[justin_e92]

Hi everyone. Does anyone know the outer diameter of the stock or aftermarket N52 header/exhaust manifold tubes where the tube passes through the flange and mates with the exhaust port? In other words, I want to try to make my own headers and I need to know what size tubing to get. I read that they are 1 5/8" OD somewhere, but I would like to know if anyone can confirm this.

I will be working on the headers in a couple weeks and I want to order the tubing ahead of time, and avoid having to take the headers out, measure the tubes, and put them back in until I am ready to make the headers if possible. Thanks in advance!

[Taskmaster]

I have some stock ones at home I can measure for you.

[justin_e92]

Thanks, that would be great! If you could measure the end of the tubes where they come out of the flange into the head, then maybe get a measurement after that flange but before the cat, and then finally post-cat at the end that goes towards the secondary cats, it would be awesome.

As of now, I'm thinking 1.5'' OD 16 gauge tubing for the runners.

[PORTMOODY]

I have n53 ones as well I can measure.

[justin_e92]

Okay sure. I definitely would like the N52 header dimensions, so I can make sure the tubes I buy are right for my car, but it would be interesting to see if the runner tubes are larger for the N53 headers. I wonder if they have different exhaust ports?

[hassmaschine]

They are the same. As easy way to tell is to cross reference the part # for the gasket.
http://www.realoem.com/bmw/enUS/part...&q=18407530606

[justin_e92]

Ah okay, thank you.

[W37V]

Originally Posted by justin_e92

Hi everyone. Does anyone know the outer diameter of the stock or aftermarket N52 header/exhaust manifold tubes where the tube passes through the flange and mates with the exhaust port? In other words, I want to try to make my own headers and I need to know what size tubing to get. I read that they are 1 5/8" OD somewhere, but I would like to know if anyone can confirm this.

I will be working on the headers in a couple weeks and I want to order the tubing ahead of time, and avoid having to take the headers out, measure the tubes, and put them back in until I am ready to make the headers if possible. Thanks in advance!

Here you go man..

https://imgur.com/a/8OYWUnH#rbzqxtI

View post on imgur.com

[justin_e92]

Awesome! Thanks a bunch man. Time to order some tubing soon!

I'm a little worried about how much room there will be to work on piecing together the headers in the engine bay. I'm thinking of making a jig based off of the stock headers to make sure everything lines up.

[Taskmaster]

Are your making a custom set? Are you using a header calculator?

[justin_e92]

Yeah, I want headers on my car but don't have the money to buy them right now. Also needed a little project during my winter break from school.

No, I haven't looked at a header calculator. I figure if I use pipes with a similar diameter to stock or aftermarket headers, and roughly imitate AA or SS's design then that will work alright. I saw on AFE's website they use 16 gauge 1-1/2'' tubes, which looks to be about the same as stock, so it looks like I should be okay using that. I'll try searching up a header calculator for fun.

[hassmaschine]

The biggest variable you have control over is primary size and collector design. "equal length" is talked about a lot, but in reality, it doesn't matter as much as primary size and length, and usually you're restricted by packaging more than anything. There are basically no real truely equal length headers anywhere - and where they do exist, they are insanely expensive.

rule of thumb is don't go too big on primary size. you don't gain much power, but you do lose a lot of torque. I suppose in the end you're restricted by the exhaust ports on the N5x platform anyway, so all you can really do to improve is increase the length to the merge/collector and eliminate the cats.

[justin_e92]

Yeah, I figure BMW engineers probably did their homework on choosing the primary size, so I'll probably just stick with that - assuming the stock size is ~1.5".
I'm not sure if I should increase the diameter after the merge to 2.5" (I noticed the AFE race pipes are 2.5'") or just keep the stock size. It looks like stock ID is 43mm = 1.69" based on W37V's images - but it looks like it could be up to 1.75" because the caliper is slightly angled - so maybe I could get away with 2" pipe after the collector if I wanted to mimic the stock exhaust?

[justin_e92]

(Assuming 16 gauge tubing). But I'm not sure if the step-down in size at the from 1.88" (ID for 16 gauge 2" tube) to ~1.75" at the flange would pose an issue for optimal flow.

[hassmaschine]

Flow is meaningless. What you really want is velocity.. that's why primary size matters and "backpressure" is a myth.

After the collector, the exhaust size doesn't matter as much. You want whatever will keep velocity up without causing backpressure.

[justin_e92]

Okay yeah that makes sense, thanks! I have ordered primary tubing, collectors, and flanges to the post-header pipe. Next I will order 02 sensor bungs and gaskets/material for the head flange.

I won't be able to spend money on a tune until the summer, if then. I will definitely install my headers if and when they are complete to test the sound, but I don't expect any performance increase until it's tuned.

I would like to know, though, if driving around with my homemade headers without a tune will be harmful to my engine. I don't really mind if there's a CEL on, but I don't really want the engine running excessively lean or rich or something. Do you have any idea if it will be bad for the engine?

[justin_e92]

Oh, after some research I see that maybe the second O2 sensor (or wideband if that's what it is) feedback can be modified with a voltage divider to keep it in the correct range to avoid the CEL and possible fuel trim issues.

[PORTMOODY]

you can just add a spacer to the bungs and it will read fine.

[justin_e92]

Oh wow, I didn't know it was that simple. Have you used these for the N52 or do you know of anyone who documented using them?

I just did a google search but can't find anything for our car... mostly people asking if they work for the N54.

[Taskmaster]

Originally Posted by PORTMOODY

you can just add a spacer to the bungs and it will read fine.

Yeah, that’s not really true.