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BMW E30 M50 Swap


BMW E30 M50 Swap

First I would like to give a word of advise to anyone doing this swap.  If your main goal is making your E30 fast, do not do a 2.5L swap.  Trust me you will be disappointed.In my opinion the smallest engine you should put in your E30 is a 2.8L M52.  The simplest and probably most economical engine to swap is a 3.0L S50 engine out of a 95 M3 primarily because it already comes with most of the OBD I hardware you will need for the swap.  The only problem with 95 S50 motors is that they are becoming old and it is very hard to find one in good low mileage condition for a reasonable price.  You might want to consider an option of building a high compression 2.8L engine that will perform on par with a 3.0L and cost less.  One good way of building a low budget high performance 2.8L is purchasing a 2.5L M50 engine out of a 525I (so you can get your oil pan) and stroking it.  There are plenty of 2.8L core engines out there for as little as $200.  One trick of making it high compression is reusing the 2.5L pistons (only if in great condition with new rings) with 2.8L rods and 2.8L crank.  The combination will give you a compression ratio of around 11.25:1 according to my estimates.  With M3 cams (ether 3.0L or 3.2L) the engine dynos at around 240-250 crankshaft horsepower with stock injectors.  Upgrading injectors would probably make even more power because the engine leans out and stops making power after 6200 rpm.  One downside to this high compression is you have to use the best gas money can buy.  Sometimes in hot weather the engine will ping even on a 91 gas so if 92 or higher octane gas is not available in your state you probably shouldn’t consider this option.

Brake Booster:

Use an E21 320I brake booster.  Some people use 325IX brake boosters but 320I boosters are cheaper and allow you to use your stock master cylinder.  One big drawback to an E21 brake booster is a noticible reduction in power assistance.  To make the 320I brake booster work in your E30 you will need to cut the shaft off to the same length as your E30 booster, grind it down to the same thickness and thread it with a 10X1.5mm dye.  Be careful here, if you screw it up you will need to go out and get another booster, the shafts are non replaceable.  Don’t forget to grind off some of the fins on the back of the intake manifold to clear the brake booster.

E30 M50 Brake Booster

 Note how the fins are ground down to clear the brake booster.


There are a bunch of different transmissions you can use in this swap.  Some people keep their E30 Getrag 260s but it requires fabricating a custom transmission mount and your shifter will be offset to the right by about 15-degrees.  My favorite transmission to use is S5D320Z out of a 95M3, 96-00 328 E36 E46, 96-99 M3.  The reason I like them best is probably the fact that you can use a 135mm guibo on them and they are rated for 320hp, which should give you plenty of room if you are planning future modifications.  S5D320Z transmissions are not the lightest but they are the strongest.  You can use your stock 325 or 91 318I IS transmission mount with any E36 transmission.  Don’t forget to use E21 320I transmission mounts (they are stronger then e30 or E36 mounts) and weld two cups to the transmission mount to prevent the engine and tranny from moving around too much and hitting the radiator (see pic).  The shifter arm has to be out of an E36 328 or M3 along with the aluminum arm that connects to the top of the tranny.

E30 M50 Transmission Mount

Transmission Mount Reinforcement.

Drive shaft:

If you are using a ZF S5D320Z transmission you will have to use a drive shaft out of an E30 M3, 98 M3 (U-joint type only), 87-88 325E or 96-98 E36 328.  Use the E30 center support mounted backwards on E36 drive shafts.


The ultimate clutch is of course E36 M3 but some people on the budget use an E36 328 clutch (it is the same diameter as M3 clutch).Those who use a 328 clutch can also use a flywheel out of an E46 323I or a 2.8L Z3.It is virtually identical to a 328 flywheel but lighter.


Cut some of the insulation off the heater blower motor cover.  Some people strip it completely but I take a long knife, put it parallel to the firewall and remove some material.  Do not get rid of the rubber drain on the passenger side of the firewall that drains the water from the wiper motor compartment or you will end up with water in your spark plug holes every time you wash the car.  Bend the heater pipes towards the driver’s side of the car and down about an inch to clear the intake manifold.

