The BMW M4 powered by the BMW S55 is already a monster from the factory.
With 425–444 horsepower stock, the S55 is one of BMW’s most capable modern performance engines.
But what happens when you remove the factory twin turbos… and convert it to a single turbo setup?
That’s where the 4N Motorsport single turbo kit comes in.
Let’s break down what this conversion does, why people go single turbo, and how much power the S55 can actually handle.
Why Convert the S55 to a Single Turbo?
The factory S55 uses two small twin-scroll turbos. They spool quickly and make great midrange torque.
However, they have limitations:
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Limited top-end power
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Heat buildup at higher boost levels
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Efficiency limits past 600–650whp
A single turbo setup solves that by:
✔ Increasing airflow
✔ Allowing higher horsepower potential
✔ Improving top-end power
✔ Creating a more aggressive powerband
For serious power goals, single turbo is the next step.
What Comes in the 4N Motorsport Single Turbo Kit?
The 4N Motorsport S55 single turbo kit typically includes:
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Top mount turbo manifold
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Single turbocharger
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External wastegate
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Downpipe
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Oil and coolant lines
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Charge piping components
This setup eliminates the factory twins and replaces them with one larger turbo capable of significantly more airflow.
How Much Power Can a Single Turbo S55 Make?
Here’s where things get serious.
On stock internals, the S55 has proven to handle:
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600–650whp comfortably
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700+ whp with proper fueling
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Built motor setups can push far beyond that
With upgraded fueling (port injection, upgraded low pressure fuel pump, etc.), the S55 becomes a serious high-horsepower platform.
Your bottom-mount or top-mount single turbo build changes the personality of the car completely.
Twin Turbo vs Single Turbo S55
Factory Twins:
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Faster spool
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Smooth daily drivability
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Limited peak power
Single Turbo:
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Bigger top-end pull
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Louder turbo sound
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Higher horsepower ceiling
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More aggressive power delivery
The car feels completely different once converted.
Supporting Mods Required
A proper S55 single turbo build usually requires:
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Upgraded fueling system
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Port injection
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Low pressure fuel pump upgrade
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Custom tuning
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Strong clutch (DCT cars may need upgrades at higher torque levels)
Tuning platforms like MHD Flasher are commonly used for dialing in single turbo setups.
Without proper tuning and fueling, you’re risking engine damage.
Is a Single Turbo S55 Reliable?
Reliability depends on:
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Quality of install
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Quality of tune
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Fuel system support
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Maintenance intervals
The S55 has a strong closed-deck block and forged internals from factory, which makes it capable of handling serious power when set up correctly.
But this is not a “bolt it on and forget it” modification.
Is It Worth Going Single Turbo on an M4?
Go single turbo if:
✔ You want 650+ wheel horsepower
✔ You want a unique setup
✔ You’re building a serious street or roll racing car
✔ You want insane top-end pull
Stay twin turbo if:
✘ You want OEM-like drivability
✘ You’re keeping power under 600whp
✘ You prefer faster low-RPM spool