The M50 > M52TU/M54 Intake Manifold Swap--Revisited
Updated: May 19
The M50 intake is legendary for its air flow capabilities which let engines rev freely past the factory manifold choke points - extending the powerband all the way to redline. For this reason, race teams have been retrofitting these manifolds for years onto all M5X series of engines, but we just made it easier! The factory manifold is bulky, heavy, and makes getting to the throttle body a huge pain. The air also has to make a bunch of tight corners to actually make it to the engine as well, not the best for flow! The M50 manifold is a simple design using long and wide runners and a shared plenum with the throttle body in the middle. This helps distribute air evenly between cylinders and allows the engine's air reverberations from the valves opening and closing to even out at high rpm and assist with flow into the engine.
Typical gains from this mod are 15-50hp depending on the setup (NA, Turbo, Supercharger, etc). Low rpm power loss while NA is around 5hp, but nobody tries racing between 2-3k rpm so that doesn't matter much.
On top of that, the M54 manifold is known to leak from a variety of places such as the intake hoses, DISA diaphragm (not designed for boost, functions via vacuum), the ICV rubber fitting and vacuum hoses on the back. It also takes up an exorbitant amount of room in the already cramped engine bay. By converting your build to a M50 manifold you free up a ton of room in your already cramped engine bay, fabricating intake tubing becomes much more simple, and overall reduces the chance for boost and vacuum leaks.
Here are some informative YouTube Install Videos:
Lets go through some details on installation:
Plugging Head Ports First, to install the M50 manifold you need to plug the ICV ports on the M52TU/M54 head. To do so is easy, and can be done with the head on the engine. Take the included black set screws and screw them into the ports. This is best done with an Allen socket on a ratchet so you can apply pressure down. No tapping is necessary, just a little elbow grease and thread sealant. They will self tap as they go in.
Here you can see the ICV holes are threaded after forcing the grub screw in, and then removing them to add sealant.
You want to tighten them down until they are flush with the head. If they get jammed, remove them ,clean the threads, and screw them back down. Apply thread sealant on the way in, or once the head is "tapped" remove the plugs and apply the sealant and then reinstall.
Port Matching Now, the decision to port match is a personal one. The gains made are not huge, but port matching is worth it if you are going for every last horsepower. Our included templates makes port matching easy with a dremel or air grinder. Just grind the the port out to the edge of the black plastic template. This template is the same shape as the manifold and acts as a marker. Don't grind past the edge of the template. Also, do not leave these templates on the head. They will cause a vacuum leak and they are just for use as a template, not as a gasket.
Porting template sitting on the untouched head, with ICV screw installed
This porting can be done on the car, just make sure the valves are closed on the port you are working in, and that you use a vacuum/ or air compressor to clean out the port after grinding. Rotate the engine when you move to the next port until the valves close and so forth. This is a similar procedure to how BMW N54 ports and valves are cleaned with a walnut blaster on the vehicle without getting any debris in the engine.
A port matched intake port
Fuel Rail Next is the fuel rail and you have a few options. You can either adapt the M52TU/M54 fuel rail using our adapter kit. This is easy, just cut off the original fuel rail bracket arms so the rail can clear the larger M50 runners and then bolt on our brackets. Or if your feeling flashy, you can use the optional billet fuel rail. This rail doesn't require any modification. Just bolt on and go.
SLG Fuel Rail Adapters
Billet Fuel Rail Factory injectors fit in the manifold and rail without problem. If you are using aftermarket injectors, such as EV14 injectors, use our injector spacer kit option (can been seen in picture below(silver piece). These go above the lower O-ring and stop the injector from falling too far down the injector seat. Depending on the aftermarket injector used, you may have to use a spacer cap. All these do is effectively make the injector taller or shorter(blue piece in picture below). They are cheaply available in a myriad of sizes on eBay. The injector port size you are looking for is 14mm.
Intake Hoses/ICV (Idle Air Control Valve) If your on a budget, you can use the factory M50 throttle body and ICV hoses as the ICV unit is the same between engines. I guess BMW figured if it wasn't broke, don't fix it! If you are boosted, we recommend using our silicone hose kit and billet ICV fitting. The billet ICV fitting replaces the factory fitting which kind of loosely snaps into the manifold and is sealed with a small O-ring. The billet ICV fitting is much stronger, has a wide O-ring, and wont fail and give you a massive boost leak under high pressures and temperatures.
