It’s no secret that the engineers at BMW strive to make each level of their M lineup the top tier in each segment. When it comes to the F80 and F82, the twin-turbocharged and liquid-intercooled grunt of the S55 coupled with the agility of the 3-series chassis is a killer combination that rockets these Bimmers to the top of the class. While the duo works on paper, in everyday use there is one aspect that does, quite literally, crack under the pressure—the charge pipes.
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.
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