The M50 > M52TU/M54 Intake Manifold Swap--Revisited

Updated: Sep 20, 2021

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.