When it comes to the advancement of intercooling technologies, not much has changed for charged air conduits. Through the marvels of engineering, we have used liquid cooling power to create an intercooler that’s a quarter the size of an air-to-air unit while retaining the same, if not better, efficiency. However, we still need some good old-fashioned charge pipes to take the air from the turbo to the intake manifold. When it comes to the pipes equipped on the M3, the concept might be old-fashioned, yet their engineers managed to give them a new-age twist.

One of the first things you notice when opening the hood of your M3 or M4 is the general tidiness of the bay. Everything has its place and it’s not a mess of wiring or coolant lines running in every direction, which is no easy feat with the addition of an A2W system. The placement and design of the stock charge pipes are just as neat. From turbo to intercooler inlet, these pipes hug the block and head, sucking in their guts for the best clearance by the passenger-side intake. For a better look at BMW’s design, we opted for extracting these pipes.

The most notable design feature with these pipes is the unique shape they were assigned. Again, to confirm with BMW’s attention to detail and overall engine bay cleanliness, these pipes flatten out around their midsection to leave some room for the intake, but in such a way without sacrificing much in the name of flow. The most notable design feature with these pipes is the unique shape they were assigned. Again, to confirm with BMW’s attention to detail and overall engine bay cleanliness, these pipes flatten out around their midsection to leave some room for the intake, but in such a way without sacrificing much in the name of flow.

BMW wanted to make sure that these pipes weren’t going anywhere once installed. In addition to the securing brackets, each pipe has a specialized coupler that bolts the piping to the turbo in a precise orientation. Topside, these pipes couple to the intercooler with two short sections of rubber, but once we extract those, we found the inside of the piping is lined with aluminum to prevent deformation if overtightened.

Durability comes into question with the choice of construction. The pipes are almost entirely injection-molded plastic from head to toe. Granted, this is a popular method for intercooler pipe construction given the ease and frugality of producing thousands of these pipes at a time, but recent data has shown that these charge pipes have trouble under pressure.

Plenty of F8X owners have already suffered the results of a faulty charge pipe, which entails boost pressure hissing its way out of two possible fail points. The first of which is at the turbo-side coupler. The plastic welds fixing the coupler to the meat of the pipe aren’t always strong enough and completely sheer, filling the engine bay with all the boost that’s meant for the intake manifold. The second most common failure point is basically the entire rearmost pipe in general. This one tends to just split along most of the underside, again spilling precious pressure all over the engine bay.

Our engineer, Jason, is already on the case with a new design for charge pipes that can actually stand up to the pressure. After a thorough examination of the piping equipped from BMW’s factory, Jason elected to retain a few of the original features, but applied some updates in the name of durability and improving flow.

The plan is to ditch the plastic in favor of a full aluminum construction. The solid metal pipes mean no more splits across the pipe and saying goodbye to popping plastic welds. We will be retaining a factory-style connection to the turbos, and while the path to the intercooler will remain the same, our plan is to round out the pipes as much as possible to provide better airflow.

As seen above, the stock piping is a litany of bends necking to different diameters. It generally changes shape plenty of times. This means turbulence, crossflow, and loss of precious boost. Giving these pipes a more uniform and rounded shape will increase the interior volume of the piping, allowing the turbos a little more breathing room.

To ensure a precise fit, our piping retains the same mount to the S55’s turbos, this time TIG-welded to the piping to keep it in one piece as the turbos spool. The stronger metal construction will easily contain the stock boost pressures and keep the charged air contained once a tune is added.

In order to mitigate flow restrictions in the available space, our engineer had to get creative with the pipe construction. With the rear pipe, we were able to keep a more uniform, rounder shape from turbo to intercooler, allowing for a smoother flow. The front pipe, however, posed more of a challenge. Hugging the engine and in such close proximity to the intake, the rear pipe couldn’t adopt the same cylindrical profile due to spacing limitations.

Jason instead designed a fully cast section, which is welded in the center of the pipe. This construction allows for a perfect fit on the S55 without adding any unnecessary restrictions in the flow of charged air.

