M5x

The BMW M5x range of engines are a line of 6-cylinder engines, fitted to BMW models between 1991 and 2001. The range is comprised of two main units; the M50 and the M52. All M5x engines are fundamentally based on the M20 engine that powered the E30 320i, 323i and 325i, and are therefore very popular engine swaps.

Versions

M50

The M50 engine first saw action under the bonnet of the E34 ad E36 as the humble 2.0 variant before being enlarged to 2.5 in 1993. Being little more than an M20 engine with a 24V head, these engines are great upgrades for those who have tired of the M20 donk. Considering there is no difference when installing, there is little or no point fitting the weaker 2.0 version of the M50.

M50 engines weigh 138kg

Engine	Displacement	Power	Torque	Redline	Bore	Stroke	Year
M50B20	2.0 L (1990 cc/121 in³)	110 kW (150 hp) @ 6000	190 N·m (140 ft·lbf) @ 4700	6750	80mm	66mm	1991
M50B25	2.5 L (2494 cc/152 in³)	141 kW (192 hp) @ 6000	245 N·m (181 ft·lbf) @ 4700	6500	84mm	75mm	1991

M50TU

After letting the M50 prove itself, BMW released a Technical Update for the engine in 1993, announcing the new engine as the M50TU. These units featured an even more complex head design incorporating VANOS technology; a variable-valve timing system that modifies the position of the intake camshaft. This has no effect on the overall power of the engine, but does improve torque at lower revs.

Because of this increased complexity, VANOS engines are best avoided for first-time engine swappers.

Engine	Displacement	Power	Torque	Redline	Bore	Stroke	Year
M50TUB20	2.0 L (1990 cc/121 in³)	110 kW (150 hp) @ 5900	190 N·m (140 ft·lbf) @ 4700	6750	80mm	66mm	1993
M50TUB25	2.5 L (2494 cc/152 in³)	141 kW (192 hp) @ 5900	250 N·m (184 ft·lbf) @ 4200	6500	84mm	75mm	1993

M52

The M52 brought two new things to the BMW range of engines. Dual-VANOS, and Nikasil.

M52 engines weigh 118kg

Engine	Displacement	Power	Torque	Redline	Bore	Stroke	Year
M52B20	2.0 L (1990 cc/121 in³)	110 kW (148 hp) @ 5900	190 N·m (140 ft·lbf) @ 4700	6500	80mm	66mm	1994
M52B25	2.5 L (2494 cc/152 in³)	123 kW (170 hp) @ 5500	245 N·m (181 ft·lbf) @ 3950	6500	84mm	75mm	1995
M52B28	2.8 L (2793 cc/170 in³)	142 kW (193 hp) @ 5300	280 N·m (207 ft·lbf) @ 3950	6500	84mm	84mm	1995

Components

VANOS

Rocker Cover

Despite the three styles of Head, the rocker cover is interchangeable across all M40 engines. It is positioned on 8 studs and fixed with M10 nuts. It has one hole for the Oil Cap, and one port for the breather hose.

When removing and replacing the rocker cover, it is worth replacing the rocker cover gasket.

Intake

The main difference between the 325 and 328 inlet is the plastic manifold and the size of the ports in it. This manifold is 10mm greater (width) in port size over the standard 328. The 325 has 55x25mm port's and the 328 has 45x25mm port size.

Wiring

Loom

Main article: M5x Looms

The M5x series of engines differ substantially from their M20 predecessors in the labyrinth of wires that wind their way around the engine bay. Fortunately, BMW designed them to be detachable, and therefore the primary engine loom is a one-piece component terminating in a plug called the X20. This plug is the counterpart of the C101 plug on the M20 loom, although the pin layout differs substantially.

You will therefore need to adapt the M5x loom to mate up to the existing E30 wiring. You can either buy a ready-made loom (we recommend DanThe) or use our loom tables to make your own.