E30 M50 Heater Pipes

Engine mounting:

The engine can be installed completely assembled with all accessories except the front harmonic balancer, A/C bracket or A/C compressor.  I prefer to install the engines completely stripped since it makes it easier to connect the heater hoses.

E30 M50 Engine Installation

For the aluminum mounts you have to use the E36 arms.  The rubber mounts are out of an E24 E28 (part number 11 81 1 132 793).  The mounts have to be mounted in the outside mounding holes of the sub frame.  It is a good idea to reinforce the sub frame if you are using a 3.2L motor.  Some times the engine mounting points rip out from a lot of torque.

BMW E30 M50 Engine Mount

Note the aluminum spacer under the engine mount.

Cooling System:

The radiator has to be out of an 88+ 325 E30.  Some people use E36 radiators but if you plan on using a mechanical fan E30 radiator will give you more clearance.  Speaking of clearance it is very important to reinforce the transmission mounts or the first time you slam on your brakes the fan will end up destroying your radiator.  The fan clutch has to be stock E30 with a 9-blade fan.  Do not use an 11-blade fan because it will give you less radiator to fan clearance.  The overflow tank has to be out of an 88+ E30 as well.  Don’t forget to upgrade the thermostat housing and the water pump to the metal kinds on your M50 motor.  The bottom radiator hose off the M50 motor will need to be cut down to fit in E30.  The top hose you can get from any auto part store.  Just look for a long radiator hose with a 90-degree bend.  The heater hoses connect the same way they were on your E30 (the long hose under the intake manifold goes to the top inlet and the short hose that connects to the cylinder head goes to the bottom inlet), do not eliminate the bypass valves (recall items).

BMW E30 M50 Radiator Clearance

Note how little clearance there is between the fan and the radiator, only about 7mm.

Lubrication System:

The oil pan has to be out of an M50 powered E34 525I.  You will also need to get the pickup tube with a gasket and the oil dipstick.  E36 dipstick can be modified to fit but it will not show you the oil level correctly.  Do not forget to safety wire the oil pump or at least locktight the sprocket nut.  Drill a hole through the oil pump shaft and the bolt, insert a stainless steel wire through the hole and tie it up, or you can weld the nut to the pump shaft.  M50 engines are known for the oil pump sprocket bots to come loose.  Oil coolers are also a good idea for the track.  Oil temps get to about 240+ degrees if you drive your car hard enough.

BMW E30 M50 Oil Pump


Just about every town has a shop that will fabricate customs A/C hoses.  When you get your engine from a junkyard try to get the A/C hoses with it.  Custom hose shops will be able to connect the E36 A/C hose connectors to your existing E30 hoses.  You can also get some fittings from your local hardware store and clamp the hoses together yourself.  Don’t forget to flash out your system to get rid of all R12 oil.  Use PAG oil only with your E36 compressor or it will not last you very long.


The best ratio for 3.0L or 3.2L cars is 3.25 and the best ratio for a 2.8L or a 2.5L is differentials can be found in E28 525e 535I E24 635.3.46s can be found in same cars but are more rare.  The output shafts and the rear cover have to be swapped to make the differentials work in E30.  You can also get a rear cover out of an M Coupe.The M Coupe covers lower the differential oil temperatures and look very cool behind your E30.


Exhaust is truly something that should be left to a professional unless you are an experienced welder.  You can use the stock E36 cats out of a 92-95 325 or M3 but the right side pipe will need to be modified to clear the control arm bushing mount.

BMW E30 M50 Swap Exhaust

As you can see the right side exhaust pipe is still very close to the control arm bushing bracket.In this case there is only about 5mm of clearance.

The O2 sensor mounting port interferes with the frame reinforcement behind the transmission mount.  You can cut a chunk out of the brace to make the O2 sensor fit and reinforce the brace by welding it to the transmission mount with a couple of pipes.

