The following article is geared towards those whose BMW's have the 2.8 liter BMW M52 six cylinder engine. This engine is found in the 1996 328is, 1996 328is, 1996 328ic, 1997 328i, 1997 328is, 1997 328ic, 1998 328i, 1998 328is, 1998 328ic, early 1999 328is, 1999 328ic, 1996 M3, 1997 M3, 1998 M3, 1999 M3, all 2.5 and 2.8 liter Z3 coupe and convertible models, and all S52-powered M coupe and M roadster models The M50 manifold will also work well with a properly uncorked 2.5 liter M52 engine, which is found in the 1997-1998 323i and 323is.
Why Swap your M52 or S52 intake manifold out for a M50 325i manifold?
The OBD-II emissions-meeting M52 and S52 engines were introduced to the United States market for the 1996 model year. Evolved from the previous M50TU and S50 engines, these new engines had many changes, which included a more restrictive intake manifold designed to address the soft low end criticism the 2.5 liter M50TU engine received. While low end and mid range torque delivery was improved, the new stock manifold design is restrictive at higher rpms and chokes the breathing of the new larger engines. One popular modification for OBDII owners is to swap in the M50/S50 manifolds. With the bigger displacements of the 328 and M3, this can really help to wake up the car and allow it breathe at higher rpms. This also means you can stop dreaming about that expensive Schrick intake manifold, because an M50 one offers pretty much the same improvements. Ideally, you will also run software to maximize the gains and efficiency by optimizing the fuel air ratio. Dinan, Jim Conforti, Turner Motorsports, and Bavarian Autosports all sell this software, colloquially called the 'shark injector' as the Jim C software is known.
Instructions for removing your M52 or S52 Manifold and Installing the M50 one
First remove the stock manifold. Do this by removing the fuel rail cover (two bolts). Once it is off you can bleed the fuel pressure left in the rail by opening the valve at the front and use a small screw driver to depress the pin.
Next start removing the ASC Throttle body then the main throttle body. There's no reason to disconnect the linkage, just set it aside
With the throttle bodies removed, you can remove the two bolts holding the fuel rail down. Then pull the entire fuel rail and injectors back out of the way. So don't remove the injectors from the rail but you can if you need the extra clearance.
Next remove the nuts the attaching the manifold to the head. Also remove the two bolts (one in the front and one in the back) that attach the manifold to the support brackets. Now carefully remove the manifold. There will be three vacuum lines (two small ones and a larger one) you will have to disconnect from the manifold to remove it. Also on the bottom of the crank case vent (big round thing under the front of the manifold) disconnect the oil drain line. Disconnect the IAT sensor harness and the Idle speed controller harness. With all these fitting removed you should now be able to completely remove the manifold.
Now remove the Idle control valve and the crank case vent assemblies off the OBDII manifold. Remove the IAT as well. As you see there is no place to mount them on the OBDI manifold, this is where the fun begins.
On the OBDI manifold, there is one large fitting in the middle right behind where the throttle body mounts with a smaller fitting on the side. At the back there is a small vacuum fitting and a threaded hole in the front. You will use the middle and back fittings later. You need to plug the front threaded hole.
Take the Idle Controller and remove the rubber O ring off the end. You will notice that the metal pipe is about one 5/8 dia. do the same with the crank case vent. Now you will need some 5/8 hose. You will also need a 5/8' tee fitting and a couple of 90 deg elbows and hose clamps. Some remount the idle controller to the rear support bracket.
Zip tie the crank case vent in place or mount it to the front support bracket. Reconnect the oil drain! Use the 5/8 tubing and tee fitting to connect the tubing to crank vent and idle controller.
You still have three more vacuum lines. The line that runs to the fuel pressure regulator (hard plastic line that runs towards the back of the motor will connect to the single vacuum fitting on the back bottom of the OBDI manifold. As for the other two you will need a vacuum tee to connect them together and then to the fitting on the side of the large connector that goes to the manifold seen above. Now reconnect the plug to the Idle controller. The IAT sensor will be relocated into the rubber elbow that connect the throttle body to the HFM. We'll connect this later. set the connector aside or you'll lose it under the manifold.
Next set the OBDI manifold into place and connect the vacuum lines. You should only have two connections to make. the one big one in the middle which has the smaller line already connect to the side and the vacuum line for the fuel press regulator goes on the bottom back. The vacuum line for the brake booster is in the same place on both manifolds. Go ahead and bolt the manifold to the head. As for the support brackets, will a little help, they will line back up. You will need to pry/bend them about an inch or so.
Now for the fuel rail. A slight mod need to be done first. On top of the rail are two holder for the O2 connector plugs. The one on the back need to be removed. Use a dremel or a hack saw and remove it. When reinstalling the fuel rail the fuel lines on the back will hit the OBDI manifold so VERY CAREFULLY bend them out a little bit to clear it. Next you see the mounting hole don't line up. You'll have to make a simple little bracket to bolt the fuel rail down. See the pic below
Next up is the Throttle body. Since the OBDI and OBDII gaskets are used in a different manner you will need two gaskets. Take a razor blade to one of the gasket and cut it down the center so you now have two rings. Place one half of the gasket in the manifold and the other half in the throttle body. Take the other full gasket and place it between the throttle body and the intake and bolt the throttle body on. replace the AST throttle body next
Now lets mount the IAT sensor in the rubber elbow. Just drill a hole on the bottom and pop it in. keep the hole small enough so it seals good. reconnect the harness plug to it.
Reconnect anything else you may have disconnected and you should be ready to go.
As for the fuel rail cover the OBDII cover will fit but it sticks up a bit. The S50 and M50 covers do not seem to fit any better, either. The problem is the OBDII fuel rail is different.
Miscellaneous Parts You'll Need List:
4 – ¾” plastic elbows
1 – ¾” plastic T
1 – 3/16” plastic Y
1 – 3/8” to 3/16” plastic reducer
2 - L-Brackets
14 – ¾” hose clamps
1 – 11” Zip tie
3 – 7” Zip ties
3 – Small nuts and bolts
3 feet of ¾” hose
2 feet of 3/16” hose
Some sheet metal
95 M3 intake elbow
The result of this work? You should see up to 20 horsepower freed up on the top end, with a low end torque loss of 4-6 wheel horsepower. This is a mod that is well worth your time if you drive with your foot to the floor. Add in an M3 3.15 or 3.23 differential and you will be staggered by how strong your 2.8 liter car feels. M3 owners report lesser but similarly impressive gains! | 
