BMW M44 Engine: What's New?

The BMW M44 engine, specifically the M44B19, marked a significant evolution from its predecessor, the M42B18. Introduced in 1996 and produced until 2001, this 1.9-litre straight-four powerplant found its home in popular models like the BMW 318is/ti E36 and the BMW Z3. While sharing a common lineage with the M42, the M44 brought several crucial enhancements aimed at improving performance, efficiency, and reliability. Understanding these changes is vital for any enthusiast looking to maintain, repair, or even tune these classic BMWs.

BMW M44 Engine Specifications Overview

To fully appreciate the advancements, let's first look at the core specifications of the M44B19:

Key Changes from the M42B18

The M44B19 wasn't a complete redesign but rather a refinement of the existing M42 architecture. The primary objectives were to increase displacement and improve the engine's breathing and efficiency. Here's a breakdown of the most significant modifications:

1. Increased Displacement

The most apparent change was the increase in displacement from 1.8 litres to 1.9 litres. This was achieved through a combination of a slightly longer stroke and a larger bore:

• Stroke: Increased from 81 mm (M42) to 83.5 mm.
• Bore: Increased from 84 mm (M42) to 85 mm.

These alterations required new pistons and a revised crankshaft. The connecting rods were also modified, becoming lighter and longer (140 mm) to optimise the stroke-to-rod ratio, contributing to smoother operation and improved engine dynamics.

2. Cylinder Head and Valvetrain Enhancements

The cylinder head received its share of updates. While the overall DOHC 4-valve per cylinder configuration remained, there were subtle but important changes:

• Valve Sizes: The intake valve diameter remained the same at 33 mm, but the exhaust valves saw a slight increase in diameter to 30.5 mm. This improved exhaust gas flow.
• Hydraulic Lifters: Like the M42, the M44 continued to utilise hydraulic lifters, ensuring quieter operation and eliminating the need for regular valve clearance adjustments.

3. Intake System Overhaul

A notable upgrade was the implementation of a new intake system. This included:

• Variable Length Intake Manifold (DISA): The M44 incorporated the Double Independent Swirl Actuator (DISA) system. This variable intake manifold adjusts the length of the intake runners based on engine speed and load, optimising torque across the rev range. At lower RPMs, a shorter path is used for better low-end torque, while at higher RPMs, a longer path is employed for improved high-end power.
• Bosch DME M5.2: The engine management system was updated to the Bosch Motronic 5.2 Digital Motor Electronics (DME). This more advanced ECU could better control the DISA system and manage fuel injection and ignition timing more precisely, leading to improved efficiency and performance.

4. Water Pump Improvement

A common issue with earlier BMW engines, including the M42, was water pump leaks. BMW addressed this in the M44 by upgrading the water pump design, which generally resulted in improved longevity and reduced instances of leaks.

BMW M44 Reliability, Problems, and Repair

The M44 engine is generally considered a reliable unit, benefiting from BMW's robust engineering. However, like any engine, it is not immune to issues, and many of its potential problems are shared with its predecessor, the M42. The core mechanical components, such as the timing chain guides and oil scraper rings, have proven to be quite durable.

Common M44 Malfunctions

Owners may encounter a few common issues:

• Overheating: While the water pump was improved, a failing thermostat, radiator, or fan clutch can still lead to overheating. Regular coolant flushes and inspections are crucial.
• Rough Idle/Misfires: Issues with the ignition system (spark plugs, coils, or plug wires), vacuum leaks, or a dirty Mass Air Flow (MAF) sensor can cause a rough idle.
• Oil Leaks: Valve cover gaskets and oil pan gaskets are common culprits for oil leaks over time due to age and material degradation.
• DISA Valve Failure: The DISA unit itself can fail. A common symptom is a rattling noise from the intake manifold at idle or a loss of low-end torque.
• Coolant Expansion Tank Cracks: The plastic expansion tank can become brittle with age and develop cracks, leading to coolant loss.

