M5x Inlet

M52 2.8 (left) and M50 2.5 (right)

The M50 and M52 engines are essentially the same platform, with the M52 having a number of nifty technological features that give it an edge over the older M50.

But the intake system isn't one of them. BMW seem to have intentionally strangled the M52 by fitting a narrowed inlet manifold. This chokes the engine, preventing it from pumping out too much nasty pollution that the European Union is so afraid off, but at the same time holding back a fair amount of horsepower that could otherwise be put to good use. (It should be noted that, although fitting the M50 2.5 manifold will provide an increase in top end power due to better airflow, it will come at the expense of low/mid range torque. To obtain the best out of the conversion, a trip to a rolling road/ECU remap is recommended).

Fortunately for you, it's fairly simple to fit an M50 inlet manifold on to an M52 engine to harness that power, but you have to have a basic idea of how to go about it. You can't just slap on any old plastic pipework and expect it to work. So here's all you need to know about the M50/M52 inlet.

Identification

You can't just use any old M50 inlet for this upgrade; it needs to be from a 2.5 engine (the M50B25 or M50TUB25). 2.0 manifolds will offer no gain, and may even restrict your M52 further. However, that doesn't stop unscrupulous individuals trying to sell 2.0 manifolds as 2.5 ones, so you have to know how to spot the difference before you part with your hard-earned.

This picture shows a 2.0 manifold (above) and 2.5 manifold (below). To the casual observer, they could easily be mistaken.

To distinguish the difference between the two - notice the 'ribs' on the sides of the 2 middle inlet runners on both the B20 and B25 manifolds. The B25 manifold ribs are much thinner because the inlet runner is larger whereas the B20 one is larger because the inlet runners are smaller. More specifically, the diameter of the inlet port is larger on the 2.5 at 80mm, compared to the 2.0's 70-75mm. The final proof is the part number, which is cast onto the side of the manifold. For 2.0 manifolds the number will end with 2.0, but it's small lettering and would be missed if you didn't know exactly what you were looking at.

For further clarification - the B25 inlet manifold pictured here was taken from an E34 525i (not sure what year) and the B20 one was removed from a M50TU (VANOS) E36 320i. Please take into consideration that there are quite a few different types of M50 B25 and M50 B20 inlet manifolds with different sensor holes and such depending on which vehicle it came off. Other M50 B25 inlet manifolds have been found which do not have some of the holes visible in these pictures, and vice versa.

Installation

Here we have the M50 inlet manifold with M50 throttle body. What you are looking at is the underside of the manifold, showing the hole in the centre that the ICV pipe connects to. The plug sensor is for the air inlet temp sensor and the thin rubber pipe is what connects to the fuel pressure regulator.

This pic is a close up of the throttle body. Note the inlet and outlet at the bottom (it's upside down in this pic); these are the inlet and outlet for coolant for the throttle body heating which are not needed and can just be left open like in this pic. Note also the bit of bent rubber hose. This is on a connector which needs to be blanked off, so there's a bolt in the end and a jubilee around it to seal.

This is showing the MAF sensor and inlet elbow, which is from an E34 525i. It has two inlets on the bottom of it. One of them connects to the crank case breather (the long hose) the other one connects to the Idle Control Valve (pictured)

On a 328i there is a cylindrical shaped oil separator valve that plugs into the inlet bellows and is on the end of the hose that comes from the crank case breather. You can dump that and just replace it with a length of heater hose like I have done above. This is recommended if the car is mainly used on the track. However, if the car is mainly used on the road, fitting of this oil separator valve is recommended. This process will be shown further down in the article.

This is the connector which fits at the end of the swan neck shaped pipe that comes from the idle to control valve and goes into the port in the centre of the inlet manifold shown in the first pic. Mine had a snapped off retaining tab, so I got a new one as I thought this may be moving about a little and giving me an air leak/ occasional hunt at idle. I've fitted it and even still they are a pretty crap fit. The little nipple on the side needs blanking off.

This pic shows the inlet manifold getting ready to be fitted. The ICV and plumbing is connected.

Fitting it just involves dropping it on the studs. My gaskets on the inlet manifold were replaced when I fitted out the touring, worth replacing yours and checking ALL vacuum pipes to avoid crap running and future dramas.

Manifold now in place. Fuel rail and injectors pushed in, note the brass fittings on the top of the manifold next to the mounting tabs on the fuel rail. They don't line up. The throttle cable (E34 525i) has been fitted, throttle position sensor connected up. Also remember to connect up the 2 pin air temp sensor underneath (shown in first pic). Servo vacuum pipe connected up (clio servo)

This shot has been taken to show the pipes that connect to the underside of the inlet bellows. The long pipe on the left is connected to the crank case breather outlet on the cam cover at the top of the pic. The other pipe is what comes from the Idle Control Valve.

Injectors

You can use the M50 fuel rail that fits into your inlet manifold, but you still have to use the M52 pink injectors. If you want to keep your M52 fuel rail, you'll need to make up some tabs to secure it, since the M52 fuel rail doesn't line up to the mounting tabs on the M50 inlet. So the solution is to knock up some brackets. I just used some aluminium plate and drilled two holes.

This holds the fuel rail in place. And they look like this. You can obviously do a smarter job if you're that way inclined, but this lot is covered by the plastic cover that fits over the top.

Throttle Bodies

When you try to fit a M52 throttle body to a M50 manifold you end up with a ribbed rubber gasket gasket facing a ribbed rubber gasket. To get over this you just need to make up an aluminium or steel plate drilled to fit over the studs, with a throttle body sized hole in the middle, to give each gasket a flat metal surface to press against.

Fitting of Oil Separator Valve

Drill a hole into the intake manifold corresponding to the size in in the original. Fit the original rubber seal and press the oil separator valve in.

Refer to pics below showing the valve fitted to the M50 manifold:

If you have drilled the hole correctly, the valve should be a tight fit and not need a bracket to secure it from falling out. But you can make a bracket for piece of mind..

The pipework will be the same as in the original: the bottom hole in the separator to the drain in the dipstick tube and the upper to the rocker cover. You can make up a custom pipe to suit using the connectors from the OEM pipe and some oil resistant piping, like so..

Conclusion

Hopefully this shows how to have a go at this and that spending £350+ or whatever silly figure for the "Alpina527" kit is unnecessary. My car does not smoke or use oil as a result of losing the oil separator valve.

Full credit to E30BeemerLad and Leo_328i for the photos and technical description