Alternative Stainless Steel Exhaust system – gauging interest

As some of you may have read recently I completed building a custom SS exhaust for my 3.5 motor with 5 spd. I am preparing for the final phase (replacing the lateral rear muffler and tailpipe section).

It has occurred to me that my system is different enough from the CK’s that there may be some market for having additional ones built. It would be easy enough to build a jig and perhaps fabricate a few of these using the 304 stainless tubing and 409 magnaflow components. See the following links for what I have built to date:

http://www.e9coupe.com/forum/showthread.php?t=11618

http://larsenarchitect.com/BMW/Sections/Exhaust/BMW Exhaust Frameset.html

Essentially I am thinking of the system comprising of the manifolds all the way to the tailpipe. Options might be to delete the catalytic converter, the heat shield, and/or change the length of the center resonator and rear muffler, and what pieces (besides the manifolds) to ceramic coat. Obviously the fewer mods the better from a cost perspective.

Here is a brief description of the components:

Manifolds: Cast iron from a 1985 m30 motor. These fit fairly well to the b35 head ports. They have the bendit of being able to receive the old style heat shield to the top of the manifolds (the cast aluminum ones) instead of the cheesy integrated gaskets. The manifolds look like the stock 3.0 ones, but have slightly larger interiors and a rotated flange.

Downpipes: 1-3/4” diameter SS 304 downpipes converging to 2-1/2” SS 304 pipe. Installed 02 bung.

Center section: consisting of flex coupling, short catalytic converter, and 18” x 4” center resonator. The catalytic converter really helps to reduce the noxious smell that comes out of these pollution-equipment-free engines, and does not really affect performance.

Rear muffler: 18” or 27” x 6” unit.

Tail pipe: 2-1/2” SS 304 stainless with the last section polished, perhaps with ringed end.

From a price point I could see these being in the $1,600 – $2,000 range ready for installation, not including shipping. Obviously, the target audience are for those with the 3.5 liter motor upgrade.

The current exhaust note sounds great, slightly throatier than the stock setup. I am not sure how it will sound yet with the new rear muffler (probably a 27” long unit – if I can make it fit). I may try the 18” unit to see how that sounds as well. I will need to get some videos so demonstrate this of course.

If any of you have comments, questions, or possible interest, please post here or PM me.

Thanks,

Exhaust options in SS

Hi Sven:

Look forward to hearing how this sounds.

Is there anything to be gained in running the pipe into the rear muffler in-line rather than entering it at 90 degrees as in the stock? Always wondered.

Doug

Doug,

The stock setup with the inlet pipe piercing the side of the muffler seems like it is the most restrictive piece in the system. When I had it apart I looked inside. Basically they inserted a pipe with a bunch of small holes in all sides. The end of the pipe is welded to the opposite curved sidewall of the muffler. So, the gases get dispersed in all directions out the small holes before making their way to the outlet side of the muffler.