EWS

Main article: EWS

EWS is the immobiliser system fitted to BMW models with M50 and M52 engines from 1994 onwards. Its basic function was to check that the doors were unlocked correctly and that the correctly-coded ignition key is being used. If it fails to detect the right signal, it will disable the ignition circuit, the injectors and the starter motor, which is a right pain if you're trying to do an M50 or M52 engine swap.

If you are trying to chip-tune your M5x engine, you will need to disable the EWS to do so. Learn more about disabling the EWS.

Around the Engine

Exhaust

One of the key features of the M5x engine swap is the exhaust. The standard systems fitted to the donor vehicles are not compatible with the E30, and therefore other solutions must be found to ensure that the exhaust not only does its job properly, but also fits around the steering rack and under the car.

The two options are a custom-made exhaust system using your own manifold and tubing, or to buy a completed kit. There are a number of suppliers of M5x-to-E30 exhaust systems, which we have outlined below:

Off-the-shelf Solutions

Supplier	Offer	Price (£)	Contact
Fritz' Bits	Full 6 branch manifold and exhaust system 2x2.5" system with a X-over pipe Lifetime warranty	1200 inc. VAT

Custom Solutions

Manifold	Method	Result	Exhaust	Method
Standard cast E36 rear manifold cast E36 front manifold	On the front manifold, remove a section between where the three primaries meet the flange, and weld back together		E36 Front pipes 325i E30 system	By chopping up the front pipes of an E36 system and a 325 E30 system and welding the bits together, you can connect to the standard 325 E30 system just in front of the gearbox exhaust mount

Gearbox

By far the simplest gearbox to fit to your M5x conversion is that fitted to the 318is. This M42-specific gearbox will bolt straight up to the engine and remove the need for any Drivetrain modification such as different differentials. It is also capable of accepting the E36 clutch and flywheel if required, although it is recommended to fit the M20 flywheel.

To operate the gearbox, gear linkages from the M20 gearbox should be used, and it is recommended to fit the Z3 short shifter complete with bearing.

If you wish to use a more modern gearbox, such as that fitted to the M52, then it should be mounted using an M20 gearbox crossmember, and will need an M3 propshaft to mate up to the differential.

Brakes

While the 24v conversion doesn't deliver much more raw power, it does make the E30 a lot more sprightly when it comes to accelerating. It is therefore crucial to make sure your brakes are up to scratch.

Because of the bulk of these engines, there is little room for a brake servo of the size usually fitted to the E30. Therefore the servo fitted to a Renault Clio (2000 or later) can be used with very little modification.

If you are considering a dramatic overhaul of the braking system, learn more about brake upgrades.

Servicing

Main article: Basic M5x Servicing

Common Problems

Not Starting

If NOTHING happens when you turn the key, then you have an issue with the red wire that feeds the ignition switch from the fuse box.

If nothing engine-related happens when you turn the key, then the issue is with the plain green wires that drive the ignition. These wires are found behind the glovebox, where you will probably find a pair not connected to anything; these need to be joined together.

In the same area as these green wires, you should find two single plug and sockets, each joining a black/yellow wire to another wire (plain black, usually). Disconnect both of these and plug the two halves with black/yellow wires together.

This bypasses the auto inhibitor switch, and arranges the wiring just as it would be from the factory on a manual car. Follow the two left over wires to a relay, remove the relay base, the wires, and the other wires to the relay, which you will find a lead to the area under the front console where your gear lever will be. You need to find the reverse light loom and gear lever grommet from a manual E30, which will connect between the reverse light switch on the gearbox and the plug you have found.

Overheating

The aluminium blocks used in the M52 are a lot more sensitive to overheating than the cast-iron M50. For this reason, serious overheating has been known to completely kill an M52 engine beyond economical repair.

Common Upgrades

M20 Flywheel

m20 clutch w/lightened flywheel, m20 gear linkages + current z3 shortshifter/bearing

See also

• Engines
• M20