For a more detailed understanding of potential issues, referencing information on the M42 engine's common problems is often helpful, as many stem from similar design elements.

BMW M44 Engine Tuning Potential

The M44 engine offers a good platform for tuning, whether you're aiming for naturally aspirated gains or considering forced induction. The modifications made for the M44, such as the improved intake and slightly increased displacement, already provide a modest performance uplift over the M42.

Naturally Aspirated Tuning

For naturally aspirated tuning, common upgrades include:

• Performance Exhaust System: A less restrictive exhaust can improve exhaust gas flow.
• Cold Air Intake: While the stock intake is decent, a well-designed cold air intake can provide marginal gains.
• ECU Remapping: Optimising the fuel and ignition maps can unlock more power, especially when combined with other hardware modifications.
• Upgraded Camshafts: More aggressive camshaft profiles can increase valve lift and duration, boosting power at higher RPMs.

Forced Induction (Turbocharging/Supercharging)

The M44 can handle forced induction quite well, especially with careful implementation. For instance, an affordable supercharger solution designed for BMW M44 16-valve engines can potentially produce 240hp+ at the flywheel (210hp+ at the wheels) from a standard engine. When considering turbocharging or supercharging, it's crucial to ensure the engine's internal components (pistons, connecting rods) are up to the task or consider strengthening them for higher boost levels. A comprehensive engine rebuild kit, using the same high-quality components found in professional builds, can be instrumental in preparing the engine for the stresses of forced induction.

M44 vs. M42: A Comparative Look

The transition from the M42B18 to the M44B19 was an evolutionary step, focusing on refinement rather than revolution. The key differences lie in the increased displacement, the introduction of the DISA intake system, and the updated ECU. These changes resulted in a modest increase in power and torque, along with potentially improved mid-range flexibility thanks to the DISA system.

What is a BMW M44 Supercharger?

As mentioned, a BMW M44 supercharger refers to an aftermarket forced induction kit specifically designed to fit the M44 engine. These kits typically include a supercharger unit, intercooler, necessary plumbing, and ECU tuning to deliver significantly increased horsepower and torque. They are a popular way to achieve substantial power gains on these engines.

Engine Rebuilds: Full Rebuild vs. Kit

When it comes to rebuilding an M44 engine, whether due to age or performance enhancements, the choice between a full engine rebuild and using a kit is important. A full engine rebuild by a reputable specialist often involves extensive diagnostics, machining, and replacement of all worn components to factory or better specifications. On the other hand, engine rebuild kits, like those offered by specialists such as Metric Mechanic, contain the same high-quality components used in their professional builds. These kits provide everything needed for a comprehensive overhaul, allowing for either a DIY approach or to be used by a machine shop. While full rebuilds might involve additional machining steps, the core components are based on real-world experience and are designed for durability and performance.

Frequently Asked Questions

What is the main difference between the M44B19 and M42B18?

The main differences are the increased displacement of the M44B19 (1.9L vs 1.8L), the addition of the DISA variable intake manifold, and the updated Bosch DME M5.2 engine control unit.

Is the BMW M44 a reliable engine?

Yes, the M44 is generally considered a reliable engine with a robust build. However, like any engine, it can develop issues related to age, such as cooling system problems or gasket leaks. Regular maintenance is key.

What are common problems with the M44 engine?

Common issues can include overheating, rough idling, oil leaks (valve cover, oil pan), and potential failure of the DISA valve. Many of these are shared with the M42 engine.

Can I tune a BMW M44 engine?

Absolutely. The M44 responds well to both naturally aspirated tuning (exhaust, intake, ECU) and forced induction (supercharging, turbocharging), with significant power gains achievable.

In conclusion, the BMW M44B19 represents a well-executed enhancement of the M42 engine, offering improved performance and refinement. Understanding its specific changes and potential needs ensures its longevity and enjoyable driving experience for years to come.