Even with our more uniform shape, increasing flow still poses a challenge. The lack of space to grow into is the main hurdle, so without hacking the stock engine bay to bits we maintained the status quo in terms of airflow from turbo to intercooler. A status flow, if you will.

The air-to-water intercooler is a system, and all the components need to play their part. The stock charge pipes were the weakest link in the mix, sometimes leaving the S55 short of breath. Our charge pipes are just the first improvement, so make sure to follow along for the unveiling of the rest of our F80 performance cooling suite.

When the F80s started showing up on the showroom floors, and more specifically in the driveways of their new owners, some were left scratching their heads inquiring about the “big silver box” prominently displayed in their engine bay. Thanks to the use of coolant to transfer heat from the charged intake air, the intercooler can be placed in line with the intake manifold, mitigating the extra lengths of hot- and cold-side piping. This small silver box has just about the same cooling power as an air-to-air intercooler three times the size.

To find out how, we did some exploratory surgery. We started by extracting the intercooler unit from our M3’s engine bay. Once removed from its perch on top of the S55, it’s even more apparent just how small the core is. Measuring in at 10.8”x 5.75” x 3”, the stock core is sporting a 186.3in^3 core volume. For comparison, the intercooler equipped with the N55 (aka the M3’s single-turbo’d little brother) has a core volume of 407in^3. Clearly there’s a reason BMW elected for this intercooling method, so we dug deeper.

The most apparent reason (as described in our heat exchanger post is that it’s much easier and more efficient to transfer heat to coolant thanks to the thermal conductivity of water. However, there’s a little more to this core than meets the eye, so we pried off the end tanks to take a look.

The tubes on the air side of this intercooler are packed with a dense fin design. Essentially, BMW is packing as much of the fin surface area from a traditional air-to-air intercooler inside of this core. By using a tight fin pitch combined with a standard offset fin design, the charged air has plenty of contact with the fins and effectively transfers the heat to the coolant.

BMW funneled the coolant’s flow through the intercooler in an interesting fashion. The inlet, or cold-side for the coolant, is injected at the top right corner of the core and across via a channel on top of the housing. From there it’s squeezed across the core via ducts just under the housing. Finally it trickles down and across to the outlet located on the bottom left side of the core.

BMW funneled the coolant’s flow through the intercooler in an interesting fashion. The inlet, or cold-side for the coolant, is injected at the top right corner of the core and across via a channel on top of the housing. From there it’s squeezed across the core via ducts just under the housing. Finally it trickles down and across to the outlet located on the bottom left side of the core.

While we had the intercooler disassembled, we took a closer look at the end tank design. For starters, they’re constructed from plastic, which is ideal for mass production but prone to leaks and cracks.

A peek inside the tanks is a visit to diverter city. When using this small of a core, it’s imperative that every single square millimeter is used. For that reason, BMW incorporated an internal diverter on both hot-side inlets to ensure an even spread of air flowing into the core, making full use of every densely packed fin. A feature we intend to keep in our design.

When we look inside the cold-side end tank, we see a similar story with how the air is straightened before entering the intake manifold. Combined with the general shape, these internal diverters are strategically placed to reduce the airflow’s turbulence as it passes into the throttle body to reduce pressure loss.

Done with Downsizing

While the future is about downsizing, we still see some room to grow when it comes to the F80’s air-to-water intercooler. Since the intercooler isn’t in the direct path of the airflow anymore, the size of the core can be a fraction of what it used to be. However, the old adage still rings true—bigger is better.

The first task on our to-do list is to give the core some extra muscle. The concept of transferring heat (though it’s to coolant in this scenario) is the same. The more condensed fin surface area we can cram in there, the better. Our design is going to bump the core size up to 241.5in^3, equating to a 29% increase in size over the stock unit.

Next item, coolant flow. There are two options when it comes to how we route the coolant through the core. The first is to retain the same path, which is to have it trickle through the channels via a duct on the top and bottom. The alternative would be to feed the coolant directly through the front and set up a dual pass system. It’s tough to determine the ideal coolant path at this stage, so in the name of science we plan on testing both. Make sure to check out the caption below for a more in-depth look on the dual pass core layout.

