Engine Swap - M5x

The standard when it comes to non-E30 swap. Whether its the simply grunty 2.5-litre M50 or the beefier 2.8 M52. all aspects are covered of fitting the next generation of six-pot rightness to your car.

On paper, there doesn't seem to be a huge difference in power between this generation of engine and its predecessor, the M20. But a basic horse-to-horse comparison is to miss the point of this engine swap. By utilising a more modern engine management system, the M5x generation of engines provide superior throttle response, better fuel economy and most importantly, great lashings of torque lower down the rev range.

They're also a relatively simple swap too. You won't be able to unbolt everything from a donor vehicle and transfer it directly into your E30, but the solutions are there to get the M5x installed in double-quick time, using either your won fabrication skills or some off-the-shelf aftermarket components.

It's not a cheap swap, but pound for pound it's the cheapest upgrade for those with an M20 looking for better performance, especially compared to building a stroker engine.

With that in mind, let's get started.

Overview

The M5x can be fitted to any E30, no matter what engine it started out with. However, for the sake of costs it does help to use either a Touring, a Cabriolet or a car that started life as a 325i, as these cars will already be fitted with the Suspension and Brakes necessary for the job. The 325i can also reuse its entire drivetrain from the flywheel to the differential, which is a benefit in terms of cost. However, even a humble 316 can be transformed into the ultimate sleeper car with the right bolt-on components.

M5x engines fit easily under the long bonnet of the E30. However, you will have to find custom solutions for the exhaust and loom. If you don't trust your own skills at welding and soldering, we'll point you in the direction of someone who can do if for you... but be prepared to stump up the monies for it.

As for the drivetrain, there are a number of options to mate your new lump to the back wheels depending on whether economy or performance is what you have in mind. We'll talk you through that in due course.

Parts List

The parts list depends on which engine your car has already; the venerable M10, the stalwart M40 or simply a smaller M20 engine.

For all swaps, you will need:

• Full engine with all ancillaries (injectors, MAF, inlet, coil packs, alternator)
• M5x sump from an E34 (the E36 sump will not fit)
• Complete engine loom
• ECU
• Exhaust
• M20 Cooling system of radiator inc. brackets, hoses and expansion tank
• M20 Coding plug for the Instrument cluster
• New rubber engine and gearbox mounts
• New rubber prop shaft guibo
• A mate on standby. An extra pair of hands can save your life.

The following M20 components can be used if available

• Exhaust system from manifold
• Flywheel and matching starter motor
• Gearbox
• Propshaft
• Differential

Service Parts

We also recommend you buy these parts as part of a general Service while the engine and gearbox are removed:

• Sump Gasket
• Oil, Fuel and Air filters
• Spark plugs
• Engine and Gearbox Oil
• Gear selector seal

Engine

Given the choice between an M50 and M52 lump, there's not much in it, as long as you go for the biggest available capacity. Anything less simply isn't worth the expense of the conversion. We therefore recommend you source either the iron-cast reliable M50B25, or the aluminium revvy M52B28. The former is normally found on the E34, while the latter is exclusive to the E36.

Flywheel

Standard and Lightened M20 flywheels

A variety of flywheels can be used, but this entirely depends on which gearbox you are planning to use. The main choices available are the Dual-mass flywheel that comes fitted with the M5x engines, the M20 flywheel which will need some material removing from its back, or the M42 flywheel.

Despite the work involved, most experienced swappers recommend the use of the M20 flywheel. The existing dual-mass wheel is not only extremely heavy but also problematic, and ties you to a gearbox with worse-performing ratios than its M20 counterpart, which can be used with any gearbox (including the M42).

Starter Motor

Despite being mounted to the gearbox, the starter motor is intrinsically paired with the Flywheel due to the differences in teeth pitch around the edge of the wheel. This means that an M20 starter must be used with the M20 flywheel, even if an M50 gearbox has been fitted.

The wiring for the starter motor is easily changed over, with the thick and thin red wires simply bolting up to their relevant posts no matter which starter motor you choose to use.

Mounts

Because of the differences in height of the M50 and M52 engines compared to E30 engines, there is a choice of engine mounts available.

Engines taken from the E34 have their engine mounts bolted to the front of the engine block. To fit these blocks in an E30 you need to bolt E36 alloy arms to previously unused holes near the middle of the block.

From there, it is recommended to use the rubber engine mounts from the E28 M5.

Throttle Cable

If converting to M50, then a standard E34 525 throttle cable should fit the E30 perfectly. This cable is part number 35411160611, and is available in two lengths; 635mm and 1170mm. It is the longer cable you want.

Drivetrain

Once you've fitted your engine, you'll want that power to be hitting the back wheels as efficiently as possible. With that in mind, you'll need to select the best combination for you from these three components; the Flywheel, the Gearbox and the propshaft.

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 the appropriate propshaft to mate up to the differential.

Two types of gearboxes were fitted to the E36. 328's were given a bigger unit (ZF S5D), while 325's and 323's got the smaller (and lighter) Getrag S5D. Both are fine for any M50 engine, but still necessitate a change away from the E30 propshaft.

