windscreen on the top of the rear storage area. However after properly installed the top edge of the windscreen should follow the curve of the roll-hoops and leave a gap at the bottom of the windscreen.

    Secure the straps around the roll hoops. Put a slight amount of tension on it, especially at the lower strap so that it bows in just a little. This will eliminate any vibration.

    You can “scoot” the straps around so that the end of the overlap edge is up in the cutout portion. That gives it a much neater appearance. To eliminate the static build up and also to clean your windscreen, periodically apply one of the many brands of plastic cleaners. Do not use any abrasive cleaners on the plastic.

    Once the windscreen was installed my initial reaction was positive, however I wanted to wait before making up my mind. I decided to give this new windscreen a couple months and then record my feelings about it rather than make any snap judgements. There were a couple upcoming Z3 events so I knew I could get other’s opinions as well.

    Long Term Update

    After the initial installation JD contacted me and said he was working on some different straps to secure the windscreen in place. The original straps I had received with the windscreen were solid Velcro with differing material on the two sides, the straps worked well for me but JD was concerned that the straps might not hold out well over time.

    JD tried a couple different straps before coming up with the ones pictured to the right. The new straps hold the windscreen firmly in place and appear to be well constructed.

    Since there are now two windscreen designs available for those Z3’s with roll-hoop rollbars, it only makes since to compare the two designs against each other. Each design has its strengths and weaknesses, the following is a discussion on each aspect of a windscreen and how the two compare against each other.

    Cost

    The BMW windscreen usually sells for around $150 from the average BMW dealership. You can mail order the BMW design for roughly $108 including shipping. JD charges $85 for his design and that price includes shipping. At least for me the BMW design started showing a lot of wear and tear after the first year. We’ll have to wait to see how the Clear Windscreen holds up but currently it appears to be doing fine.

    Ability to decrease the wind turbulence

    Comparing the two designs I can tell that there are differences. At times the BMW design seems to do better on really windy days, especially with strong side gusts. However I think on the average day the Clear windscreen might stop more wind. Its really too close to tell both do an adequate job.

    Rearward Visibility

    Personal preference is going to make this different for different individuals, but for me I prefer the increased rearward visibility that the clear windscreen offers. The BMW mesh windscreen is harder to look through which has its advantages and disadvantages.

    At night the BMW design decreases the light that comes from the headlights of cars behind you, but in general I always felt a little blind at night with the BMW windscreen. On the positive side, the BMW mesh windscreen can also function as a sun shade if you park your car facing away from the sun. In regard to rearward visibility this is where the two windscreen designs differ the most, some will prefer the increased rearward visibility with the Clear windscreen, some will prefer the privacy and decreased visibility of the BMW windscreen.

    Cabin Noise

    Although not intended in its design, the clear windscreen also seems to change some of the acoustical characteristic of the Z3 interior. The solid Plexiglas appears to function as a sound wall that blocks some of the road noise coming from the rear of the car while also reflecting some of the stereo sound back into the middle of the cockpit.

    Access to rear storage area (for those without the HK subwoofer)

    The BMW windscreen is designed to rest against the back side of the rear compartment. The advantage to this design is that those Z3 owners that don’t have the HK stereo have a storage area back here and can lift the lid while the windscreen is installed. The version 5 Clear Windscreen blocks access to this storage area since it installs over the lid. However if you have a Z3 with one of these storage areas JD makes another design (version 4) that rests on the back side of the roll-hoops allowing the storage compartment to be opened.

    Installation

    Both windscreens can be installed and uninstalled somewhat easily. The BMW design uses clips that snap the windscreen in place holding it down over the roll-hoop rollbars. The clear windscreen uses six Velcro straps to tie the windscreen to the front of the rollbars. If you use the BMW boot cover the BMW windscreen interferes with the rearward snaps making installation more difficult. The clips on the BMW windscreen can also come in contact with the clear plastic window when the convertible top is lowered/folded. Some owners have reported scratches in the clear window from the BMW windscreen clips. The clear windscreen’s installation does not come close to the lowered/folded convertible top.

    I guess the bottom line is that I like JD’s Clear windscreen design over the BMW design. For me the important facts are (a) it blocks wind just as good, (b) costs less than the BMW windscreen, (c) gives me better rearward visibility and (d) should last longer than the BMW design. I now own both windscreens and have decided to use the clear windscreen for these reasons. There might be times when I go back to the BMW design but for the majority of the time the clear windscreen is now standard equipment on my Z3.

