Supersprint Exhaust for the 2.8 Z3

Pros: Better Performance, Great Sound, Stainless Steel
Cons: Expensive, Installation
Cost: $614 (from BMP Design)
$563 Straight Tips with free shipping (from HMS)
$649 DTM Tips with free shipping (from HMS)

In the never ending quest to find more power and otherwise tinker with my car, I decided to put a new Supersprint catalyst-back (cat-back) exhaust on my beloved BMW Z3. I have a ’97 model with the M52 2.8 liter engine.

The upgrade had three desired goals/expectations

I was looking to improve the sound of the exhaust. The stock exhaust didn’t sound “bad”, it was just too quiet for my taste. I had previously heard other 2.8 liter Z3s with the Supersprint exhaust so I was quite confident that I would be pleased with the sound.

I was hoping to improve performance of the Z3 as well. This goal was questionable, several had speculated that there wouldn’t be an improvement in performance. However there were even more saying there would be. In order to satisfy my own curiosity I decided to do before and after dynamometer (dyno) runs on the car to measure before and after rear wheel horsepower and torque.

The final expectation was purely cosmetic. I had already added chrome tips to the stock 2.8 exhaust (picture above) but after seeing the larger turned up DTM tips available on the Supersprint exhaust I decided I liked the looks of them much better (right picture).

With these goals in mind I enlisted the help of Robert Leidy, who had already found a reputable dyno shop when he measured the power output from his M roadster. Since Robert and the dyno shop (Alamo Autosports) were both located in the greater Dallas/Fort Worth, Texas (DFW) area, and I was located in Houston, there was a bit of a logistical problem. Answer: Roadtrip!

To ensure a proper installation, Larry Nissen from Moritz BMW in Arlington was invited. To ensure accurate dyno tests the following “recommended” process was used. We first backed the car onto Alamo’s dyno rack to get a baseline HP for the car. We then used the very same dyno lift to install the supersprint exhaust. Once the exhaust was installed the car was then re-dynoed to measure the change.

Installation

Prior to installing the Supersprint exhaust, three “before” or baseline dyno tests were preformed. The results of those test will be compared to the results from the “after” dyno tests in the next part of this article. But for now let me explain the installation process that took place between the before and after dyno tests.

The keen eye will notice that the pictures on this page are from two different vehicles. Prior to my installation, another Z3 owner had installed a Supersprint exhaust on his Z3 and Robert was there to take pictures of that installation as well. The only difference between the two Supersprint exhausts were the type of exhaust tips. Chris got the straight tips and I got the turned up or DTM style tips. Since the type of tips on the end of the exhaust have very little impact on installation the two sets of pictures could be used together.

The first step was to remove the stock exhaust, problem was we had just completed the first set of dyno tests so the stock exhaust was hot. After the stock exhaust cooled down to a point where we were able to hold it (15 minutes) we were able to remove it.

The exhaust is held in place in four places (pictures below). The first (front most) connection is where the exhaust bolts onto the flange of the catalytic converter via two 2 13mm nuts and bolts. The middle connection is actually just a safety/backup connection, but it uses a rubber belt (attached to the vehicle) around an additional bracket (attached to the exhaust) to catch the exhaust if the rear mounts fail.

Towards the rear bumper, two additional rubber rings support and attach the rear of the exhaust to the vehicle. In order to remove them we sprayed the rubber muffler hangers with lubricant and then popped them loose using a pry-bar. The actual order we used in removing the exhaust was to loosen the front bolts, unbolt/remove the middle bracket. Then with someone holding the front of the exhaust, the rear connections were worked loose. With a person holding either end the removal was easily accomplished, however it would have been rather difficult with only one person. trying to juggle both ends.

After removing the stock exhaust it was time to unpack the Supersprint exhaust. I purchased this exhaust from BMP, it came very well packaged, the entire exhaust was wrapped in thick shrink wrap with additional padding covering the exhaust tips. Not sure if this is something BMP does or if all Supersprint exhausts come this way. The packaging provided a very effective protective layer over the exhaust, however the shrink-wrap was so tight one of the support brackets was bent. We didn’t realize this at the time, but later it was easy to fix by just bending the support back to its normal position, the catch of course being that you won’t know what the “normal” position is until you’ve got the exhaust installed and you’re trying to put the rubber hangers on.

There is one important part I should point out, you better get a friend to carry the new and old exhaust for you. The exhaust is rather large and does not fit in the trunk (not even close). You could carry the new exhaust up front with you but the used/stock exhaust will be very dirty. For this installation Nancy carried my exhaust along with Alan’s two exhausts in her SUV. Once the stock exhausts were removed we wrapped them in trash bags and duct tape for the drive home.

