top of page

BMW M40B18 Engine (Design, Issues & Tuning)

Updated: Feb 2

✔ This article has been fact checked.

BMW created the M40B18, a SOHC straight-four petrol engine, between 1987 and 1994. It has a displacement of 1.8L producing between 111-114hp and 162-165nm depending on the version.

It has a bore of 84 mm and a stroke of 81 mm. M40 engines were used to replace the original M10-series engines, which were well-liked and successful in BMW cars at the time.

This engine was used in the following cars.

  • 1987-1994 E30 318i

  • 1988-1994 E34 518i

  • 1992-1993 E36 318i

Table of Contents:

m40b18 engine

BMW M40B18 Engine Design

The engine is conventional and basic. Cast iron makes up the cylinder block. The cylinder head contains a SOHC 8-valve aluminium cylinder head with hydraulic lifters. The duration and valve lift of the M40B18 camshaft are 244/244 degrees (single pattern) and 10.6/10.6 mm.

In contrast to M10 engines, M40 engines use a timing belt rather than a chain.

The engine has electronic fuel injection and ignition as well as an aluminium intake manifold. Fuel injection systems utilised in E30 vehicles are Bosch Motronic 1.3 and Bosch Motronic 1.7 are used in E36 variants.

The 18i variations are covered under the M40B18 application. Since BMW had already invested two years in creating a successor engine, the M43B18, manufacture of this engine was stopped in 1994.

Engine Specs

  • Manufacturer: Steyr Plant

  • Production years: 1987-1994

  • Cylinder block material: Cast Iron

  • Cylinder head material: Aluminium

  • Fuel type: Gasoline

  • Fuel system: Fuel injection

  • Configuration: Inline

  • Number of cylinders: 4

  • Valves per cylinder: 2

  • Valvetrain layout: SOHC

  • Bore: 84.0 mm

  • Stroke: 81.0 mm

  • Displacement: 1796 cc

  • Type of internal combustion engine: Four-stroke, naturally aspirated

  • Compression Ratio: 9:1

  • Power: 113 hp at 5,500 rpm

  • Torque: 120 lb-ft (160 Nm) at 4,250 rpm

  • Firing order: 1-3-4-2

  • Engine oil weight: 5W-30, 5W-40, 10W-40, 15W-50

  • Engine oil capacity: 4.0L

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

  • Applications: BMW 318i E30, BMW 318i E36, BMW 518i E34

Reliability & Issues

Below is a list of the various issues a M40B18 engine may encounter.

  • Timing belt: It quickly degrades and is a common reason why valves bend. Keep an eye on the timing belt's condition. 

  • Knocking & ticking: Any broken camshaft must be replaced to prevent future costly repairs and knocking and ticking noises. In the event that the camshaft is worn out, the engine won't be able to rev high.

  • Electrical components: Engines like the M40B18 have outdated electrical components. If your idle is unsteady or you're having acceleration issues, check the air flow and oxygen sensors.

  • Fuel injectors: Dirty injectors are a typical issue that lead to excessive fuel use and power loss. The injectors might be changed to fix this.

  • Overheating: All BMW engines, including the M40, are susceptible to overheating. In accordance with your car's maintenance plan, don't forget to clean the radiator and top off the coolant in the system.

  • Age & mileage: The M40B18 engine has a 180,000-mile life span. The engine is dependable in and of itself, but finding a car with that engine and low mileage may be challenging.

Tuning & Performance Upgrades

The majority of users typically resort to remapping when tuning, however there are several more ways to tune your M40B18.

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, modified 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.


The shape and flow characteristics of the air intake manifolds on the M40 can significantly affect atomization. While few manufacturers offer adequately flowing air intake manifolds, the majority require motorsport modifications.

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


Fast road cams are one of the most crucial mechanical modifications, but they need to be installed by a skilled technician, and they're not always simple to find.

In most cases, these changes won't increase power on their own, but by removing the restriction, they could help enhance power following other mods.

Forced Induction

The most effective approach to increase air supply, allowing you to burn more fuel and produce more power, is via forced induction. Even though it is one of the priciest upgrades, it provides the most gains.


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

Power can be increased by enlarging the valves, adding port matching, and head flowing. As an added benefit, you'll be able to get a bigger boost from other tuning modifications.

ECU Mapping

You should use ECU mapping to maximise the performance of all the installed components in your M40B18.

Because the factory ECU is locked, flashing may not an option, thus an aftermarket ECU is the best option. Many of them will outperform original ECUs, but make sure it has knock protection and is fitted properly.

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


Below are images of the BMW M40B18 engine.



More Questions? Ask the Community

Our Promise

TuneAutos is a car, vehicle, and automotive information publishing company working to make honest, accurate, and unbiased information easy to find. Our goal is to provide the highest-quality automotive information possible.

All of our articles are subjected to the most rigorous editorial standards to ensure the best possible possible quality. See our process here.

bottom of page