Just completed full custom exhaust build, I'm exhausted (literally and figuratively)

[BMW540san]

Let's start by saying don't do this at home if you have any sense. But if you're 47 year old kid trapped in middle age body, do it by all means.

Let me also say that there is nothing wrong with factory OEM Exhaust on E39 series, regardless of model. If anything, it's overbuilt and it will easily last the life of the car.

My reasons for build like this are several: Sound, weight loss and extra HP. Also, I did thorough research and didn't just wake up one morning with a plan. While OEM exhaust system is built to last, it's extremely heavy and crushed bent at places. The reason for extra weight is that front part of exhaust system is double walled, probably so it retains heat for emissions purposes.

As far as sound, I simply refuse to chop off muffler, resonator or whatever. While people do that and it sounds good to them, I like the different approach (yes, it's many times more expensive).
Speaking of HP, I'm aware that it's probably minimum but it wasn't my main goal anyway. I just wanted to do put final touch on my recent build
https://www.bimmerforums.com/forum/s...swap-on-my-528 with proper high flow exhaust since I installed higher HP / torque S52 engine and left the factory exhaust designed for M52 engine.

So, let's start:
One of the biggest mistakes a lot of people do is to increase tubing OD on exhaust system and think they got extra HP. It's just the oposite in many cases. I'm not going to hold a lesson in exhaust science but I've read plenty of articles written by real experts and concluded that stock E36 M3 tubing OD is plenty big and there is a delicate balance of tubing OD vs. back pressure etc...

So, I've done dual 2" tubing OD from Supersprint headers (they are 50mm OD which is almost identical) and then went to single 2.5" OD tubing. I positioned all the components in aprox. locations where OEM components use to live for obvious reasons.
While I did research before my build, the luck still played a role. What I mean is the fact that instead of 2 factory resonators (small one after cats and Y shape monster that weighs a ton) I only installed Vibrant Performance 12" straight through resonator.
Well, it worked! Sound is awesome and no drone whatsoever! Another nice thing is that it's only loud when I really get on it which is what I wanted. I live in nice subdivision and I don't want to be "that guy". I'm sort of "that crazy guy with lift" already but anyway...
On that subject, I can't say enough good things about Vibrant Performance brand: Everything I got is top notch quality: straight tubing, mandrel bend pieces, 2 into 1 collector and resonator, all of them are T304 stainless steel.
Which again brings me to next subject: Everthing was TIG welded and back purged. While I do take credit for designing the exhaust, my neighbour did the welding and he did awesome job.

And this was anything but easy. There was a lot of measuring, cutting, grinding and welding as we basicaly built the whole thing using set angle mandrel bend tubing. It would have been much easier and less welding if we had tubing mandrel bender at site but good one probably cost like my whole car.
After everything was welded and before first start I cleared all of the ECU adaptations with my trusty AutoEnginuity scan tool and set it to watch fuel trims.

I'm happy to report that after engine has warmed up, the fuel trims in closed loop and when idling are almost zero % which is excellent news.
I've driven it about 50 miles now and no CEL and I'm very positive that midrange torque is up. The S52 is torque engine to start with but there is a noticeable difference now. Yes, the only true way to know the HP / torque gains is dyno before and after but I've owned this car for 17 + years now and had S52 in it long enough to tell the difference.

The final touch was to put some heat shield on headers. While I hated to cover work of art, my number 1 goal is function, not the looks.
I've had this heat insulation sitting in box for 2 years and I've finally put it to good use. It's extremely high tech stuff made in USA and I verified their claims today: 58F cold, 130F peak temp on shield while 500F + on headers, numbers don't lie.
I purposely didn't use wrap or heat shield all around but only on top as I didn't want radiant heat killing 2 rubber brake lines and ABS controler.
I have some insulation left and I will probably install it where tubing goes under driveshaft flex disc.

I forgot to mention that ECU I had custom programmed for S52 engine has built in delete for Secondary Air Injection (Supersprint headers don't have provision for it as factiry headers do) and the rear O2 sensors delete which made my build easier since I didn't have to drill the tubing and then weld O2 bungs after cats.

So, this is my exhaust now (front to back):
Supersprint headers (equal lenght runners) - dual 2" OD mandrel bend tubing - 2 x 50mm HJS cats (high flow 200 cell metallic, made in Germany) - dual 2" OD mandrel bend tubing - 2 into 1 merge collector - single 2.5" tubing - 2.5" resonator - Remus muffler (previously installed).

I've also designed this exhaust system for ease of removal: 2 x Butt-Joint clamps at headers and 1 x But-Joint clamp at muffler plus 4 bolts at OEM mid plate support and it's out.
This section in OEM flavor was over 70lbs while mine is around 20lbs. The total weight saving is around 80lbs considering that Remus muffler is like a toy when comapred to factory "dual scuba tank" muffler and Supersprint headers are considerably lighter than OEM headers.
Including the S52 / 5speed swap I'm at 150 lbs + weight savings: auto tranny is considerably heavier than 5 speed, plus extra fluid, cooler and lines, tranny computer etc...
I'm not building lighweight racer but losing weight equals gaining HP in some respect. I just did 15 miles on back roads and while it's not 540 / M5, it handles considreably better due to less weight / rack & pinion steering and it's plenty fast for some fun.

