SSI and dual cats - It's possible

[Marwil]

First, I'm terrible welder with stainless, just saying. I know I should TIG, but don't have the skill yet. I was MIG welding outside at -5ºC with a windchill and shivering but I want it ready to try out as soon as the snow and salt are gone. Ill' be posting some pictures now that I have all the requisite excuses out of the way.

I did not want to cut my SSIs - too expensive to replace if I frig it up. After looking at Craig_Ds system with cats and a Magnaflow 2 in 2 out I was fairly convinced that I could squeeze in some cats if I could find a muffler that was short enough. So I bought some parts and started visualizing...... for hours, taking measurements, visualizing some more and built a positioning jig based on my measurements. I used my positioning jig set up the cats and turns so that they would feed into the Magnaflow properly.

I now have a prototype system roughly fabbed up and it fits!

More pics and info to follow.

[DaveMcKenz]

That looks very good. The welds can be perfected, but great packaging. Curious on sound, performance etc, but I bet it's very good.
Thanks,
Dave

[matthepcat]

Great concept. Can't wait to see and hear it installed. I have been interested in a CAT solution for my car as well. Even just some high flow 200CEL cats would be great to reduce the stink.

[Bob Kontak]

Cats need to be pretty close to the combustion exiting the heads.

The SSI's are way different than my 81 exhaust that go forward first then backwards. Oh, and sideways for the right side.

Get that thing on there and use a laser thermo to determine in vs out temp.

[Marwil]

Just a rough 3 minute firing, but it is a deeper sound not nearly as raspy as the 2 in 1 out Dansk style I had on before. The motor winds out pretty quickly and settles down quite well. I'm curious about drone though - I won't really know until later in the spring. I'm pretty busy teaching for the rest of the week and away escaping winter next. I might get some time in welding and dressing the welds later this week.

Here's a bunch of photos of the process. These photos show the jig and set up for the left side. The upright was flipped to position the tight side. The upper end of the cat outlet was composed of 3 smaller segments of 2.5" id cut at angles of about 15º-20º to bring it to horizontal to feed into the Magnaflow crossflow.

[Marwil]

Once I get it all set up, I will do a temp check. I do know that the cats got pretty hot pretty damn quick!

[Bob Kontak]

Originally Posted by Marwil

Once I get it all set up, I will do a temp check. I do know that the cats got pretty hot pretty damn quick!

Outstanding.

[MARISOL78sc]

Interesting to know the end game, Do you need to pass smog? Looking for more low end torque? Decrease level of unburned fuel for environment sake? I have a 1978 Sc and the Cat is way beyond working as many are after 20 plus years, just trying to get a feel for the why,
if sniffer test is not in the equation as this would never pass a visual by someone who knows in a state like Cali that does a visual..nice fab work though!

[MARISOL78sc]

BTW, what cats are you using? And what cell, like the ingenuity!

[Marwil]

I don't need to pass smog as it is exempted here in Quebec but want to do my part and run cleaner. The cats are Magnaflow part # 59975 EPA compliant pre-OBD II spun cats with 2.25" inlets and outlets. They are 200 cell metallic substrate good for 200 hp each with a max engine size of 2.5 L.

[DaveMcKenz]

I'll buy one when you go into "production". Great idea. I have the same feelings you do about cats on my car. I don't like the smell, and would like to do my part to run clean.
Keep up the great work.
Thanks,
Dave

[Marwil]

I now have the system installed and running. Butt dyno says I'm making more power, particularly above 3500 rpm. And, it is definitely cleaner, the gassy odour is long gone. The power is about the same down low but get your foot in it and you can feel the surge at 3500. Sound above 3000 is glorious! In fact it is quieter in the cockpit above 3000 than below - which brings me to the idea of drone. I had a vague notion of what people meant by drone; I now have a very real, visceral, deep and resonant lived experience with drone.

Most enjoyable option is to stay north of 2800 rpm :-) I am starting to investigate how to mitigate the drone between 2200 and 2800 rpm. I am considering options such as the Dynatech Vortex (might have to fab my own as the smallest they may is for 3" ID), Quiet Riot baffles, installing side-branch resonators or installing a vacuum operated cut-off for one outlet. Capping one outlet manually, then removing is not a practical option. I do like the system for the power and the sound but want to keep working on reducing the bugs. I will try to post a video/sound clip at some point.

If you have some suggestions for drone I would be happy to hear them - while I can still hear :-)

[VFR750]

Was that a cross-flow (x flow) or a parallel flow muffler?

Great concept.

Drone is an amazing thing. Hopefully you’ll find a reasonable solution.

[Marwil]

The muffler is a crossflow with 2.5 inch inlets and outlets. The body is 14 inches long.

[Bill Verburg]

Here's an SSI +dual cat setup I ran way back in the mid '90s, it worked fairly well too, the exhaust was noticeably sweeter w/ it than w/o

[Marwil]

Thanks for the photo and your input Bill. I’ve this photo before as I was planning my system. Did the cats get hot enough after the muffler to do their job well. If they do then your set up would be much easier to fabricate. What was that set up like for drone?

[Bill Verburg]

Originally Posted by Marwil

Thanks for the photo and your input Bill. I’ve this photo before as I was planning my system. Did the cats get hot enough after the muffler to do their job well. If they do then your set up would be much easier to fabricate. What was that set up like for drone?

I'm sure that they didn't warm as quickly as the ones the factory puts closer to the exhaust port but they did sweeten the exhaust as well as the stock Audis I owned at the time, at least to my to my nose.

No drone, the muffler was an early version of the current B&B design w/ a smaller outlet hole on the right side, you never see the smaller hole because the tips cover all that.

Laws changed and I never had to get a sniffer test, so sold it long ago.

[matthepcat]

Looking forward to some installed pictures and a drive by video!

Sign me up if you intend to make some more.

[Marwil]

Couldn't drive the car, the sound was that intense. Read a lot about capping one outlet and then thought about a vacuum operated cutout on the right side. I've tack welded a cutout to the right side and the resonance has dropped significantly. It doesn't open up until you open up the throttle. I hope to get it out for a test drive tomorrow to see how it performs on the road. If it works I will weld the outlet back and run with it. Here's an initial pic of what's going on with the right side.

[matthepcat]

Interesting, so the exhaust would be forced out of one side with it closed and fully open at full throttle? Would be interesting to do that same with a toggle switch to choose "open or closed".

Something like this: https://www.summitracing.com/parts/dou-dec250a-1