Building yet another exhaust for the M6

[Da_Hose]

Ok, so first things first. The State of California is a pain in the ass when it comes to smog and my registration this year requires a smog. I got the DMV fees paid, but had to do a fair bit of digging to try and replace my failed catalytic with something that would pass. Turns out that Catco has FINALLY gotten some catalytics CARB approved. However, my VIN calls for dual cats and that means I have to redesign my exhaust .... again.

The really big deal here is that using Ca. legal cats. means this is going to be the final iteration of the exhaust for my car. Since that is the case, I thought it would be a shame to redesign the whole shebang and do a poor job. So I ordered a bunch of stainless steel parts and am building a 2-1 system that uses an x-pipe as the merge collector for the 02 sensor. The final configuration is 2" pipe at the header flanges into an SS x-pipe with O2 sensor bung welded in. Then the dual out goes into parallel 2" catalytics, with a y-pipe going into a 3" SS Moroso spiral flow muffler. There is still a small section of aluminized pipe that goes under the subframe and connects to the SS Flowmaster DBX muffler and finally a polished, slash cut 3" SS exhaust tip.

I still have to replace that center section of aluminized pipe, but I don't want to slow down and replace that as well. Cutting/shaping stainless curved pipes is a bitch without a large bandsaw and disc grinder. I'm just going to leave that center section until the spring.

The other big deal is that this is not the first SS project I have worked on at home and although my little Hobart MIG is a great machine, I am not satisfied with the way it welds SS. My M6 deserves a high quality finished product, dammit. I decided it was high time I bought a TIG welder. My choice is the ThermalArc 95S. It gets really good reviews from both hobbyists and professionals and you can find online videos showing great finished welds. The 95S is an inverter based, scratch start machine with an air cooled torch, but it can't do aluminum. My local welding shop also highly recommends the 95S as the perfect machine for the home welder who doesn't need to work with aluminum. I wanted to buy it from my local shop (support your local businesses folks), but he hasn't had one for over a month and his supplier said he couldn't get it to him before Friday (which might actually mean next week). So I went online and found it on Amazon for $429 shipped. Next day shipping upgrade was only $22 more.

I will certainly update this thread as the final exhaust comes together and include first hand feedback about how the new welder works out.

Jose

[hornhospital]

I'm really interested in how it works for you. I was the shop welder for almost 28 years, and almost all of what I welded was stainless or more exotic metals (Titanium, primarily, if it wasn't stainless). Several years before I retired I bought a Miller TIG machine (almost the same as I had at work) and have been really happy with it....but it was $1660 wholesale. If I had to replace it today it would be more that $2500. I couldn't get by with a machine that won't weld aluminum, but having one strictly for stainless is intriguing.

[Da_Hose]

I am certainly no expert welder, but I can TIG SS better than I can MIG it. I don't do a lot of aluminum stuff at home and with a small lathe and mill, I can make an awful lot of the small pieces I need. When I make bigger stuff, its pretty much all steel. I rebuilt the cabover in my motorhome and it was all steel, but I understand that some of the newer ones have more aluminum inside. If I had a 5th wheel or trailer, I would be much more concerned with being able to do aluminum.

At the price, having a steel only TIG makes sense for me. How do you feel about an aluminum spool gun, Ken? I have seen some folks modify their Hobart 140/135 MIG machine to use a spoolgun with aluminum wire. There is a cool how-to on youtube of a guy who modded his 140.

https://www.youtube.com/watch?v=19_KAOwRGf4

Jose

[hornhospital]

A 140 is too small for the aluminum castings I weld. My 180 Miller is barely large enough for the heavy air horn manifolds I weld together and restore. A spool gun would be nice if I had the amperage to weld thick material. Aluminum takes a HUGE amount of electric current to heat it sufficiently to weld.

www.airhornhospital.com will give you an idea of what I do. A 10 pound manifold casting is a challenge to weld. This manifold was cut apart by the previous owner due to it being clogged with compressor oil and dirt. I was tasked with putting it back together. It took about 12 hours work to weld, grind and reassemble this horn. (sorry for the off-topic, but this'll give you a better handle on what welding aluminum is like)

[Masked Man]

Jose?

You crack me the hell UP! First you poo poo your abilities with a welder then launch into a discussion of Hobarts, MIGS, TIGS, 140's aluminum spools, etc., etc. And Ken? JEBUS, that diesel locomotive horn chime must weigh a couple hundred lbs!