Comparing the stock and Supersprint exhaust side by side was interesting. The Supersprint exhaust looked quite handsome with its black-crackle finish and polished stainless steel tips. It also looked much more svelte and linear than the stock exhaust. The stock exhaust had 4 diameter changes in just the piping alone. The resonator and the garbage-can-sized muffler looked like something off of a truck when compared with the Supersprint. There was a brief moment where I thought BMP had shipped me the wrong exhaust. The muffler part of the exhaust was smaller so the rear support arms were longer (to make up the difference). But what concerned me was how much different the connection from the catalytic converter to the muffler was. The Supersprint still had the crimp in the exhaust but the path seemed much straighter. However my concerns of receiving the wrong exhaust were removed when we stacked the two exhausts on top of each other and noticed the mounting locations were the same.

Mounting the new exhaust was a definite two-man job. The “safety hanger” was reinserted into the rubber hanger/bracket, and the flange-end of the exhaust was fitted to the catalytic converter, loosely fitting the nuts. We then re-popped the muffler hangers on to the Supersprint, and VOILA!, it didn’t fit. We stepped back to analyze the situation and found immediately that the hanger brackets on the Supersprint had been bent somewhere along its route from Italy to Texas. Using the biggest pair of channel-locks we could find, we adjusted the brackets to proper alignment, and VOILA!, it still didn’t fit.

We has been warned by other Z3 exhaust upgraders that the tight fit of the exhaust tail pipes had previously led to some bumper trim scarring/melting. Because of this warning we were paying very close attention to how the tips fit in the cutout. Ahead of time we were warned that the exhaust tips will move towards the drivers side of the cutout when the exhaust gets hot and back towards the passenger side when it cools back down. So our goal was to get the exhaust tips to hang towards the passenger side of the cutout as much as possible (exhaust was cold as we were mounting it).

The problem we ran into was after installing the exhaust we noticed the tips were already off center towards the drivers side. We knew that this was going to be a problem because once the exhaust got hot it would push even further towards the drivers side and probably scar/melt the bumper trim. Further analysis indicated that the “safety hanger” on the Supersprint was too far to the passenger side of the car. After inspecting how the bracket worked we determined that the sides of the bracket serve very little purpose because the support loop uses the top of the bracket. We were also told that this bracket is just a backup bracket in case the rear ones fail.

For a brief moment we considered removing it all together, but then we thought of a better plan. We decided to modify the safety bracket, since it appeared cheaper to replace than the exhaust if we screwed it up (Supersprint has been informed of the problem and is investigating a solution). The bracket pictured to the left is after the modification (compare it to one of the pictures at the top of this page and you will noticed the removed metal). The fine folks at Alamo ground off one side of the bracket, and after we re-installed everything the exhaust was no longer being pushed against the drivers side of the rear bumper apron.

All that remained was to fine-tune placement of the tips within the rear bumper apron. This was accomplished using the aforementioned massive channel-lock pliers to tweak the muffler hanger brackets. We aligned the exhaust to “dress to the right” when cold, as 2.8 Supersprint exhausts are known to shift left about one-half inch at operating temperatures. It looked fantastic.

Update: Supersprint is modifying all current and future 2.8 Z3 exhaust systems to correct for the safety bracket misalignment. Supersprint is also adding side-to-side adjustable hangers to allow for precise fitting of the exhaust tips in the cutout.

Performance

Now that the Supersprint exhaust was installed, it was time to dyno again. When we first ran the car on the dyno, (pre-exhaust) I was nervous to say the least. My car already had the Dinan High Flow Cold Air Intake System and Dinan ECU upgrade (not really a “chip” anymore) and I had heard ad-nauseum about how the adaptive nature of the OBD II ECU software would show no power gains no matter what.

Running your car on a dyno is one of those surreal experiences you have to do once in your life. On a lift dyno, your car is roughly four feet in the air strapped to the lift, going 70+ mph The image of the car shooting off the lift keeps popping up in one’s mind. Anyway, we do three baseline runs. They are all pretty consistent, with the best being 167.6 hp and 175.5 ft lbs of torque. Remember that this it rear-wheel horsepower and torque, not the crankshaft horsepower and torque as quoted by the factory.

After we installed the Supersprint we fired up the engine to warm it up, and it sounded fantastic, too. Stock, the car just didn’t have a sporty-enough sound. With the addition of the Dinan Intake and ECU upgrade, it had a very feral howl, but only on wide-open throttle. The Supersprint exhaust added a “bass track” to the sound, sounding it out nicely. Now, full throttle applications combine the howl with a deep growl, making for a formidable sounding beast.

Below is an amusing animated picture Robert created from a couple still pictures his camcorder recorded. The first frame is from the “before” dyno test with the stock exhaust. The second frame is hours later from the “after” dyno test with the Supersprint exhaust (with turned up DTM style exhaust tips). I’m sure the angle of the exhaust tips had more to do with it than the amount of exhaust, but notice the Dynojet banner in the background. Now that’s what I call a free flowing exhaust 🙂

Once we warmed up the car, it was time to dyno. The sound of the car running up to over 70 mph in what was essentially a one-car garage was a sound not easily forgotten. One alarming note, though, was the plumes of smoke emanating from the rear of the car. Turns out that it was the exhaust burning off coatings, grease, and other contaminants. It had a mighty stench as well, which I was told would linger for about 500 miles. I was glad I had a long roadtrip home.

