Turbocharger 49373-03012 55243431

The turbocharger bearing part numbers 49373-03012 (and its variants 49373-03010 / 03011) and the OEM reference 

55243431 is a forced induction unit frequently used in small displacement, twin-cylinder “TwinAir” engines manufactured by Fiat / Alfa Romeo / Lancia. 

In particular, it is compatible with the Alfa Romeo MiTo 0.9 L TwinAir model.

The MiTo with the 0.9 TwinAir engine is marketed in various power states (for example, 62 kW / ~84 hp, or 63 kW / ~86 hp), 

and this turbocharger is a direct fit in many of those configurations. Turbo Diesel London+3PHESSIO TURBO OFFICIAL ONLINE STORE+3Turbo Motori+3

Because the TwinAir engine is small (875 cc, two-cylinder), boosting via turbocharging is essential to deliver

 usable power and torque while maintaining fuel efficiency and emissions performance.

Technical Specifications & Features

Below is a breakdown of key technical and functional attributes of the 49373-03012 / 55243431 turbocharger:

These features ensure that the turbocharger meets the durability, performance, and emissions needs that designers expect in a small, high-stress turbocharged application.

Performance Role in the MiTo 0.9 TwinAir

Because the 0.9 TwinAir is a relatively underpowered engine in its base, the turbocharger plays a pivotal role in making the car usable in real‐world conditions.

 Here are some of the functions and performance benefits:

1. Boosting Torque at Low RPMs
   With only two cylinders, without a turbo the torque curve would be very narrow and low. The turbocharger allows the engine

2. to produce usable torque (mid-range) at lower rpm, improving drivability in urban and highway conditions.

3. Power Enhancement
   The turbo helps elevate power from what would otherwise be a weaker naturally aspirated performance.

4. By compressing intake air, it enables more fuel to be burned for a given displacement, increasing horsepower and torque.

5. Efficiency & Turbo Lag Trade-off
   The design of a small turbo like the 49373-03012 is a balance between responsiveness (minimizing lag) and providing sufficient boost without overshooting.

6. Because it's matched to the engine size, turbo lag is kept in check, and the boost levels stay within safe limits for the engine.

7. Emissions & Fuel Economy Management
   A correctly matched turbo allows the engine to run with better combustion efficiency, reducing specific fuel consumption (fuel per unit power) and helping

8. meet emissions targets while still delivering acceptable performance.

9. Durability Under Thermal Loads
   In such small engines, thermal management is critical. The turbocharger must endure high exhaust gas temperatures, so materials, clearances,

10. and lubrication design all matter. Proper lubrication and cooling (oil and sometimes water cooling) are essential for longevity of the turbo.

Installation, Compatibility & Considerations

When installing or replacing the 49373-03012 / 55243431 turbocharger, the following points must be observed:

• Direct Replacement Fit
  Many aftermarket sources advertise that this turbo is a direct replacement (“plug & play”) for the original unit on MiTo TwinAir engines, i.e. no major modifications needed.

• PHESSIO TURBO OFFICIAL ONLINE STORE+1

• Gasket / Seal Kit
  A complete gasket kit (intake, exhaust, oil, coolant passages) must be used to ensure pressure tightness and avoid leaks.

• Oil Supply & Drainage
  Because turbochargers spin at high speeds and require constant lubrication, ensuring clean oil feed, proper oil pressure, and unrestricted oil return is essential.

• Any clog or restriction in oil lines can lead to catastrophic turbo failure.

• Warm-Up & Cool-Down
  After installation, following appropriate warm-up (idling to build oil film) and cooldown (letting engine idle before shutdown) procedures helps prolong turbo life.

• Actuator / Wastegate Calibration
  The wastegate or electronic actuator must be calibrated correctly to regulate boost pressure. Incorrect calibration can lead to overboost or underboost, harming engine or turbo.

• ** ECU / Engine Management Remapping**
  In some aftermarket “hybrid” or upgraded turbo versions, it may be necessary to retune the engine

• control unit (ECU) to take advantage of the turbo’s capabilities or to adjust fueling/ignition timing safely. alfi-turbo.com

• Matching Components
  Components like the intercooler, intake plumbing, exhaust downpipe, and air filter should be in good condition and properly sized,

• so they do not choke the performance of the turbo.

Market & Remanufactured Options

Because turbochargers are wear items, there is a healthy market for both new and remanufactured 49373-03012 units.

• Remanufactured / Reconditioned Units
  Many respected turbo specialist shops offer remanufactured units — they disassemble the turbo, inspect, replace worn parts, rebalance,

• and test. For example, one European supplier lists remanufactured 49373-03012 turbos at ~€305 (including VAT) for the Fiat / Alfa TwinAir series. Turbo Motori+1

• Aftermarket / “Hybrid” Versions
  Some sellers market “hybrid” variants that use upgraded compressor or turbine wheels, larger flow designs or improved bearings for slight

• performance gains (within safe margins). alfi-turbo.com+1

• Core Return / Exchange Basis
  Many turbo suppliers require the old unit (core) to be returned (often within a timeframe) to qualify for full refund or discount. Turbo Diesel London+1

• Price Range & Availability
  Listings on eBay and other platforms show this turbo (rebuilt) for around US $320–330. eBay Also, specialist turbo shops

• in Europe advertise new turbo + gasket kits for MiTo / Fiat applications. Turbo Diesel London+1

Before purchasing, one should verify exact part numbers, matching turbine and compressor wheel sizes, and the compatibility with the engine’s boost levels and control systems.

Example Use & Fitment Case: MiTo 0.9 TwinAir 62 kW / 84 HP

In the case of the MiTo 0.9 TwinAir rated at 62 kW (~84 hp), the 49373-03012 / 55243431 turbo is often the original or direct-fit turbo used in that configuration. 

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Typical scenario:

• The driver replaces a worn or failing turbo with a new or remanufactured unit of these part numbers.

• After installation, the car regains original performance, throttle response, and midrange torque that may have been lost due to turbo wear.

• If a hybrid or upgraded turbo is used, modest extra performance can be achieved, but ECU calibration and supporting systems must be accounted for.

Strengths & Limitations

Strengths:

• Well matched to small displacement twin-cylinder engine, balancing boost and responsiveness.

• Aftermarket support and availability of remanufactured units make replacements feasible.

• Proven track record in MiTo / Fiat TwinAir applications.

• With proper build and balancing, has acceptable durability under normal use.

Limitations / Risks:

• Because it is a small turbo, it has a limited margin for upgrade; pushing too much boost can lead to failure.

• It is sensitive to oil quality and lubrication — poor maintenance can drastically shorten its life.

• Improper installation, calibration, or mismatched supporting components may lead to performance loss or damage.

• In hybrid upgrades, the risk of overboost, heat stress, or exceeding the stock engine’s tolerances is higher.

Summary

The turbocharger 49373-03012 (OEM 55243431) is a critical component of the 0.9 L TwinAir engine in the Alfa Romeo MiTo, especially in the 62 kW / ~84 hp configuration. 

As a well-engineered small turbo unit, it provides the necessary boost to make the diminutive twin-cylinder engine viable for everyday driving—improving torque, 

power, and overall drivability while maintaining efficiency.

For replacement or upgrade projects, careful attention must be paid to compatibility, installation practices (oil lines, gaskets, actuator calibration), and possibly tuning

, if higher performance variants are considered. With proper care and correct installation, a quality new or remanufactured 49373-03012 turbo can 

restore or even enhance performance in the MiTo TwinAir engine.