    X-Pel’s Invisible Bra for the Z3

    Pros: Protects the fragile paint on the Z3. Hard to detect from a distance of 4 or more feet.
    Cons: Moderately hard installation
    Cost: Contact XPel at http://www.xpel.com/ or 800-447-9928
    The Days Events

  • Gathering at Rory’s
  • Fixing Paint Chips
  • X-Pel
  • Swapping Mirrors
  • Boot Cover Swap
  • Chrome Front Grill
  • The BMW Z3 is painted with EPA backed “environmentally friendly” paint. The makers claim that the new paint is less susceptible to fading and oxidation, but an apparent downside is that the new paint is much more brittle. While BMW has never openly admitted this, the evidence is overwelming. Rock chips are appearing on nearly all BMW Z3s and there really isn’t a solution to stopping them. While owners can’t win the war in the long run they can protect themselves and prolong the life of their paint using a product developed by 3M.

    3M makes a thin clear layer of protective film which can be applied directly over the paint. With this protective layer of clear skin the Z3 has additional protection against rock chips. It appears 3M decided to not market this new product directly to consumers but rather they offered the product to vendors that could make custom kits specifically made for certain vehicles. This is where X-Pel enterers the picture.

    X-Pel has kits made for the Z3 and M roadster that fit over the more vulnerable areas on the Z3. The front bumper and front 1/3 section of the hood are the most frequent places where the chips occur. The X-Pel kit covers all this area. In addition X-Pel also offers additional (optional) kits for the headlights, foglights, rearview mirrors and rear fender flares.

    Installing the kit requires patients and lots of water. The Z3 is watered down with soapy water so the thin layer can me float and move easily during the fitting process. A Squeegee is then used to press the film against the paint and remove the water from under the film. With the film in direct contact with the paint it adheres to the surface and stays in place. The film itself is not water tight so any remaining water trapped under the film eventually evaporates.

    Once installed, the thin layer can be seen on close inspection, but its difficult (you have to be looking for it). From a distance of four or more feet the kit can not be seen. On closer distances it is possible if you look for the edges. Occasionally you can catch it at the right angle and see the difference in refection. I stood over Larry’s car for several minutes trying to find that “just right” angle to show this to you in a picture. In the picture on the right you can see a flatter and slightly more yellow tint from the covered area. The yellow tint is really more of trick of the camera than an actual trait of the X-Pel kit. To the naked eye I never saw this yellow tint (sometimes cameras see things we don’t).

    X-Pel said that once applied, wax and wash the car the same as you usual. Except you should take a little more caution around the edges so you don’t get wax buildup on the leading edge of the kit. The expected life of the kit is four to five years.

    The Z3 club in Texas had a gathering in Dallas that didn’t involve driving but rather car care. The club invited X-Pel to come along and demonstrate the kit. By the time the event was over X-Pel had installed their kits on several Z3s and M roadster and each owner was pleased with their purchase.

    Swapping Mirrors

    Paint Chip Fixing Day at Rory’s House

    The Days Events

  • Gathering at Rory’s
  • Fixing Paint Chips
  • X-Pel
  • Swapping Mirrors
  • Boot Cover Swap
  • Chrome Front Grill
  • It all started with a casual conversation at the conclusion of the Texas River Run drive. I made a comment to Rory that we should have a non-driving Z3 get-together, maybe a Z3 fix-it day or something. One thing led to another and eventually we came up with a paint chip fixing day. We contacted a paint touch-up guy that Moritz BMW recommended, and a company that sells and installs invisible bras. Unfortunately, we had to limit the guest list because we could only handle so many Z3s at Rory’s house. Priority was given to Z3 owners that live in Dallas, however I bet there will be future events similar to this one so others can attend.

    This has got to be a record. Click on the picture to the right for a larger view of 11 BMW Z3s parked in one Z3 owner’s driveway. There were actually 12 Z3s at the event but Phil left in his Boston green Z3 before we took the picture. For fun, the Texas Z3 group would like to challenge other Z3 groups to take a picture with more Z3s in a residential (Z3 owner’s) driveway.

    Fixing Paint Chips

    Chrome Front Grill

    BMW Grill: still waiting for part number, suspect it will be roughly $40 for the pair of kidney grills
    Chrome tape: found at most auto parts stores, easy to install and costs under $10

    The Days Events

  • Gathering at Rory’s
  • Fixing Paint Chips
  • X-Pel
  • Swapping Mirrors
  • Boot Cover Swap
  • Chrome Front Grill
  • All 1996, 1997, 1998 and 1999 model year Z3s came with the same front kidney grills. The kidney shaped grills were surrounded in chrome with thin black slats running vertically in the middle. It was a great looking front grill but of course everything can be improved upon.

