N54 Manifold Swap Tutorial
To minimize car downtime on this swap I recommend prepping the N54 manifold as your first step. So these are the steps to prep the manifold for install…
The N54 manifold will bolt right up to the N52 head but you will have intake leaks because the intake ports on N54 and N52 heads are situated at different heights.
Here is a picture of a N52 and a N54 manifold both with string laid center to center over the mounting holes. You can see the runners sit at different heights above the string.
So we have to adjust the mounting height of the manifold on the N52 head to get it aligned. This way you won’t get lean codes and your ECU will properly meter the incoming airflow. (In my car I also actually measured more power after correcting the mount, so it’s definitely worth doing!)
The solution I use is to make nylon shims to put inside the metal sleeves that come inside the manifold. First tap out the 7 sleeves using a long 1/4” socket and extension:
*Note the center sleeve is smaller ID and OD from the others. It is the only one which will fit in the center hole of the manifold and you will not make a shim for this sleeve.
Along with these 7 sleeves gather 5 of the nylon parts and pull the front manifold bolt out of your car to use as a test fit. You might have to unplug the oil pressure sensor wire from the sensor but that is the only disassembly you will need to do on the car for getting this single bolt out. (Just remember to put this back on your car if you will be doing the swap later lol)
I use an angle grinder to make a channel along the sleeve holding it with a Vice Grip. This is the most tedious step of the manifold swap and will probably take 45 mins to an hour to get them all done.
You are going to grind a channel straight down the entire side of the sleeve. Do this for all 7 sleeves making the channel wide enough for a manifold bolt to drop down into the sleeve through the channel you cut:
Now that the 7 sleeves are done you can start on the nylon shims. These I also use the angle grinder, just make a channel that almost touches the bottom of the ID on these (like the metal sleeves). The nylon cuts super easy so go light and be careful:
Notice how there is just a touch of the original ID hole showing untouched by the grinder. I try not to go any deeper than that original ID hole.
Now you can press the nylon shims into 5 of the larger sleeves (not the single smaller sleeve that goes in the center of the manifold.). These press in easy by hand, and try to center them in the metal sleeve:
Once again test fit dropping a bolt into the sleeve/shim assembly from above make sure you can drop a bolt in and out from above. If not use the grinder again on the assembled parts (just a light touch up) so the bolt sits level in the sleeve and drops in and out though the channel:
Once the bolt drops easy into all 5 sleeve shim assemblies you can install them back into your manifold with the channels you cut at the top. I put them in the outermost holes to align the manifold on the head when bolting it up, like this:
The last step of this shimming process is you now need to open the center hole with the smallest ID sleeve on the manifold upwards a bit. This is because it’s a smaller ID than the other 6 holes. I just lightly enlarge that hole in the plastic manifold upwards like 1/16” to allow the mounting bolt to sit at about the same height as it does in all the other holes. You can do this with a dremel and carbide cutter or small grinding bit, or even a drill bit and upwards pressure. We are only working with plastic after all. If you look closely you can see how I removed some material at the top of this single center hole in the manifold (again the one where the smallest sleeve fits):
The next step will be to make a place for the PCV Heater Elbow to attach to your manifold and make a mount for the elbow. Luckily BMW already made a place for the Elbow to attach they just didn’t finish it:
So for this part we need to just drill out the blank area and the 2 screw holes. It’s very important that you don’t damage the wall of the large center hole because the PCV Elbow has a gasket that seals on the outside wall of the hole. So don’t slip and screw up the wall surface of the hole only remove the bottom of it. I use a drill to make a few holes and then connect them with a dremel and a small grinder attachment or carbide cutter attachment:
Then I use a 9/64” drill to open the 2 spots BMW left for the screws. The threads that go into these holes are about 3/4” long so make sure not to make the holes deeper than the screws, and try not to get misaligned and poke out the sides when you drill. Now if by chance you do screw up and poke too deep or out the side then I would say you can use some RTV in the screw holes when you mount the PCV Elbow for the final time and you’ll likely not have an issue (the manifold doesn’t see a ton of vacuum pressure.)
This is the end result you are shooting for. A very small lip (maybe 1/16”) around the circumference of the hole and the 2 screw holes drilled and true:
At this point you have done about as much prep as possible without taking your N52 manifold off the car. You have about 3 hours of work left once you get the old manifold out of the car, so get that out and know your car will be down until it’s done.
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Once you have your original manifold out of the car there’s a couple steps left to prep the N54 for install.
First we have to transfer the PCV Hose attachment “elbow” with the heater element. This installs on the location you opened up in the previous step and this is how it sits on the oem manifold:
Notice the place the wire plugs in faces forward and the PCV hose enters from above (when the manifold is on the car the runners are at the top).
