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 in 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 a 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 probably 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 will 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 a 325IX brake boosters but a 320I booster is cheaper and will 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 a 320I brake booster work in your E30 you will need to cut the shaft off to the same length as your original 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 not replaceable. Don’t forget to grind off some of the fins on the back of the intake manifold to clear the brake booster.
Note how the fins are ground down to clear the brake booster.
Transmission:
There are a bunch of different transmissions you can use. 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 and E46, 96-99 M3. The reason I like it best is probably because of the fact that you can use a 135mm guibo and they are rated for 320hp, which should give you plenty of room if you are planning on any future modifications. The S5D320Z transmission is definitely not the lightest but it is strong and reliable. You can use your stock 325 or 91 318I IS transmission mount with any E36 transmission. Don’t forget to use the E21 320I transmission mounts, they are stronger than e30 or E36 mounts. Weld two cups to the transmission mount to prevent the engine and transmission from moving around too much, this will prevent the fan from hitting the radiator during hard braking. 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 transmission.
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.
Clutch:
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 identical to a 328 flywheel but lighter.
Firewall:
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 of the foam. 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.
Engine mounting:
The engine can be installed completely assembled with all the accessories except for the front harmonic balancer, A/C bracket and A/C compressor. I prefer to install the engines completely stripped since it makes it easier to connect the heater hoses.
For the aluminum mounts you have to use 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. Sometimes the engine mounting points tear off the subrame from a lot of torque.
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 distroy 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 to the aluminum type. The lower radiator hose off the M50 motor will need to be cut down to fit E30. The upper 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 originally. 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).
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. BMW E36 dipstick can be modified to fit but it will not show you the correct oil level. Do not forget to safety wire the oil pump or at least loctite 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. Some people just weld the nut to the pump shaft. BMW M50 engines are known for the oil pump sprocket bolts coming loose. An oil cooler is also a good idea if you are going to track the car, oil temps get to about 240+ degrees if you drive your car hard enough.
A/C:
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 hoses to your existing E30 A/C hoses. Although it is not a good solution, you can also get some brass fittings from your local hardware store and clamp the hoses together yourself. Don’t forget to flush out your system to get rid of all of the R12 oil. Use PAG oil only with your E36 compressor or it will not last very long.
Differential:
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 3.46. A 3.25 differentials can be found in E28 525e and 535I or E24 635. A 3.46 can be found in the same cars but they are more rare. You will have to reuse your E30 differential output shafts with the 5 or 6 series differential. You can also get an M Coupe rear diff cover. The M Coupe cover will help to reduce the differential oil temperature and it look very cool.
Exhaust:
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 in order to clear the control arm bushing mount.
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.
96+ exhaust pipes are larger in diameter than 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 any more than 92-95. OEM pipes are stainless steel and are 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.
You can also use stainless steel headers from 96+ E36; they look way better than the rusty cast iron headers. To use the 96+ headers buy two O2 sensor plugs from your BMW Dealer (originally installed 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.
Steering:
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.
Suspension:
Nothing needs to be done to suspension unless you want to improve the handling of your E30. BMW M50 engine is slightly heavier than 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”. It needs 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 temp sensor for the temp gage has to be out of an E30 (single pin brow sensor). 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 want consider using a 140AMP alternator. Keep in mind that a more powerful alternator will use more engine power. Starter has to be out of any E36, Z3, E46 323 328, E34 E39 or E30 318is. Don’t forget to connect the engine ground strap, with M50 engine it mounts on the passenger side of the car.
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Color/Pin#
91 318is
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Color/Pin#
325I IS
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E36 Connector
(engine side)
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Pin 1 (alternator charge)
blue
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Pin 1 (alternator charge)
blue
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Pin 25 Blue
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Pin 4 (coolant tem)
red/wht
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Pin 4 (coolant tem)
brn/violet
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Pin 12 Grn/gray
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Pin 5 (oil pressure)
brn/grn
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Pin 5 (oil pressure)
brn/grn
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Pin 23 Grn
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Pin 6 (Diagnostic Connector)
grn/wht
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Pin 6 (Diagnostic Connector)
grn/wht
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Pin 22 Grn/wht
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Pin 7 (Ignition switch)
green
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Pin 7 (Ignition switch)
green
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Pin 21 Grn
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Pin 8 (fuel consumption)
white
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Pin 8 (fuel consumption)
wht/blk
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Pin 24 wht/blk
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Pin 9 (engine speed)
black
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Pin 9 (engine speed)
black
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Pin 20 Black
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Pin 12 (check engine light)
brown
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Pin 12 (check engine light)
gray
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Pin 8 Gray
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Pin 13 (fuel pump)
grn/violet
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Pin 13 (fuel pump)
grn/violet
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Pin 13 grn/violet
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Pin 14 (speed signal input)
blk/wht
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Pin 14 (speed signal input)
blk/wht
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Pin 14 black/wht
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Pin 15 (starter thin wire)
blk/grn
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Pin 15 (starter thin wire)
blk/grn
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Pin 15 blk/yellow
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Pin 18 (starter thicker wire)
blk/yellow
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Pin 18 (starter thicker wire)
blk/yellow
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Pin 18 blk/yellow
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Oil Level Sensor
Pin 10
Pin 16
Pin 2
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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.