Interesting stuff this is. There was a certain evolution to this project and it started over a year ago. The system I had on my car was in poor shape with a lot of sub standard work to say the least. Plus one of my down pipes had a serious ding....weird as it appeared to be done on purpose but for why? No idea.
I was considering different systems and talking to all that would answer my questions. The boys at "CoupeKing" at that time did not want to split anything up on their systems and would not ship to Canada. OK....now I am on my own. Judy Stahl was very helpful for specification as well as Carl Bennett at Korman. Lots of ways to go with exhaust and many differing opinions. Not much in the way of support here where I live shy of Budget Muffler. So research required . I also felt that a nice system could be built for reasonable $$$. I pre-paid and hoped a good used set of post 1988 down pipes for the 635 CSi to show at O2 salvage (thanks Marshall) This took nearly a year, they are rare. These are 2 inch and fit the two bolt style manifold. In the mean time, I bought a set of 1987 635i spec. down pipes with cat from a Canadian supplier, Bosal. They were cheap, so to speak, $240. The test fit was no good to the stock manifolds. So I preceded to cut and weld to make good. This we refer to as "Pipes 1.0" Basically 1 3/4 down pipes to a merge...1 3/4 to 2 1/4 with the bung just past the junction. This is as BMW designed as the proper position for the O2 sensor on the 1988-89 635i. Meanwhile, again, some headers showed up on 'da Bay....I bought these and had them ceramic coated. The so called "headers of mystery" Nicad has a set as well and I still have no idea as to the fabricator.
I can weld mild, no stainless...gotta learn.
Prior to install of the headers I did some testing and comparison, measurements as to have a base line. Please keep in mind that at the end of the day it is velocity of the exhaust gasses that is important and not necessarily the elimination of back pressure. I measured back pressure from the bung with a water manometer.
In conversation with Sven, I asked " why do you figure those '87 pipes did not fit? Seems to me the "clocking" of the bolt pattern may be different. Did they use a different manifold in 1987?" He says "I dunno....I thought all were same until the two bolt....let me find out" Turns out my intuition was correct.These are #808 286 808 here after referred to as the "808". Stock on my car was 603 250 603 or the 603. The two bolt is #816 286 816. There was in 1987 a change for some 8 months only, until the made the change to the two bolt ball and cone. Sven found two sets of the 808's on the 'Bay. Says "you buy one set I buy the other" " "Get a set of the Magnaflow #23556 and lets see" The trouble arose as these pipes I believe were designed for the sedan. Also that their jigs are a little off. Sven made the corrections as required.
Volume for the three as followed :
816....425 cc
808....350 cc
603....300 cc
As you see there is volume differences as to the cast manifolds. Air in and spent gases out. The normally aspirated engine needs a balance. Finding the right combination without benefit of 'dyno is a chore. Trial and error.
It is my opinion that these 808's are very nice. Even cast and porting vs the others. What Sven has done is the correct combination of the 1 /3/4 to 2 1/2 system using the 808 manifold applicable to the stock 3.5.
I did no back pressure testing for the 816.
The headers work for my car using 2 1/4 pipes and mufflers, 3.3 and stock cam. These have 1/1/2 tubes and "short" style. I did a reduction to 1 3/8'' prior to the merge to the 2 1/4 pipe. The manometer readings showed that "pipes 1.0" were "spiky" for lack of a better term. The headers were a gradual climb and the result was a little more back pressure at WOT. This leads me to believe that the headers were "tuned".... back in the day. Much as we did with motorcycle pipes, balanced for better flow. Similar to carb tuning to the bubble. The headers are more quiet than 1.0. Nice torque curve by my seat of the pants. Burble....certainly I will get questions as to why I choked it down a bit....that is another story and again, much research on the subject. My way and others will not agree. Too bad. I used band clamps as the same as the "coupeking" The V-bands are much more elegant.
A few still make new headers. Judy can supply from 1 3/8 to 1 5/8'' Mild to wild as it were. They are long tube design.
These are what they sell to deep pocket customers at Korman, cheaper you get from Judy. Ireland builds to 1 5/8 spec. and short tube, I dunno. The Dane's have the 1 5/8 and short tube....could work.
Be careful not to "over pipe" is my opinion.
My friend in Alberta has the 2 inch pipes from this project and will test further with the 'hypo 3.5.
In conclusion, what Sven is offering is a well engineered system, appropriate to the 3.5 in mild tune and at the cost of upsetting my freinds at CK, superior.

3"?

I have a pretty sweet set up for my rig, I picked mine up from Craig's list, someone spent a few bucks on it, and it came with a Stahl header all for $300.00, might be a tad bit to big but it's tig welded, made with aluminized mandrel bent tubing, two smaller stainless steel mufflers. Who ever made it knew what they were doing flawless work looks nice, might not last as long as stainless but gets the job done!

The exhaust on my new to me car is pretty shot and sounds not so good, and now the rear support broke and it is thunking around back there...