Intake Air Temp Sensor The M50 intake uses a different intake air temp sensor than the M52TU/M54. Its scaling is different, so if you use the sensor that comes in the M50 manifold the air temperature the ECU reads will be off a bit.
Luckily we have a few options to get around this! If you are handy with tuning software you can change the scaling to suit and use the M50 sensor. This will come with our M50 tunes so you don't need to buy or thread a sensor.
Next, if you have a MS42 or MS43 vehicle (pre-facelift or Xi) you can thread the original plastic M52TU/M54 sensor with a tap to fit in the M50 sensor boss. We will have these sensors pre-threaded available on the store shortly to make it easy, or you can purchase from bimmerworld- http://www.bimmerworld.com/Modified-Air-Temperature-Sensor-for-M50-Plenum-Conversion_2.html
Finally, if you have a MS45 (Facelift) vehicle, no worries at all! Leave it in there to seal the hole, your MAF sensor has the air temp sensor integrated into it so you don't have to do anything extra.
Throttle Body So this can catch people up. The gold aluminum adapter plate we offer is for M54 models only. It is to adapt the electronic throttle body onto the manifold. This plate works for both the larger 3.0 throttle body and the smaller 2.5 throttle body. The throttle bodies go on at an angle, so if the bolt holes don't seem to line up at first, throw it on at an angle and you'll be set. The 3.0 and 2.5 engravings mark which set of holes you should use.
The M52TU throttle body actually has the same bolt pattern as the M50 manifold. Only problem is they both have O-rings, so just attaching them onto each other can create vacuum leaks. Best way around this is to use the spacer plate we will be offering soon. Its just a way to make both O-rings happy. The throttle body orientation is vertical when using this throttle body, so you'll have to get a little crafty with your throttle cable routing.
Intake VANOS Solenoid Connector
The runners are so wide on the intake runners on the M50 that the intake VANOS solenoid connector interferes with the manifold. Easy fix!. Just remove the plastic "elbow" casing from the connector by releasing the small clasps with a pick or tiny screwdriver.
Brake Booster Hose The original brake booster hose in the E46 goes to two locations, the bottom of the manifold and the intake hose. We can simplify this and run it directly to the manifold with the M50 manifold if you like.To do this remove the OEM Y-fitting and run a hose using the original brake booster barb fitting (which has a one-way valve in it) directly to the large manifold barb. Alternatively, you can run it like OEM, keep the Y-fitting, and go to the large manifold barb and then to the second hole on the silicone hose kit we offer.
CCV Removal/Catch Can One of the most underrated upsides of fitting the M50 manifold to your E46 is the excuse to get rid of the horrible CCV system. To do this, just cap the dipstick where the CCV oil drain originally went (and drained gross sludge back into your engine) and throw the rest of it in the trash.
Then, route a hose from the large valve cover vent barb on the front of the engine to a catch can. Although many like to bench race about the need of vacuum on the engine, venting to atmosphere is perfectly fine. If you really want to apply vacuum to the catch can system, you can either run a hose from the catch can to the second port on the silicone hose kit or to a exhaust venturi, which is available in our universal store section. Below is a picture of a simple catch can setup on a car with a M54 manifold. Check out our catch can kits as well if you want a badass setup!
Vacuum Hoses Vacuum hoses should reference manifold pressure, so just run them to any of the many vacuum ports. Or, just drill a hole and install a 1/8 NPT hose barb adapter into the manifold for some extra ports if needed.
The BMW ECU can account for a change in air flow by using its sensors such as the MAF (Mass Air Flow Sensor) or its primary upstream oxygen sensors. Other than a check engine light from deleting the DISA valve, the engine will run well using the factory tune with the M50 intake manifold. However, If you are looking to make the most of this upgrade, get your engine singing as well as it can, and delete those pesky check engine lights- a tune is for you. These are available here: https://www.seemslegitgarage.com/product-page/b-a-tuned-ecu