I'ma just sit back and listen to ya'll discuss shyte I have NO knowledge of. And definitely pick your brains if EVER I need to weld a-n-y-t-h-i-n-g.

Keep the shiny side up

Phillip

[Da_Hose]

Glad you're enjoying the show, Phillip.

I just know there are folks out there who are true artists at what they do, so I try to keep my own abilities in perspective.

Holy, cow Ken! Why would you cut up horn manifold like that? I would think that an ultrasonic, solvent bath and then maybe a mild abrasive air passage blasting would allow cleaning without cutting it up. Aluminum sure is one hell of a heat sink. That's some nice work you did on that. Can't really even see the weldments. Good to know a 180 can handle big castings. I'll keep that in my hat.

Although I don't ever see myself welding 100 lb. aluminum air horn castings.

Jose

[hornhospital]

that diesel locomotive horn chime must weigh a couple hundred lbs! Phillip

That assembled horn weighs about 45 pounds. The manifold by itself is about 10.

I wish we could carry on this conversation in the Saloon forum. I love talking about what I do, but this is the Engine - Mechanical - Electrical forum, and your exhaust project/new welder discussion fits there. A discussion about air horns doesn't.

[Da_Hose]

I got the TIG welder today as promised. It comes with a large (1/8 ) and small (3/32) tungsten. I also picked up a cylinder with argon and some new tig gloves. The welder even had a nice ball cap in the box.

I set up my workspace on the hood of my 2002 and hope to start working tomorrow. Assuming my back stops hurting, of course.

Jose

[GazM3]

Hey there.

Why are you going to a single 3"?

The M30 based engines love dual exhaust pipes the whole way. A dual 2" would be better. Perahps an X merge (or even better an elongated x merge) would give a nice lift in torque also.

[Da_Hose]

The single pipe is for a couple reasons, Gaz.

First off, I REALLY like the tone. I aint gonna lie. At 7000 RPM the S38 sounds BONKERS through a single pipe.

In my case, the PO had literally put a straight pipe on with a straight through muffler. HOLY COW that was loud and it had a drone at city cruising speeds that would try to shake your soul out right out through your butt hole.

So the first thing I did was play with mufflers/resonators to get to the tone I wanted. I ended up using a Flowmaster DBX muffler (dual reversion cone internals) with an inline Moroso spiral flow and dual resonators to kill the drone. That kept a low grumble at idle, got the db's and drone down where I wanted and left just enough bark on decal to make it sound like a supercar.

Since the rear section is already 3" and I really like the look/sound of the single pipe/muffler at the back, I decided to keep the sound dampening/shaping pieces but had to add Ca. legal catalytics. It's interesting to note that the factory system is basically an x-merge collector feeding into the catalytic anyway, then it dumps out to dual pipes from the actual catalytic elements back. So the system I am building now is different from after the catalytics, but the same as OEM up to and including the catalytics.

As to single vs. dual pipes in general. If you look at the M1 procar, it actually runs the same headers I have, but they dump into a gigantic (maybe 4") single pipe with what looks like a catalytic at the end. I am assuming the catalytic is to burn off excess fuel when coming off throttle and to accelerate final exhaust speeds. If that is the case, then I was comfortable using a larger diameter single pipe as it will retain more heat at mid-pipe than a dual pipe setup. I know the BMW brain trust says that the dual pipe is better on paper, but I certainly don't feel lacking in power. Although, I will say that I haven't driven a stock M6 and mine side-by-side or seen dyno. sheets concretely illustrating the performance differences.

Jose

[Ralph in Socal]

The single 3 inch pipe also has more cross sectional area than 2 X 2 inch pipes so it will provide better flow. 12.5% greater X-section by calculation.


Ralph

[GazM3]

Fair enough. Id imagine the note through a single 3" would be pretty good but every m30 based setup I seen go to single 3" seem to lose some power/torque under the peak. Maybe I'm influenced by my engine builder as he thinks a single exhaust on m30 based cars is work of the devil lol.

As for having greater x-sect that would be of more benifit earlier down the exhaust line where the exhaust is warmer and has more specific volume. As it cools down the line then the need for greater x section is not there.
Where I think you would pick up power is making the pipe dia 2.25" from the collector to the cats and from the cat exit run to a merged single 3" or continue with the dual 2.25".