So now take that PCV elbow off your old manifold and do a test fit into your N54 and make sure it seats deeply and centered. If it doesn’t you might have to open up the large hole in the manifold a little more with your dremel.
If you were to bolt this elbow in right now with the holes you drilled in the manifold you would find the PCV hose doesn’t enter at the correct angle and the wire is not going to be oriented to plug in on the side facing the front. I strive to stick with the OEM arrangement because I’m not sure if oil collects inside this fitting if the PCV plugs in from below, or whatever so I make a clocking ring for it to get it back to near OEM orientation.
This is what these parts are for:
So the the first step is to center the PCV elbow on your large metal ring and mark 2 holes for the screws to attach it to the ring. Then screw the ring to the manifold using the 2 holes you just drilled and install the PCV elbow into the manifold (clocking it into the orientation in the pick below) and mark the second set of screw holes on the ring. This is what the ring will look like, you should have marked and drilled 4 holes:
Notice I have it slightly angled so the PCV hose attachment points a little to the rear, this is because the space is tight against the runner above the elbow for plugging and unplugging the PCV hose if the Elbow is perfectly upright, so I prefer to clock it a bit backward. (This will make sense if you look at the picture below.)
Once you have your 4 holes drilled you can use the stainless screws, nuts, washers, and nylon spacers to mount the PCV elbow to the manifold in the near factory orientation.
And this is the end result we are working towards for the PCV elbow install step of the swap.
Next up we are going to adapt your old PCV hose to fit the new set up. If you have a hose which only had one manifold attachment then it’s likely already good to go. All the ones I’ve seen have had 2 fittings to attach to the manifold so I’ve had to cut out the middle fitting and then rejoin the hose without it.
So turning this:
Into this:
I do this with 2 hose clamps and some “purchase by the foot” vacuum line from auto parts store. They keep it on a spool behind the counter so you have to ask for it. I used 3/4” vacuum tubing and a couple hose clamps. Just push the ends you are joining inside a maybe 6” section of vacuum line (they should fit snugly inside) and then use some hose clamps to seal it. This is the end result:
Only a few small details left and the N54 manifold can go into the car! The next step I do is I start transferring the junction box bracket and power wire brackets (the positive cables that pass over the engine attach here) from the old manifold. So just look at your original manifold and transfer as many brackets as you can. You’ll have to drill a few holes in brackets to get them transferred. Like the junction box bracket needs 2 new holes drilled in it but there is a place to mount it using the same screws under the N54 manifold.
Once you have transferred the brackets swap the MAP sensor from the top of your N52 into the top of your N54 manifold. This is the sensor on top at the rear of the plenum on your stock manifold which attaches with 2 screws. This will bolt right in using the same screws. **Do not use the boost sensor that likely came attached to your used N54 manifold, make sure to swap the correct sensor from your old one**
If you have a N51 congratulations, your N54 manifold is done and you are now ready to install your manifold in the car and build the Airbox to Throttle Body intake pipe.
If you have a N52 the last step before install is to plug this Vacuum Line Port on the front of the manifold next to the throttle body. The N51 has a line to attach here but the N52 doesn’t.
For this I just put some RTV (silicone might work also) on a small screw and just screw it into this hole. The plastic is soft and will accommodate most any small screw you have lying around. Bonus points if you use a stainless screw lol
For N52 your manifold is now ready to bolt into the car and proceed to the last steps, making the intake pipe to connect the Throttle Body to the Airbox.
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For this last step I used 3 pieces from Amazon which I linked in the post above, a 45* silicone elbow on the Airbox end, an approximately 3” long piece cut from the 3.5” ID aluminum tube, and the 45* 3.5” ID Elbow on the throttle body.
Here’s what I ended up with:
This is pretty self explanatory. I used 2 hose clamps on the TB end of the 45* elbow because it seemed to help make it fit better there. The 3.5” Aluminum tube can be tricky to get inside the 3.25” 45* Elbow. I sprayed some silicone lubricant on the parts and was able to get the elbow over the tube. If that doesn’t work for you maybe try heating the silicone some to soften it.
One of the swaps I did with my buddy recently he just mated the 2 silicones directly and left the aluminum tube out.
His comment was “I actually skipped the aluminum tube and just put one silicone piece in the other. Then I put a metal clamp around it to reinforce it from collapsing under vacuum.”
I felt the aluminum tube was needed to keep the silicone from collapsing but he seems to not be having any issues without it.
So there you go… Your N54 Manifold Install is now complete. Now install your tune and you should be good to go!