Once again, we do three runs, and they are again very consistent. This time the best one is 171.7 hp and 181.1 ft lbs of torque. Click on the small portion of the graph to the right to see the full size before and after comparison of the torque curve. At the peak torque values, the Supersprint exhaust gained 5.6 ft/lbs of torque. Looking at the entire RPM torque curve and measuring the differences every 50 RPM the Supersprint exhaust averages a gain of 4.3 ft/lbs of torque between 2000 and 6200 RPM.

It would appear that this is an apples and oranges comparison, and it is somewhat. However, there are correction factors, and the one we’ll use here has been ascribed to a well known Utah-based chip tuner, but I can’t confirm that origin. This correction factor to convert rear wheel HP to crank HP is 1.21, or about a 17.2% loss. Given that, my numbers would work out as follows using the equation RW * CF = C, where RW is rear wheel HP or Torque, CF is the above correction factor, and C is the crank HP or Torque.

Stock 1997 2.8 – factory specs

189 HP

156.2 HP – converted to rear wheel

203 ft-lbs Torque

167.8 ft-lbs Torque – converted to rear wheel

With Chip & Intake:

167.6 * 1.21 = 202.8 HP

175.5 * 1.21 = 212.4 ft-lbs Torque

Chip & Intake gain over stock:

13.8 HP – estimated @ crank

11.4 HP – estimated @ rear wheel

9.4 ft-lbs Torque – estimated @ crank

7.7 ft-lbs Torque – estimated @ rear wheel

With Chip, Intake & Exhaust:

172.6 * 1.21 = 208.9 HP – estimated @ crank

181.1 * 1.21 = 219.1 ft-lbs Torque – estimated @ crank

Chip, Intake & Exhaust gain over stock:

19.9 HP – estimated @ crank

16.4 HP – estimated @ rear wheel

16.1 ft-lbs Torque – estimated @ crank

13.2 ft-lbs Torque – estimated @ rear wheel

Chip, Intake & Exhaust gain over Chip & Intake:

6.1 HP – estimated @ crank

5.0 HP – measured @ rear wheel

6.8 ft-lbs Torque – estimated @ crank

5.6 ft-lbs Torque – measured @ rear wheel

So what does this tell us? Well, if we believe in rear wheel measurements only, I got a 5 HP, 5.9 ft-lbs, increase in overall power. Examining the dyno curves, this really makes itself known over the 3000 – 5500 rpm range. I am happy, and I can feel a difference.

Sound

Bryan: One month after install

Living with the exhaust has been a pleasant experience. I had to first get over the feeling that someone was following me, as I wasn’t used to the subtle tone of the exhaust coming from the rear at all RMPs. Next, I was worried about the much larger exhaust melting the rear bumper fascia. I’ve seen some exhaust applications that have eaten holes in the fascia, but that hasn’t been a real problem. There has been a little scorching on the inside lips of both sides of the fascia, but nothing to be concerned about. One very unexpected benefit is that my gas mileage has increased by 1-2 miles per gallon. Bottom line: would I do it again? Yes. What would I change? the safety bracket

Chris: 1 month after install

Chris Bull checked the rear apron around his Supersprint exhaust installation with straight tips and reports that no melting or scarring has taken place. He is VERY pleased with the upgrade and highly recommends the Supersprint exhaust to other 2.8 Z3 owners.

Spence: 1 month after install

Chuck Spensor checked the rear apron around his Supersprint exhaust installation with DTM style tips and reports that there is some melting on the drivers side. However the scarred area is not very noticeable and the exhaust tip hides most of the damage. He is VERY pleased with the upgrade and highly recommends the Supersprint exhaust to other 2.8 Z3 owners.

Update from Supersprint:

There are two different 2.8 Z3 exhausts, one for the ’99 on Z3 2.8 coupe and roadster, and one for the ’98 and before Z3 2.8 roadster. The part number for the 99 is 78.67.06 or 78.67.66 (I guess one is straight tips and the other is dtm–don’t know which is which). Supersprint experimented with a ’99 Z3 2.8 coupe and moved the center bracket approximately 6-8 mm towards the driver’s side of the car to give it a perfect fit. They did many runs to get the exhaust up to temperature and verified that it did not come into contact with the apron even under hard cornering. One point to note is that the ’99 models apparently have a bigger cutout in the rear apron than the ones before that. For the ’98 and before 2.8 roadster, Supersprint is modifying all current and future stock to have a side-to-side adjustable hanger to allow for precise fitting.