Most single turbo build content online covers the result. The dyno number. The final pull. The reaction when the number comes up on the screen.
What most content does not cover is everything between day one and that dyno pull. The specific tools. The specific bolts. The specific moments where doing something wrong means disassembling what you just assembled and starting over. The parts that interact with the 4N Motorsport kit that nobody mentions in the kit instructions but that matter enormously to whether the build goes smoothly or becomes a nightmare.
We built an F82 M4 from stock S55 twin turbos to a fully running 4N Motorsport single turbo setup and documented every single day. Here is the complete breakdown of what happened on each day of the build, what it required, what we learned, and what the car became by the end of it.
Day One, Understanding What This Build Actually Involves
Before a single bolt was touched on the F82 M4, the 4N Motorsport kit went on the bench. This is the first lesson of any serious single turbo conversion. Understand what you are working with before the car is apart.
The 4N Motorsport bottom mount single turbo kit is built around a Borg Warner turbocharger that the BMW performance community already knows by reputation. The manifold is a tubular twin scroll equal length design, which means the runners are engineered to bring exhaust gases from each cylinder to the turbocharger as efficiently as possible. Equal length runner design reduces turbo lag by ensuring consistent exhaust pulse energy reaching the turbine wheel. It is also a significant part of why the S55 with the 4N Motorsport kit sounds so distinctly different from any stock twin turbo M3 or M4.
The goal for this build was a complete personality change. Not just more power. A different kind of power delivery. Replacing the instant, linear character of the stock S55 twin turbos with the build and pull to redline experience of a large single turbocharger. A car that sounds different, accelerates differently, and creates a different experience at every point in the power band.
Day one was stock turbo removal. And the S55 engine bay made sure nobody forgot how serious this conversion actually is.
The S55 engine bay is legitimately one of the most tightly packaged engine environments in modern BMW history. Two turbos, an intercooler, extensive plumbing, and a complete electrical harness all compressed into a space that leaves almost no room to work. Getting the stock twin turbos out requires specific tools and specific sequences.
Tools required for the Day One teardown: Starting from the top of the engine bay, an E12 socket removes the brace. Moving further in, an E16 socket handles the next brace. The charge pipes connect to the charge cooler and turbos with 6mm clamps on stock setups, though this can vary if aftermarket charge pipes are already installed. The intake pipes have 8mm clamps and a 10mm bolt securing the intake pipe itself.
Once the intake and charge pipes are cleared, the turbos themselves become accessible but only just. The O2 sensors unplug first. The passenger wheel comes off to provide access to the underside of the engine where the downpipe and turbo connections are made. The motor mount and post mount have to come off to create the clearance needed to extract the turbos from the engine bay. The post mount bolts are E14. The motor mount bolts are E12.
The actual turbo removal bolts on the manifold are reached only after all of that is cleared. And they are reached by feel in many cases. Scrapes, tight angles, and patience. By the end of day one, one turbo was out. The second turbo was waiting for day two.
Watch Day One of the 4N Motorsport M4 Build:
Day Two, The 4N Motorsport Kit Goes In
Day two started with the second stock turbo coming out and ended with the 4N Motorsport single turbo kit installed on the S55. This was the transformation day. The day the car stopped being a stock M4 and started becoming something else.
Bench preparation before installation:
Everything possible was done on the bench before the 4N Motorsport kit went near the car. The cold side housing of the turbocharger was removed and stored safely. The turbine fins inside the compressor housing are the most vulnerable part of the entire assembly during installation. Nothing can touch them and there is no protection once the housing is off. Damaging those fins means buying another turbo.
The exhaust studs on the S55 were removed before the 4N Motorsport manifold went in. This is not in the kit instructions and it is the step that makes the difference between fitting the manifold easily and fighting it for an hour. With the studs out, the manifold clears the head properly and locates correctly without the frustration of working around hardware that should not be there during installation.
Installing the 4N Motorsport manifold:
The tubular twin scroll manifold from 4N Motorsport is visually impressive in person. The welds are clean. The runners are smooth. It is clearly engineered rather than fabricated by whatever process produces the minimum acceptable result. Getting it into position in the S55 engine bay requires patience and the right approach angle.
Mounting the turbocharger:
The 4N Motorsport Borg Warner turbo is large. Anyone who has only seen stock BMW turbos in person will be immediately struck by the size difference. Maneuvering it into position requires two people, careful attention to the turbine fins at all times, and a steady hand placing it correctly on the manifold without allowing anything to contact the compressor wheel.
The most critical step of the entire 4N Motorsport installation, the wastegate actuator rod:
This is the step that catches people out and forces a disassembly if it is missed. The 4N Motorsport kit uses a different wastegate actuator setup than the stock S55 twin turbo system. A replacement actuator rod comes with the kit and must be correctly positioned before the cold side housing is installed on the turbo.
When fitting the cold side housing onto the hot side, the actuator rod has to be aligned with the hole in the wastegate on the hot side. This alignment cannot be checked after the housing is on. If the housing goes on without the rod correctly positioned, the housing comes back off. Check the rod position every time, before the housing is seated.
Oil and coolant connections:
The oil feed line to the top of the 4N Motorsport turbocharger is tightened with a 14mm wrench. The blockoff ports for the now-removed twin turbo drain locations have to be properly addressed to prevent oil management issues after the build is running.
Maintenance items addressed simultaneously:
On this build, the valve cover, valve cover gasket, ignition coils, and upgraded injectors were all addressed during the same teardown. If these items are due on an S55 that is being converted with the 4N Motorsport kit, doing them during the build avoids having to partially disassemble the kit again shortly after. The spark plugs were gapped at 0.022 inches per the tuner's specification for the initial tune on this setup.
