BMW N42B20 Engine (Design, Issues & Tuning)

Updated: Nov 23

The BMW N42B20 is a DOHC four-cylinder petrol engine manufactured between 2001 and 2004, it replaced the BMW M43. Its 2L displacement yields 141 horsepower and 200 nm of torque.


N42 engines have a DOHC valvetrain, VANOS (variable valve timing), and an aluminium engine block compared to its M43 forerunner. It also had Valvetronic (variable valve lift) for the first time in a BMW engine.


The N42B20 engine was used in the following cars:

  • 2001-2004 E46 318i/318Ci/318ti


bmw n42b20 engine

Design

Instead of having a fully cast iron cylinder block, the engine features an aluminium cylinder block with cast iron sleeves. The engine is therefore substantially lighter than earlier BMW four-cylinder engines.


The cylinder block has been fitted with a brand-new crankshaft, pistons, and connecting rods with a 90 mm stroke. The balance shafts on the N42B20 engine are the same as those on the M43TU engine. Engineers had to make a few changes in order to fit them within the new cylinder block.


The new aluminium cylinder block is topped with a 16-valve DOHC aluminium cylinder head. This is a significant advancement over earlier models, which had 8-valve SOHC heads. Exhaust valves have a diameter of 29 mm, while intake valves are 32 mm in size.


The N42B20 camshaft has a duration of 250/258 degrees and a valve lift of 9.7/9.7 mm. The engine uses the variable valve lift technology known as Valvetronic. The engine has a timing chain added.


The variable valve timing technology is integrated into both camshafts (Double-Vanos). An intake manifold with a variable shape that is electrically regulated is also present. To define this technology, BMW came up with the acronym DISA.


At both high and low rpm, it is intended to deliver optimum torque and power characteristics. A Bosch DME ME9.2 fuel injection system is used.


Specs

  • Manufacturer: BMW Plant Hams Hall

  • Production years: 2001-2004

  • Cylinder block material: Aluminium

  • Cylinder head material: Aluminium

  • Fuel type: Gasoline

  • Fuel system: Fuel injection

  • Configuration: Inline

  • Number of cylinders: 4

  • Valves per cylinder: 4

  • Valvetrain layout: DOHC

  • Bore: 84.0 mm

  • Stroke: 90.0 mm

  • Displacement: 1995 cc

  • Type: Four-stroke, naturally aspirated

  • Compression Ratio: 10:1

  • Power: 143 hp (105 kW) at 6,000 rpm

  • Torque: 148 lb-ft (200 Nm) at 3,750 rpm

  • Firing order: 1-3-4-2

  • Engine oil weight: 5W-30, 5W-40

  • Engine oil capacity: 4.25 litres

  • Oil change interval: 6,000 miles (10,000 km) or 12 months

  • Applications: BMW E46 318i, 318Ci, 318ti


Problems and Reliability

  • Diesel sound: The timing system is not entirely reliable. A stretched timing chain or its tensioner may be the source of the noise. A timing chain has a lifespan of around 60,000 kilometres.

  • Ignition coils: When spark plugs are replaced, ignition coils are susceptible to damage.

  • Overheating: Maintain the radiator's condition in the cooling system. After only a brief time of overheating, the engine will start to consume oil. This is due to the vulnerability of valve stem seals to failure.


Furthermore, the N42B20 engine has strict standards for oil quality. Use the engine oil that the manufacturer recommends. Electronics and cutting-edge technology are abundant in the engine.


The longevity and reliability are comparable to those of the M40 and M43 series engines, though.


Tuning

Remapping is usually the go-to for most people when tuning, however there are a verity of paths you can go down in order to tune your N42B20.


  • Stage 1 improvements include fast road camshafts, sports exhaust manifolds, panel air filters, drilled and smoothed air boxes, intake headers, and remaps/piggyback ECUs.

  • Stage 2 upgrades include the induction kit, sports catalyst and performance exhaust, ported and polished heads, altered fuel pumps, and high flow fuel injectors.

  • Stage 3 modifications include adding or improving forced induction (turbo/supercharger), twin charging conversions, engine balancing and blueprinting, internal engine improvements (head flowing porting/bigger valves), competition cam, crank, and piston changes to adjust compression.


Intake

The shape and flow characteristics of the air intake manifolds on the N42B20 may significantly affect fuel atomization. Despite the fact that certain manufacturers offer rather well-flowing air intake manifolds, the majority require motorsport parts.


Power may be increased by using larger intake pipes, smoother pipework, a cold air feed, or ram air feed.


Camshafts

One of the most crucial mechanical enhancements is the installation of fast road cams, but this requires a skilled mechanic who is not always simple to locate.


It should be noted that in most cases, these alterations won't improve power on their own, but by removing the restriction, they could help raise power following other modifications.


Forced Induction

The best method for increasing airflow is forced induction, which enables you to burn more fuel and generate more power. Even though it is one of the priciest upgrades, it provides the most gains.


Headwork

The goal of porting and flowing the head is to increase airflow while minimising flow restrictions and turbulence.


Increasing the N42B20 valve size, adding some port matching, and head flowing will also increase power, and as an added bonus, you'll be able to get a greater boost from other tuning adjustments.


Mapping

You should use ECU mapping to help you utilise all of the installed components on your N42B20 to their greatest capacity.


When flashing is not an option due to the factory ECU's lock, an aftermarket ECU may be the better alternative. Many of them will outperform original ECUs, but make sure it includes knock protection and is fitted properly.


The final result will depend on the equipment you've added and the condition of your engine, but it will typically give you about 30% more power on turbocharged cars and 15% more power on naturally aspirated engines.


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