|Pros:||Performance, Exhaust Sound|
|Cons:||Not a “Do It Yourself” Install|
BabyZ wanted to get her exhaust modified for two basic reasons. One for increased performance and two, so she would sound like the high performance sports car she is. Three things hindered performance of the OEM exhaust system. First of all the OEM unit is very heavy (approximately 30 lbs.). The reason it is so heavy is that there is a lot of baffle material in it to make the engine very quiet. This results in the second performance problem that this material creates a large backpressure that reduces engine horsepower. The third problem is an additional source of backpressure in the exhaust pipe. Where the pipe goes under the rear axle it has a large kink put in it to apparently increase the clearance from what look to be quite ample with a full diameter pipe to an even greater clearance.
The kink is not easily seen in this picture of the OEM system as it is right behind the massive hangar and in front of the shinny resonator (close-up of this kink follows in a bit). The second basic desire was to hear the engine. BabyZ didn’t like being a wolf in sheep’s clothing. She’s bad and doesn’t mind anyone knowing it!
Well we have a pretty good idea why BabyZ wants new pipes now, so the next problem is deciding what to put on instead. The first requirement was the system had to be all stainless like the OEM one. In some areas this may not be as important as it was to me but with the rain, humidity and chemicals present in Houston, this was a must. This eliminated the Remus as it is not stainless, a nice sounding unit for sure, but not stainless. The stainless units available were Supersprint, B&B and Borla. With Supersprint and B&B you can get a cat back bolt on system that uses the OEM hangars while the Borla is a weld up modular system. If you want to do this all yourself, and assuming you aren’t a stainless welder, you would not be able to do the Borla. This however may not be a total disadvantage if you don’t mind letting a muffler shop in on the fun. Two reasons balance out the ability to do it yourself are the cost of the system and the sound. Borla is cheaper even after the shop install and gives more sound with a deeper tone than either the Supersprint or B&B (IMHO). Based on the extremely detailed research done by theBaba, where he determined that the Borla did make a muffler (PN 40651) that fit the system and satisfied all BMW requirements (even though they did not list the Z3 on their application list) and testing out his fine ride, Hans, this was the system decided on for BabyZ. Another advantage for BabyZ is that she could keep the resonator which was felt desirable given her automatic tranny (of course you can drop the resonator for a manual if you like).
In the photo of the OEM and Borla mufflers on the ground the difference in size is apparent, but what you see is only part of the story. The weight difference is incredible with Borla weighing in at well under half of the OEM. The smaller size should also help with heat dissipation and reduce the heat exposure to the floor of the trunk and the battery. You can also see that the inlet and outlet to the muffler line up around the centerline of the muffler exactly at the same points as the OEM so the tips will line up with the bumper cut out without any modification.
This is a close up of the infamous “kink”. It actually is more of a smash. The pipe looses fully half of its diameter to go under the rear axle and meet the BMW engineers specified clearance. This smashed pipe is eliminated in BabyZ’s new pipe. In over 2 years of operation since installing the Borla with a full diameter pipe I do not see any indication on the pipe that it has ever been hit by the axle. This includes street, cross-country, track and autocross driving.
This shows the full diameter pipe going under the axle and you can hopefully see that there is plenty of clearance. Also, a new hanger was used on the pipe and attached to the original mounting point. (Note. The second OEM mounting point on the left of the muffler was also used but the third on the right rear of the muffler was not used.)
The shop foreman fabricated the stainless steel “Y” for the dual tips. It was quite a battle to see who would get to install the muffler on BabyZ, I guess this proves that “Rank Has It’s Privileges”. The tips are Borla Turbo Intercooled (PN 20102) and are also stainless steel.
The tips are staggered at the ends to follow the contour of the bumper. This is a personal preference as theBaba and others have theirs straight across and both ways look fine. Another thing to note is that the tips are not positioned on the centerline of the opening in the bumper cover but are moved toward the right side of the opening. This was done to give the maximum room for the tips to move left as the exhaust pipe warms up and expands. This will prevent the tips from touching and melting the surrounding bumper material. The tips are also positioned close together to further maximize the safe area for tip movement.
The finished product is and all stainless steel system with the resonator left in place to compensate for the low rpm preference of the automatic transmission. The Borla is the easiest available system to customize this way and can be installed with or without the resonator (true cat back) as per your preference.
Borla is also the loudest of the systems and depending on your desires this is either a positive or a negative. One drawback is that it is the loudest at 2300 to 2800 rpm’s. This equates to 50 to 60 mph and can resonate quite a bit with the top up. There are two other things wrong with that scenario in the first place; i.e. why is the top up and what are you doing going less than 60mph for any way, so it isn’t much of a consideration for me.
Installation of the Borla resulted in a nice performance boost that was most noticeable in the low rpm range especially in accelerating. The Borla was the first performance upgrade on BabyZ so there were no other mods that could have interfered with the effect of the exhaust upgrade. Since this time the chip has been upgraded with Dinan programming and the airbox has been “Fogged”. Each of these upgrades had an additional effect and I recommend that the full trifecta be done to get the maximum effect from all of the upgrades. One interesting side effect of the addition of the airbox upgrade is that the tone of the exhaust changed and a particular resonate tone was eliminated. I take this as an indication that a definite restriction in airflow was eliminated with this upgrade and that the exhaust was happy to accommodate the additional airflow.
One other benefit is that you won’t need “no stinkin stereo upgrades” when you are listening to the sweet Z3 engine music played through a Borla.
Cost of the muffler and tips is about $300. Installation, including all the needed pipe was $100 and it took about an hour and a half even with a substantial amount of discussion and picture taking. . The Borla is made of T-304 stainless and has a one million mile warranty. Borla’s website is at http://www.borla.com.
Discuss this article and other Performance upgrades in the
///MZ3.Net discussion forum.
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.
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).
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.
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.
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).
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.