Arni (that chap who has all those m88 & s38 engined e24/e28 runs 2.5" from the collector then reduces down for memory to dual 2.25". He swears by this modification. Most of his engines are fairly modified. Besides dual 2.25" could easily support 350-400bhp.

[Da_Hose]

Hmmmmmmm......... I'm guessing that Ari doesn't use catalytics on his 2.25" exhausts.

You really need the catalytics as close to the collectors as you can get them or they don't heat up enough to do their job. I used 2" tubing off the collectors and I can BARELY make it all fit with enough room for the catalytics. If the pipes were thicker, I would have had to do something totally different and fabricate an H-pipe instead of a high flow x-pipe.

With how I put things together, I have a curved section of 2" pipe feeding a 2.25 x-pipe and that feeds the pair of 2.5" catalytics. I hope to do the final welds this weekend. We'll see how the weather treats me.

Jose

[Da_Hose]

Hey, folks. Another update on the project.

I have been battling constant rain days that kept me from working on the car, so I was in a hurry and didn't take final assembly pics. However, the exhaust is done and mounted.

One of my concerns with the new setup is that I was losing both inline resonators and didn't know what would happen as they help dampen the drone. The catalytics have mellowed the tone a little as I had hoped and the sound levels are no louder, maybe even a little bit reduced.

The collector to x-pipe section is the most difficult part to get right. I had to do a bunch of gusseting on the pieces I had and really struggled under the car to get angles correct, but it did finally come together. Now that angles and lengths are good, I plan to re-make the collector pipe section once I have my 2002 running. The setup seems to work just fine, but I really want this to be the last exhaust for the car and it bugs me to know that the front section isn't exactly what I want. Even if I (or anyone else) can't see it.

Come the summer (sunny days and 4 day work week), I will change out the last pieces of aluminized pipe in the rear section and refine the pipes feeding from the collectors.


While the exhaust doesn't seem to be rattling at all, I did replace the driveshaft at the same time and I can hear it hitting something as it rotates. I will have to get underneath again to confirm what is making contact and what I can do about it.

Jose

[orlando]

Hi Jose,

Rain is no excuse for the pictures, haven't you heard of underwater cameras? We want to see pictures!!

Have a great Christmas and a fantastic New Year!!

Orlando.

[Da_Hose]

Yeah .... super pic. fail. I'll get some pics. when I put the nose in the air tomorrow.

On the way home I paid really close attention to what was going and I realized that the rattling under the car probably isn't the driveshaft. The rattling goes away under power and comes back when I let off the throttle. It seems most likely the new exhaust is touching the body. There is precious little room to get the pipes curved around from the headers to the catalytics. You have to make a really tight radius and pass under a corner of the transmission mounting bracket. I think I cut it too close and when under power, the engine rotates to the right, which moves the pipes away from the bracket so it won't rattle. Under engine braking, the whole thing rotates the other way and the pipe makes contact with the corner of the transmission mount bracket.

I will update when I have more information.

Jose

[Da_Hose]

Today I finished the exhaust fabrication work.

I looked closely and saw a spot where one of the primary tubes looked to be contacting the transmission bracket. I very lightly relieved it with a small ball pein hammer and added a shim between the support bracket and outer primary tube. That rotated the inner tube slightly away from the bracket. Now there's a good 1/8" of clearance. I also noticed that the heat shield on one of the catalytics was buzzing and relieved the contact areas to get rid of the buzz.

The exhaust is buzz free and should pass smog. I also has reduced the drone and volume levels. Here are some pics of the setup.


This is a view of the collector to x-pipe section. The x-pipe connects right to the catalytics.



This is a view starting at the back of the x-pipe. The catalytics connect right to the x-pipe and then a y-pipe transitions into the new SS Moroso spiral flow muffler. The spiral flow uses a v-band flange to connect into the rear section.



This is a rough panoramic showing how it all flows from part to part.



Jose

[orlando]

Art work!!

[Da_Hose]

I appreciate the love, Orlando. Welding the insides of the pipe sections at the catalytics and x-pipe input was tough. There isn't much room in there to work.

I really like the overall design, but the input pipes were really hard to get right. When I redo the input pipes the welding will be much cleaner.

Jose

[wjtesquire]

I just spent most of the day working on my exhaust so I can appreciate the fabrication. That is some nice work!

[Da_Hose]

I have a very positive update about the exhaust. I took the M6 to be smogged today and it passed with flying colors. The catco catalytics were just the ticket.

Jose