    Starting with the model year 2000 Z3 and M roadsters the front kidney grill is slightly different. The thin vertical slats in the middle of the grill are now trimmed in chrome. It’s a small change but it’s caught the eye of several Z3 owners. The good news is that the new kidney grill can be retro-fitted into older Z3s, however the new part number is not public knowledge at this point so we have to wait to order from BMW.

    Eileen found some thin chrome trim tape at her local autoparts store. After spending a few minutes cutting the tape to precise length, she simple stuck them on and the result looks great. For only a few dollars she made her front kidney grill just like the new grills. Who knows how long the chrome tape will last, but so far it is holding up quite well.

    Why is That Boot Cover so Hard to Install?

    The Days Events

  • Gathering at Rory’s
  • Fixing Paint Chips
  • X-Pel
  • Swapping Mirrors
  • Boot Cover Swap
  • Chrome Front Grill
  • 1st design: thinner leather was more flexible and easier to install
    2nd design: thicker and stiffer material than the 1st design possibly more durable but a pain to install
    3rd design: same thicker and stiffer material with redesigned tenax snaps

    Installing the boot cover on a 1996 or early model 1997 Z3 was a relatively easy job. However something happened during 1997 and BMW redesigned the boot cover with thicker and stiffer material. The new stiffer material makes it much harder to install. We confirmed this by swapping Eileen’s 1996 boot cover with my 1998 boot cover. I was able to install her boot cover in less than half the time it usually takes.

    We then started comparing the boot covers from the different Z3s that attended the event and noticed three different designs. Besides the flexible and stiff versions, we found a variation on the stiff version that had improved the tenax fastners. The front ones slide to make it slightly easier to install when compared to the other stiff material boot cover, but still harder than the original flexible material boot cover. If you have a Z3 with the stiffer boot cover, you may be interested in reading this article.

    Chrome Front Grill

    Swapping Z3 and M Roadster Rearview Mirrors

    Pros: Easy to uninstall and reinstall
    Cons: Expensive to purchase from BMW
    Cost: unknown (possibly free if you can find someone to swap with)
    The Days Events

  • Gathering at Rory’s
  • Fixing Paint Chips
  • X-Pel
  • Swapping Mirrors
  • Boot Cover Swap
  • Chrome Front Grill

  • The Z3 and the M roadster have different rear view mirrors. The M roadster mirror is bigger and sometimes gets in the way of taller drivers. The Z3 mirror is smaller but maybe isn’t as attractive as the M roadster mirror. The question was, could the two mirrors be swapped between cars.

    Turns out that all you need to do to remove the mirror as a counter clockwise, quarter turn (turn the entire mirror and its mount). We removed a Z3 and M roadster mirror and installed them in opposite vehicles in just a couple minutes.

    Boot Cover Swap

    Fixing a Paint Chip on Robert’s M Roadster

    Pros: Less noticeable than with no touchup paint, inexpensive
    Cons: Not “good as new”, still noticeable on close inspection
    Cost: $20 for entire car with roughly 10 chips needing work (Shane Reed @ 972-000-0000)
    The Days Events

  • Gathering at Rory’s
  • Fixing Paint Chips
  • X-Pel
  • Swapping Mirrors
  • Boot Cover Swap
  • Chrome Front Grill
  • After last years homecoming I picked up a real nasty rock chip on the hood of my M roadster. The rock that hit me caused a chip about 5mm wide and a pair of secondary chips that appear to have come from fragments of rock. Needless to say it was a big blemish that I wanted to get rid of.

    Shane Reed commented “boy that’s a nasty one”, and started to work on it. Using a fine paint brush and some thin paint that he mixed up, Shane applied a couple coats trying to fill in the chip.

    It was a definite improvement but Shane still thought he could do more. The paint he mixed up was a little off on the color. Turns out Arctic Silver has a touch of blue in it and the blue in the original paint really stood out next to the pure silver touch up paint.

    So Shane went back to his pickup (which doubles as a rolling paint shop) and added a touch of blue tint to the touch up paint. It was obvious that Shane had a keen eye for matching colors, a couple minutes later he had the right tint and went back to work.

    This time the paint color was a much better match. I’m not going to claim that it’s “like new” again but the improvement Shane made was definitely worth the money.

    Once the big chip was taken care of Shane scanned the car for other chips and touched them up as well. The lower part of the bumper had lots of litte chips and it appears Shane fixed them all. For those in the Dallas area I recommend Shane’s work if you are in need of touch up, contact information for him is below.

    Touch of Perfection (Shane Reed-Owner)

    Mobile # 214-695-1058

    Pager # 972-327-1393

    X-Pel