Final items are the end tanks. BMW laid an impressive foundation for us when it comes to the end tanks. Basically, there wasn’t much to improve on other than making the necessary adjustments to fit the larger core. Sure, these initial fitment prototypes are still plastic, but that’s just representative of the planned cast aluminum construction. Diverter city is not being evicted, but rather updated. Both the hot- and cold-side tanks will retain similar diverter designs in order to keep the charged air flowing smoothly through the system.

A Whole New Cool

With our assessment complete and the fitment confirmed, it was time for Jason to put his design plans in motion. Sure, the real beauty of this new intercooler design is the internal layout, but we couldn’t help ourselves when it came to the outward appearance as well.

The first noticeable feature is the cohesive design with the M’s engine bay. The stock unit is unsightly and sticks out like a sore thumb. While we wanted ours to be noticeable, we didn’t want it to clash. Drawing from BMW’s styling ques, our engineer carried over the same theme on the top and bottom plates of our intercooler, looking right at home in the bay.

The beauty is more than just skin deep. On top of expanding the core size, we had two different possible paths on the layout of internal coolant fins. We wanted to ensure that we were doing our due diligence determining which was best for the S55, so we made sure that we had one of our single pass, crossflow cores and fabricated a dual pass intercooler here in-house.

Both these core designs follow the paths laid out above, but with our new single pass design, we made sure to adjust the layout of the internal coolant fins in order for a more efficient passage of the liquid through the core. With the stock layout, the coolant is essentially playing a game of Plinko to squeeze from one side to the other. This means of coolant passage could potentially stay in the core too long and start transferring the heat back to the charged air. By creating a more streamlined path through the core, we’re establishing an environment for more consistent and effective cooling.

The coolant side of the core is only half of the story. Ensuring the air side of the fins are up to snuff is just as important. The stock core uses a tightly packed offset fin design, which is the same formula that we also used, but the larger core means that we could make some adjustments. More space allowed us to still use the offset fin layout, but with a slightly looser fin pitch, all while increasing the volume of fins. These improvements combined mean a 16% increase in the airflow through the core. This stat that will come in handy once we get to the dyno.

Speaking of airflow, this new core would practically be worthless without the means of shepherding the charged air through it. Since BMW already laid a sturdy foundation, there wasn’t too much Jason needed to change for our end tanks. Updates were needed nonetheless. For starters, plastic is out and cast aluminum is in. This new manufacturing process means a much more reliable air passage to and from the core. The main update in shape comes from the intercooler’s outlet. We gave the interior of this end tank a bit more of a curve for a smoother flow of air into the intake manifold, which contributes to the improved flow.

Group Effort

In case you haven’t already figured it out, air-to-water is a team sport. The intercooler is reliant on the heat exchanger to dissipate the collected heat in order to properly cool the charged air. For that reason, we were primarily interested in pitting the results of our system against the stock layout during the test. In addition, we also know that most owners looking to upgrade their intercooling system are doing so because of a tune, so we ran all our tests with a Stage 1 map to compare the systems.

We are primarily monitoring three main attributes to determine the effectiveness of each system—power, intercooler coolant temperatures, and the intake air temperature. In order to capture this data, we split the testing into three different sections which help pinpoint each set of data more accurately.

First up, the intercooler coolant temperature. This figure is the foundation of the results, meaning that by improving the cooling capacity there’s also a positive effect on IAT and power. This also specifically points to how well the heat exchanger performs within the system. To collect this data, we performed a load test with our M3 on the Dynapacks in which the vehicle is put into 4^th gear, and then held at 4000RPM for 30 seconds. This puts the M3 under a heavy load to make sure that the intercooling system is working its hardest throughout the test.