The best gearbox to use is from an H plate 520i or 525i 24v. These early 24v cars used a Getrag 260 overdrive gearbox which is identical to an E30 325i and E34 525i unit, but the bellhousing bolt pattern is altered to make the engine sit over at more of an angle. This means you can use the existing 325i prop and not have to fit a different final drive

Clutch

The clutch has to match the gearbox you are using. No matter whether it's M5x, M20 or M42, the preferred brand of clutch is Sachs.

Propshaft

Depending on which gearbox you use, you will be forced to use a certain propshaft to make use of your new engine.

If you have fitted the M42 or M20 gearbox, then a standard E30 propshaft can be used.

If you have fitted a more modern M50 or M52 gearbox, then you have one of two choices. Try to buy a used E30 M3 propshaft, or make your own using E36 components. By using the front and rear halves of an E36 325 prop with an E30 centre bearing, you should be able to mate up your new gearbox to your rear diff with the appropriate propshaft length.

Combinations

Engine	Flywheel	Clutch	Gearbox	Propshaft	Modifications
M52B28	M20 325i	M20 325i	M20 325i	M20 325i	Modified E30 325 gearbox crossmember using E30/E36 gearbox mounting rubbers E30 325 gear shift rods which need to be twisted slightly
M52B28	M20 325i	M20 325i	M42 318iS	M20 325i	E30 318iS gearbox crossmember using E30/E36 gearbox mounting rubbers E30 320 gear shift rods If using the M42 box a new M20 spigot bearing is needed (12mm hole)
M52B28	M20 325i	M20 325i	E36 328i	E36 328i	Propshaft should be fitted with an E30 centre bearing fitted to the rear section Note the E36 box is a 1:1 final drive so a low ratio diff will be required (e.g. 2.93:1, 3.25:1)
M52B28			M40	E30 318/320	The props mentioned have a longer front section

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
DanThe	Full manifold and front pipes	POI	Contact here
Fritz' Bits	Full 6 branch manifold and exhaust system 2x2.5" system with a X-over pipe Lifetime warranty	1200 inc. VAT	http://www.fritzsbits.co.uk/exhausts.htm

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

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.

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.

ECU

M50 engines come with a red label 413 ECU or a silver label 413 ECU. The silver labeled ECU uses EWS

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.

Temp Sensor

E36 (left) and E30 temp sensors fitted to an M52

If you are running the E30 cluster, make sure you put in an E30 temp sender, as the E36 one will not operate the gauge properly. It is difficult to get to when the engine is in the car. Don't remove the existing one, as it also sends to the ecu; you will need to add the E30 one. If you are lucky there will be a blanked off spot to mount it in.

Removal

First off, you need to get your engine bay empty. Get a load of cardboard boxes, packing labels, plastic bags, zip ties and marker pens, and slowly dismantle everything in your cars engine bay. Start by disconnecting the battery and removing it from the car. Then drain the coolant system and dispose of the fluid responsibly. You can now start unbolting everything, but make sure you bag it and tag it as you go along, so you can refit anything later. Here's a handy checklist - cross them off as you disconnect them:

• exhaust
• exhaust heat shield (under car)
• propshaft
• gear shifter linkage
• clutch slave
• rear light switch cable
• throttle cable
• engine earth strap on the engine mount
• coolant hoses to the internal heater matrix
• Power steering hoses, if fitted
• coil
• ECU

You'll also want to whip out the radiator and headlights so that they don't get damaged, and store them somewhere safe.

Now you need to get your engine out. The quickest way is out the top with the engine and gearbox as one unit. To do this, remove the bonnet and store it. Crack and loosen the nuts holding the engine mounts, and remove the nuts holding the mounts to their rubber bushes. Loosen the gearbox subframe nuts too.

At this point some people find it useful to jack up the rear of the car to ease the angle of the dangle. Raise it onto ramps or blocks, just make sure it's secure. Now use a jack to support the back end of the gearbox as you remove the gearbox subframe. You can now introduce your engine crane, complete with balancer if you can; it makes the job a lot easier. Hook the crane up to the engine, and slowly lift the engine up and out of the way. Dispose of it as necessary.

Preparation

If you really need to, you can lift the new engine straight out of the donor vehicle and into the recipient. However, if you have the time we strongly recommend you perform the following procedures on the engine prior to fitting:

1. Replace the sump gasket. These are a weak point on M20 engines and are a real pain to swap in situ.
2. Remove the injectors and send them off for professional cleaning. This will give you significantly improved performance and economy. We recommend Injectortune.
3. Remove the exhaust manifold, replace the studs, then refit. Consider having the manifold skimmed for evenness. Be prepared to extract broken studs with a welded-on nut if necessary.
4. Change the cam belt. Some people forget that M20 engines have a belt rather than a chain, and only learn when the belt breaks, by which time the engine is toast.
5. Replace the clutch. The donor clutch may be well over 100k miles by now, and due for a replacement.
6. Replace the alternator belt. Might as well do it now.
7. Change the gearbox shifter seal. This little bugger is the cause of 99% of gearbox leaks. It takes 5 minutes and 2 pounds to do if the gearbox is off the car. It takes 5 hours if the gearbox has been fitted.
8. Fit a new distributor cap and rotor. You may have no idea how old the current one is.