E30 M50 Transmission Brace 

 BMW E30 M50 O2 Sensor

96+ exhaust pipes are larger in diameter then 92-95 and pose some clearance issues.  96+ exhaust pipes are bigger in diameter on the outside but they are double walled so in reality they don’t flow more then 92-95.  OEM pipes are stainless steel and a very hard to weld unless you are equipped to weld stainless steel.  Stock cast iron headers from 92-95 can be used.  You will need to make some 5 mm spacers for the engine mounts to raise the engine so the pipes clear the sub frame.  It is also a good idea to remove the studs out of the headers and use the bolts to mount your exhaust, makes it way easier to get the pipes in there.  The left exhaust pipe will need to be flattened out to clear the sway bar.

BMW E30 M50 Downpipes

You can also use stainless steel headers from 96+ E36; they look way better then the rusty cast iron headers.  To use the 96+ headers buy two O2 sensor plugs from your BMW Dealer (originally install on a 98 323IS) and weld up the air injection ports.  The muffler is up to you but the pipes to it will have to be custom made.


When you get your engine try to get the power steering pump and hoses with it.  It is a good idea to replace your rack when you are swapping the engine.  The rack in an M50 powered car is almost impossible to replace without considerably lifting up an engine or dropping the sub frame, the oil pan sits very close to the steering rack.

BMW E30 M50 Steering Hoses


Nothing needs to be done to suspension unless you want to improve the handling of your E30.M50 engine is slightly heavier then M20 (around 60lbs heavier).  Although 60lbs doesn’t sound like much you will be able to feel it.  Thicker sway bars do wonders on M50 E30s.

Wiring and Electrical:

The best wiring harness to use is out of a manual 93-94 325I due to its simplicity, although it is not that hard to modify a wiring harness from an automatic car or a car with traction control and EWS.  The process is as simple as laying the harness out on a table with a diagram in front of you and eliminating anything that is not necessary.  If you ended up with a harness out of an automatic car simply cut all of the wires out of the engine harness that belong to the automatic transmission computer.  Automatic transmission computer is wired directly to the engine computer harness; the only wire that needs to be modified is a “brown/black wire pin 26 transmission ECU” need to be connected to any “red/white wire on the main relay”.  ECU has to be out of a 93-94 325I with the Bosch part number ending in 413.  You can use an ECU out of a 95 325I or a 95 M3 but you will need a special chip that eliminates EWS.  To make the E36 harness plug in to your E30 you will need to make an adapter.  To make an adapter you will need to get a wiring harness connector off the E36 (body side) and an engine harness connector off an E30 (engine side).  See the table below for pin assignments.  The coolant temp sensor for the ECU has to be out of an E36 and the coolant sensor for the temp gage has to be out of E30 (single pin sensor brown).  Alternator has to be out of any 6-cyl E36, I prefer to use 80AMP alternators but if you have a powerful stereo you might consider using a 140AMP alternator (it will suck up more engine power though).  Starter has to be out of any E36, Z3, E46 323 328, E34 E39 or E30 318is.  Don’t forget to the engine ground strap, with M50 engine it mounts on the passenger side of the car.

E30 Wiring harness connector (body side)

Color 91 318is

Color 325I IS

E36 Wiring Harness Connector (engine side)


Pin 1 (alternator charge)



Pin 25


Pin 4 (coolant tem)



Pin 12


Pin 5 (oil pressure)



Pin 23


Pin 6 (Diagnostic Connector)



Pin 22


Pin 7 (Ignition switch)



Pin 21


Pin 8 (fuel consumption)



Pin 24


Pin 9 (engine speed)



Pin 20


Pin 12 (check engine light)



Pin 8


Pin 13 (fuel pump)



Pin 13


Pin 14 (speed signal input)



Pin 14


Pin 15 (starter thin wire)



Pin 15


Pin 18 (starter thicker wire)



Pin 18







Oil Level Sensor





Pin 10





Pin 16





Pin 2










Note: Wiring colors can vary depending on model and year of your E30 and E36 wiring harness.





 On 325E the fuel consumption gage signal and the tach signal connectors are in the glove box.  Speed signal wire from pin 14 E36 connector has to be connected directly to the green plug on the back of your instrument cluster.  Thin (black/yellow pin 15 E36 connector) wire that goes to the starter can be left disconnected.  The starter will still work.