Through this two graph we were able to decipher the heat exchanger’s performance as well as the total cooling power of the system. First, by comparing the data between the inlet and outlet at the 70 second mark, we saw a 25°F drop in coolant temperature across the core. That’s 6°F better than the stock unit. With just our heat exchanger installed, we were able to lower the global system coolant temperatures by 10°F and an additional 3°F once our intercooler was in the mix. 10-13°F might not sound like much, but with the coolant temperatures consistently lowered, it means for more efficient heat transfer from the charged air.

With the coolant temperatures dropping, we were able to see the effect on the air passing through the intercooler. We also measured the temperature of the air entering the intake manifold both after the stock and our intercooler during the load tests. From the same 70 second mark in the test, we recorded a 12°F drop in the intake air temperature after the installation of our intercooler.

The missing piece to this puzzle is: What do all these improvements lead up to? Sure, extra power is one thing, but the better and more consistent cooling for your Bimmer’s intercooler system means a solid platform for even more modifications. But yeah, the power too.

Collecting a consistent power figure on the M3 proved to be a little tricky. Essentially, the horsepower and torque numbers shifted depending on the heat soak in the system, so there were inevitably some outliers. Sure, we could have just plopped the fattest horsepower gain here and called it a day, but we’re not about cooking the books. Instead, we recorded our power figures over a series of six consecutive dyno pulls, similar to one of our heat soak tests, and averaged them together. This way we’re collecting not only a more consistent set of data, but also simulating a real-world result. We were able to record an average 3–5 gain in horsepower and 2–10 boost in torque on top of the gains from the tune, with a peak of 31 horses and 10 ft-lb. across the series of runs. 

We performed all these tests side by side with our dual pass core design, as well collecting similar results in each experiment. We ultimately decided to move forward with the single pass core design since it allowed for more internal fin volume, and we saw an improved flow equating to more potential heat rejection.

Perfection Powered

When it comes to sports sedans, the M3 is as close as you can get to the perfect balance between carving corners and soaking up the highway. BMW did have a few shortcomings when it came to the latest iteration of the market’s benchmark, but we here at Mishimoto made sure to reinforce the weak spots so the F80 could keep its title as the Ultimate Driving Machine.

Why does the transmission temperature on the F80’s DCT matter? Simply put, the excess heat can wear the oil in the transmission prematurely, which diminishes the oil’s lubrication properties. The DCT is, in essence, a clever combination of an automatic and manual transmission. However, instead of a torque converter, there is a pair of clutches that split duties between the gear ratios, most commonly split between odd and even gears. These clutches are commonly wet clutch packs and utilize oil to cool the clutches, given the immense friction. The clutches continually switching gears, not to mention the constant gear meshing between the two gear sets, already generates plenty of heat, but a spirited track day on top of that could lead to issues down the line.

This isn’t BMW’s first rodeo, though, and their engineers already equipped the DCT-optioned M’s with liquid-to-air cooler for keeping the transmission fluid temperatures in check. BMW incorporated a single-pass cooler that measures in at 21.75x3x1”, giving it an adequate core volume to contend with most daily driving duties. They also made sure to utilize hard lines for a secure connection to the transmission lines and implement the use of internal fins to promote more efficient heat transfer.

We still saw room to grow, though, and started our design process with a full 3D scan of the stock unit with the help of our Faro Design Scanarm. With the scan completed, Jason got straight to work on our new design. There was limited space to expand into; however, Jason was still able to add an inch to the height and bumping out the thickness to 1.25” which equates to a 42% increase in core volume over the stock unit. Also, Jason made adjustments to the external fin design, adding three additional rows, that put our cooler at a 69% increase in external fin surface area for improved heat dissipation.

Our new design is more than just skin deep as well. We were able to carry over the use of internal fins that promote increased heat transfer to the external fins. We also adjusted the layout of our inlet and outlet to accommodate a dual-pass flow through the core while retaining a direct fit on your Bimmer. With these features combined, we were able to record a 15% increase in heat rejection and improved heat regulation over the stock unit during our bench testing.

While BMW already knew that transmission temperature regulation was imperative, they were still aiming for a more common cooling approach. With our cooler, you’ll spend less time worrying about transmission temperatures in your M, and more time just enjoying the Ultimate Driving Machine.