Fitting

With your engine bay empty, take the time to clean and degrease everything, and deal with any Rust in the area.

Now fit your rubber engine mounts to the subframe. These are your targets for getting the engine in.

You'll want to drop the engine straight in with the gearbox attached and the engine mounts on. The mounting points for the M20 engine are the large visible ring at the front, above the distributor, and a smaller hole at the back of the block, just above the gearbox bell-housing, like so:

Once your engine's hooked up, it really helps to have the back of the car raised substantially because the engine and gearbox combined are very long and need a particular angle of attack to go in. Take your time and go slow. Your aim is to get everything over the front slam panel, then the gearbox output shaft pointing downwards enough to slide into the transmission tunnel. You'll need it to go down while still having the height to get the M20 sump over the slam panel. It helps to have a spare trolley jack to carry the gearbox as it bottoms out; this will help you pull the box into the car as the engine drops down.

Drop the engine onto its mounts and hand-fit the securing nuts. Use the jack on the gearbox to lift it up while you slide on the prop shaft with the new rubber guibo, then bolt on the gearbox subframe with new rubber mounts. While you're under the car, hook up the gear shifter mechanism and plug in the reversing light switch. When you're sure it's secure, remove the jack and engine hoist. If you are planning on changing the differential, now is the time to do so.

Space is now at an advantage, so work your way from the bottom to the top. Attach your steering pump and A/C compressor if required.

Start threading through the wiring loom since some wiring needs to go round one side of the engine to the front. Pay attention to how the alternator and starter are wired if you had them disconnected - check here for the starter wiring connections if you're not sure. Bolt the coil to the inner wing. Feed the ECU plug through the bulkhead, and mount the ECU. Join together the two halves of the C101, but don't connect up the battery terminals yet.

WARNING: It is essential that you check Pin 20 of the C101 plug for a brown wire. On early vehicles, Pin 20 is a brown earth wire, while for some later vehicles Pin 20 is a live, unfused red/yellow wire for the ABS system. If you are changing your engine, CHECK PIN 20 ON BOTH SIDES OF THE C101 PLUG before connecting the battery.

If you have a brown wire connected, cut it away from the pin, and make sure the free end can't come into contact with anything. If it is red/yellow, then leave it alone. Of course, if the body side of your C101 has a red/yellow wire on pin 20, and your new engine loom has nothing connected to this pin, you need to add a wire, capable of carrying about 15A, from either of the terminals marked '87' on the DME relay socket to pin 20 of the the C101 plug, otherwise your ABS braking system won't work.

You can then drop your radiator and hoses in to see if any adjustments need to be made. If it fits fine, leave it in. Fit the plastic shroud that goes around the fan.

Now you need to sort out your brackets. There'll be lots of bolting, unbolting, measuring and marking if you're fitting your Air Filter bracket, and potentially the same depending on which Expansion Tank solution you've gone for with your cooling system. The ECU relays just need to be held secure, and therefore don't have to be millimetre precise. However you attach your brackets, make sure they're painted, and any holes treated with a zinc-rich primer to deter rust.

You can now finish off the intake side of the engine. Connect the rubber intake boot, AFM and air filter. Fit the brake booster hoses to the intake, and make sure you have plugged in the following parts to the loom:

• AFM
• Oil level switch
• Idle Control Valve
• Throttle Position Switch
• Crank Position Sender
• Oil Pressure switch
• Engine earth/body strap - THIS IS ESSENTIAL. Do not crank the engine before fitting this.

Connect the fuel hoses the right way round, but remove the fuel pump fuse from the fuse box for the moment.

Then connect the battery and secure it.

If the engine is of unknown age, remove each spark plug and put a few drops of engine oil down the bores.

If you're ready, top the coolant system up with fresh coolant (50/50 water and anti-freeze). Set the cabin heaters to full and the fan blower to maximum, and crank the engine a few times to raise the oil pressure. Now put in the fuel pump fuse and crank the engine a few more times to raise the fuel pressure.

When everything's plugged in right, you should get the magnificent roar of a straight-six engine running without its exhaust. It is a Zone tradition to start a new engine without its exhaust, as a sign of success. Don't do it for longer than a few seconds, but enjoy the moment.

You can now connect up the exhaust side of things, including a catalyzer if you have one. Plug in the oxygen sensor if needed.

You're now free to finish off the installation by re-fitting the bonnet. Be aware that your new engine will need bleeding, to remove air trapped in the coolant system, so don't be too abusive for the first few miles of the drive. It can also help to let the car idle for the first ten minutes before taking it for a thrashing session, in order for the ECU to learn its new settings.

Upgrades

Since you've got the engine out, it's worth taking the time to perform these upgrades:

• Z3 Short Shifter
• Replace your front suspension - not necessary for 323i, Touring or Cabriolet models
• Upgrade the front brakes - not necessary for Touring or Cabriolet models