Day Three, Fuel System, Port Injection, and Downpipe
Day three was the day that separated this build from a basic single turbo conversion. The 4N Motorsport kit handles the turbocharger and manifold side of the equation. Day three was about making sure the fuel system could support what that turbo was going to ask for.
Motive Port Injection System:
The Motive Reflex port injection system adds a secondary set of injectors that supplement the stock direct injection system under high boost and high power demand. At the power levels this 4N Motorsport build was targeting, the stock direct injection system alone is not sufficient to deliver the fuel the engine needs. Port injection fills that gap.
Installing the Motive port injection plate requires removing the intake manifold first. The manifold is held on by 11mm bolts and several connectors and comes off without excessive drama once everything is disconnected. The port injection plate uses extended studs, which require removing the original intake manifold studs with an E7 socket before the new extended studs can be installed.
The critical installation note for the port injection fuel line is that the top nut needs to be secured without overtightening, since there is an O-ring in that connection that needs to seal correctly. The push-down fitting that connects to the stock fuel line running from the injector rail must be confirmed seated and locked before the charge cooler and intake manifold go back on. Finding out after reassembly that this connection is not secure means taking everything back off.
The J-pipe O-ring swap, a critical step nobody talks about:
Before the J-pipe was installed, the O-ring from the original J-pipe was transferred to the new unit. This O-ring is small enough that it is easy to overlook and common enough to forget that it is not included with replacement J-pipes. Missing this O-ring creates an air leak at the boost pipe connection that shows up immediately under boost. On a fresh build that took days to complete, finding a boost leak from a forgotten O-ring is exactly the kind of setback that is entirely avoidable.
Wastegate linkage adjustment:
Before the downpipe went on, the wastegate linkage was adjusted using a laptop connected to the tuner's software. This adjustment calibrates how the 4N Motorsport kit's wastegate responds to boost targets. Skipping this step and driving the car without proper wastegate calibration produces inconsistent boost control and defeats the purpose of the 4N Motorsport kit's engineered design.
Day Four, The Dyno
Day four was the only day that mattered for the rest of the internet and the day that confirmed everything that happened on days one through three was done correctly.
The F82 M4 with the 4N Motorsport single turbo kit drove an hour to the dyno. It came off the dyno producing 710 wheel horsepower.
The first pull of the day was 667 wheel horsepower before serious tuning work had been completed. That first pull number tells you more about the 4N Motorsport kit's capability than the final number does. Starting at 667 before the tune is dialed in is a statement about the hardware.
Through the tuning session with Steve from Wedge Performance, the car climbed progressively. The data comparison between the first and last pulls showed the specific improvement the tuning session produced. At 5,500 RPM, the car improved from 564 horsepower on the first pull to 682 horsepower by the final pull. That mid-range gain is exactly what proper tuning does for a 4N Motorsport equipped S55 and is the reason the tuning component of this build matters as much as the hardware itself.
The final number of the day was 710 wheel horsepower. The build goal was 700. The car cleared it.
The tuner's assessment at the end of the session was that the car would still feel the boost build differently than the owner was accustomed to from the stock twin turbo setup. The power would arrive after a moment of building rather than the immediate response of the smaller stock turbos. When it arrived, it would arrive completely.
What the 4N Motorsport Build Actually Costs
Builds like this are not inexpensive and being clear about that serves everyone better than vague references to the investment involved.
The 4N Motorsport single turbo kit itself is a significant purchase before any of the supporting components are considered. The port injection system, upgraded injectors, ignition coils, valve cover, valve cover gasket, J-pipe, downpipe, and ethanol-related fuel system components are all additional expenses on top of the kit.
The title of day three of this build referenced $15,000 plus going into the car across the hardware alone. That figure gives a realistic framework for planning a 4N Motorsport single turbo conversion on an S55-powered BMW. It is not a budget modification. It is a serious build investment that produces serious results.
The Complete 4N Motorsport BMW F82 M4 Parts List
Core 4N Motorsport Kit Components: 4N Motorsport bottom mount single turbo kit, Borg Warner turbocharger, tubular twin scroll equal length manifold, wastegate actuator and replacement rod, oil feed and return lines, coolant lines
Fuel System: Motive Reflex port injection system, port injection fuel rail, extended intake manifold studs, port injection plate and gaskets, low pressure fuel pump, J-pipe with transferred O-ring, ethanol content sensor
Engine Maintenance Items: Upgraded ignition coils, upgraded fuel injectors, valve cover and valve cover gasket, spark plugs gapped to 0.022 inches
Exhaust: Single turbo downpipe compatible with 4N Motorsport kit
Tuning: Professional remote or in-person dyno tune, Wedge Performance calibration on this specific build
Why This Build Is Worth Watching Even If You Are Not Building One
The four-video series documenting this 4N Motorsport build is useful content beyond just the build itself. Every installation tip in this article came directly from the experience of doing the job on a real car in a real shop. The wastegate actuator rod alignment. The J-pipe O-ring swap. The port injection fuel line confirmation before reassembly. These are the details that separate a build that runs correctly from the first startup from one that requires troubleshooting after reassembly.
Whether the 4N Motorsport kit is something you are planning to install yourself, something you want a shop to do, or something you are researching because you want to understand what a single turbo conversion involves before making any decisions, the complete four-day build series at Tysautoworks Performance covers it at a level of detail that is not available anywhere else for this specific kit.
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