After reviewing this and every thread I could find, many like this one quite excellent, and based on experience designing an exhaust for a previous car, I am going to try another Magnaflow based system, hopefully with a deep tone like the Coupe King system, but quieter. Will be using dual resonance cancelling Magnaflows that will provide a crossover to hopefully help with scavenging. If this is too loud, may try to add another pair of the bullet mufflers. The only real out of the box thing I am doing is forgoing the transverse rear muffler and putting more muffler volume near the front, and add resonated tail tips to address raspiness. From Summitt, the cans and tips were $350. For you techno geeks (like me), yes, it does look an awful lot like 1/2 of a 60s/70s Ferrari V-12 system. Hopefully this will have a good result - will try to post a video in a couple of weeks.
Drawing not to scale.
Thanks.
<edit>
photo amended to show single rear pipe to exhaust tips.

Exhaust update

Ok. I finally replaced the last original section of my 3.0 exhaust with the 2-1/2" system. Photos and video links below. Per decoupe's inspiration I fit the 5x8 x 24"L Magnaflow muffler. The bottom of this hangs at a similar elevation to the stock muffler. In my case about 1" below the bottom of the differential (or 5-3/4" above the ground). The oval muffler fits well in this space, just slightly rotated and with an indentation for the differential mounting arm/bolt. The pipe at the end the of center section was cut off and rerouted to tie into the new rear section. I sanded and polished the very end of the tail pipe that will be visible under the bumper. I will post more photos once reinstalled on the car.

The sound is similar to the old smaller muffler. Not too loud - check out the two videos. When on the highway at speed the car seems to pull better. My imagination? maybe.

http://youtu.be/qndMn4zA_cY
http://youtu.be/cB2Hf7E8Vug

Photos

System installed

More photos with the final pieces installed on the car. Also welded up a jig for any future system builds.

Sven said:

More photos with the final pieces installed on the car. Also welded up a jig for any future system builds.

Click to expand...

Very well done!

SS Exhaust

Looks great Sven - the 120 into the rear muffler is a better solution than 180 and 90. Yours definitely has a deeper tone than the stock.

Although delayed by a move to Ohio, we finished putting on an exhaust system using Ireland s/s ceramic coated headers and a series of Magnaflow mufflers with period twin resonated Ansa-style tips. While not to everyone's taste the car is near absolutely quiet in the cabin except for some muffled mechanical sounds or a low growl at large throttle openings. Yet, one can roll a ball from one end to the other being a true free flow. I need to tweek the tailpipe positioning a bit in and up. but one the resonated tips make a difference and the twin tips are so 70's.

Since I like to take highway trips in the car, the combination of the smooth quiet exhaust and the 5 speed make it darn near perfect for me. A perfect Grand Tourismo.

Hi
I dont suppose you have a recording of what this exhaust sounds like ?

Hey Sven, you may have my solution here! Please see my recent posts on the my quest to find a more refined and sophisticated solution for my CC stainless solution. Do you think your Magnaflow rear muffler would work with the rest of my CC system?

@Sven Also did you ever go forward making a jig to make more of these SS exhaust systems?

Wayne, I assume you are talking about the Coupe King system? Too loud? I think my system has a slightly larger rear muffler so is quieter. You would likely need to build a custom pipe section from the center resonator to the rear muffler. Can you tell me the sizes of the CK stuff?

Stan, I do have some jigs although I have only made one other system for a local coupe.

Howdy Sven- I have 4-5 sets of CK and W&N exhausts at the shop. Call for measurements

Hey Sven, attached is a photo of my complete Coupe King system including stock B35 exhaust manifolds. The Magnaflow rear can is about 18" long, 6.5 wide and connects to 2.5" pipes. I think the Magnaflow can is a racing muffler with very little baffling. My issues are more the quality of the sound and not necessarily the loudness. Stock is too quite for me, even when I removed the 2nd muffler from my stock exhaust years ago before the new system. I'm looking for a more sophisticated, smooth and refined sound like yours. I also don't want to mess much with my back pressure, more or lesss, as the car is running so well now. Doug McKenzie's is nice too - he has the W&N system.