To sum it up:
I did this because I wanted to and I'm proud with final result: I improved the sound, lost considerable weight and gain some HP and torque.
Is it cost effective, hell no!
Does it make me happy and am I proud, hell yeah!
Some pics in 2nd part:

[BMW540san]

2nd part:

[Liquidity]

Holy crap how long did you spend typing that

[BMW540san]

Holy crap how long did you spend typing that

About 6 pack of good German beer long

[Liquidity]

Well it took me about 1 shot of American white lightning to not read it.

[BMW540san]

Well it took me about 1 shot of American white lightning to not read it.

Glad to hear that. I'm totaly fine with you not reading it.

[R Shaffner]

Impressive, as usual. Admire your work.

[BimmrMeUpSnotty]

Well it took me about 1 shot of American white lightning to not read it.

What a speed shooter you are.....

I had ten shots of Cuervo by the time I finished reading it all.

Nice job on the exhaust!

[BMW540san]

Impressive, as usual. Admire your work.

Thank you. I enjoy a challenge and this was one for sure.

[JimLev]

About 6 pack of good German beer long

+10 on the German beer.
I see the addiction continues.
You did a great job.
I’ve used Vibrant stuff on my 540 and on the hotrod I’m building, good stuff.
If the county ever starts with emission rules (none here now) and I have to get CAT on my ’33 I’ll get those HJS.

[philly98540]

Round 2!! You got this one right. Nice details and clean welds. HJS are the best aftermarket performance cat. Mine are still working good. Post up a sound clip if you get a chance. I still can’t believe you did this job again after realizing how much effort it takes. Congrats

[pietern740il]

Thank you for sharing, I can image it sounds excellent as well. Great work

Question: how did you attach the heat shield and how far down did you wrap it the headers?

Sent from my Pixel 3 XL using Tapatalk

[BMW540san]

What a speed shooter you are.....

I had ten shots of Cuervo by the time I finished reading it all.

Nice job on the exhaust!

Thank you! Cuervo goes well with it indeed.

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+10 on the German beer.
I see the addiction continues.
You did a great job.
I’ve used Vibrant stuff on my 540 and on the hotrod I’m building, good stuff.
If the county ever starts with emission rules (none here now) and I have to get CAT on my ’33 I’ll get those HJS.

Yes, addicition is strong but I get a good high every time.
HJS is simply the best quality cat in the world, period. Price surely reflects it too, lol.
They are not widely avalaible here other than in high end builds from Fabspeed for Mclaren and such but then they cost like my whole build and then some.
The ones for 540 and M5 I sourced from German Amazon and these I got from reputable place in UK.
If you ever go that route, email me and I'll lead you in the right direction.

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Round 2!! You got this one right. Nice details and clean welds. HJS are the best aftermarket performance cat. Mine are still working good. Post up a sound clip if you get a chance. I still can’t believe you did this job again after realizing how much effort it takes. Congrats

Thanks.
Nope, round 3 (540 and M5 rounds 1 and 2), lol.
As Jim said it's addicition for sure. Yes, it was complicated but learning from 2 previous rounds mistakes definitely helped me in this build.

[BMW540san]

Thank you for sharing, I can image it sounds excellent as well. Great work

Question: how did you attach the heat shield and how far down did you wrap it the headers?

Sent from my Pixel 3 XL using Tapatalk

Thank you.
I used stainless steel wire because it's thin and strong. You just poke a small hole and twist it on the bottom side for clean look.
I've only covered the top of primaries down to where they merge since this is sort of temporary in order for me to test the manufacturer claims.
It's really high end product and they have some good videos too:
https://www.heatshieldproducts.com/heatshield-armor

[philly98540]

Did I miss the M5 job? Anyway, your getting good at this now. I take partial blame for getting you started on this exhaust DIY stuff. Difficult but very rewarding.

[Kenny1958]

That looks great!

I need to do summat like this for the 540.

[E39 Newbie]

Very nice. Thanks for all the pix.

[scubajim20]

Beautiful work, wish I had the skills.

[BMW540san]

Did I miss the M5 job? Anyway, your getting good at this now. I take partial blame for getting you started on this exhaust DIY stuff. Difficult but very rewarding.

Yeah, because I posted it on M5 forum. I can only blame myself as it's something I truly enjoy doing.

[BMW540san]

That looks great!

I need to do summat like this for the 540.

Thanks! Fair warning, this is quite complicated and expensive build.

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Beautiful work, wish I had the skills.

Thank you. I do have to admit, this build tested my skills for sure.

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Very nice. Thanks for all the pix.

No problem, glad to contribute little bit.

[demetk]

Nice work. Two questions.

Is purging necessary?

Are you getting rid of your old headers?

[BimmrMeUpSnotty]

The purging is to give you a much cleaner weld.

[BMW540san]

Nice work. Two questions.

Is purging necessary?

Are you getting rid of your old headers?

It's basicallu to have better looking and stronger welds. If not purged the weld inside can be weakened by oxidation.
Sorry, I already gave them to my neigbour to be scraped.
They're identical to M52 headers and nothing special (unequal runners, crushed bends etc...) so I thought there would be no interest.

[JimLev]

More info from a hack TIG welder........
Purging with argon prevents a build up of chromium carbide precipitation also known as “sugaring” which takes place when welding stainless steel. To keep this part of the joint back side of the welding area you purge it with pure argon to keep moisture and oxygen away from it. If you don't do this the chromium burns out of the metal making it susceptible to corrosion. If the build up is thick enough it can effect the exhaust flow.