Craig_D's Dual Cat SC Exhaust

[Craig_D]

Hi folks, I've gotten a number of requests for more pics and info about the dual Cat exhaust that I designed and had built for my '78 SC with SSIs. My designs were rough 3D estimates for the idea, but the real person who made it happen is a cage and custom exhaust builder named Hank Padilla. He and his team at Hanksville Hot Rods do great work building cages and exhausts for many Porsches along with tons of other cars/trucks.

The idea that I had (which isn't new, but I wanted to make happen) was that the space between the merge on a pair of SSI headers, and the inputs on a dual in/out Magnaflow style muffler had enough room to squeeze a pair of functional Cats. This way I can pass emissions and run clean all year round.

We ended up cutting the SSI headers just after the merge, adding V-band flanges, up-size adapter pipes (from 2" to 2.5"), Magnaflow stainless steel catalytic converters (spun ceramic, 2.5" with straight ends, OBD-II heavy metal), V-band flanges and then an 18" dual in/out Magnaflow muffler. It required a lot of mandrel bends and a lot of patience.

In the end, the exhaust passes Colorado emission, is lighter than standard 2 in 1 out sport muffler, and sounds like a German opera sung on the Mulsane straight.

Here are pics of the results.

Cheers,

- Craig_D

[Craig_D]

More Pics:

[Craig_D]

Even more pics:





Mocks:






The Sound Clip.

Cheers,

- Craig_D

[will hung]

Thanks for the pics Craig. I love this exhaust set up. Very clever, looks great and sounds great. A secondary benefit is that the cats are heating your heater air before it enters the heat exchangers.

[Josh D]

Truly the nicest concieved exhaust I've seen for the early cars. Great job. If only there was a larger market for it so one of the exhaust suppliers would pick it up to build and sell.

Enjoy the music!

[Nickshu]

Wow thats very cool! Nice work!!!

So far the SC passes Colorado Smog every 2 years without the CAT. It just passed again last week under the "fastpass" criteria. The guys who work at the state smog test station have not noticed yet. I think they see the O2 sensor (it's an 82) and assume that the SSI heat exchangers are CATs (or they just look the other way and check it off).

Nice to know there is a backup plan for when one of the smog techs finally notices and my SC gets "red flagged" in the state database.

[Quicksilver]

Did you ever run the car with that muffler but without the cats?
Just wondering how much the cats effect the sound output.

[fireant911]

Craig D.,
I must give you great praise simply for your interesting usage of Google/Trimble Shetchup!!!

[kodioneill]

Nice!! That engine is one of the most dry and clean from underneath I've ever seen.

[Iciclehead]

That is definitely the way to go....and I will end up going that way when my project gets to that stage.

Only question I have is whether anyone is aware of any physically smaller catalytic converters that might tuck in just a little better? Practically I wonder if a converter off of a small car currently in production might work - we only have 1500 cc of exhaust coming into each converter, so a pair of converters off of a 2 litre car should do the trick.

I also agree that'd be wonderful for our friends at SSI to do a small fiddle on the primaries to give a bit more clearance for the collector/converter combo - I would imagine that would sell to all us SC or Carrera guys. I know I will grieve when I cut up my brand new SSI's to do this....

Dennis

[Craig_D]

Thanks guys! Yeah Will, I'm getting some extra pre-heating down there.

Nick, it did pass Colorado emissions with no problem, and I'm hoping to pass the fastpass sniffer test so that I don't have to put my damn air pump on EACH YEAR (yes, older than 1981 is every damn year...hence this system If you get down to Boulder, we shoulder run some canyons.

I haven't heard it without the Cats on there, but eventually I'll get Hank to make me some track connectors and remove the Cats for track days.

Thanks Daryl, I work for Google and was the first QA engineer hired onto the SketchUp team after they were acquired by Google in 2006. Sadly a lot of my buddies left for Trimble, (I'm still at Google), but I talk to them all the time.

Engine is dry/clean only because Colorado is very dry..I didn't clean it. Well, not the bottom anyway.

Dennis, I worked with Hank (at Hanksville Hotrods) for a while on using smaller Cats, and those were the smallest that would actually do the job for the long run. A lot of the smaller Cats can get ruined easily after a short amount of time, and stop flowing (and working). I wanted power for years to come, so that was the way to go. I do scrape them every so often. heh heh

- Craig_D

[tirwin]

Originally Posted by Craig_D

Even more pics:

Is it just me or is your sump plate turned 90 deg the wrong way? I thought the drain plug is on the driver's side. At least that's the way mine is on my '83.

As one of the people who was asking questions, I can't wait to look at doing this project!

Thanks for sharing, Craig!

[Jdub]

Yes, that drain plug should be at the "West" (driverside) point - I would look into that and the condition of the bowler-type sump screen for any indents.

But that is one fine-looking exhaust. Nice job!

[Craig_D]

Huh! Well whatdya know?!

I never realized that. I have never personally taken the sump plate off...but I'll look into it.

The PO did some screwy things..turns out that I also have a nearly crushed oil return tube from the PO obviously taking the car to a place that lifted the car using the rocker covers (they're crushed as well, but you can't see it unless you're under the car). Since I'm about to do a suspension refresh, and I've decided to shed the rocker covers, I'll be getting new oil lines, so I can also remove the sump plate and rotate it properly. You can even see in my 3D SketchUp mock, that the SSI picture has the sump rotated as you say.

Thanks guys!

[gint]

That's nice work. I think I've seen your car at C&C, but it's been a while. Hopefully the weather is decent the first Saturday in January.

[Craig_D]

Hey Ginter, thanks! I made the November C&C and am hoping to be at the January with a completely new suspension, brakes, and oil lines! ...I'll be working my butt off on the rebuild over the holidays, otherwise I'll be in my girl's GTI.

At the last Boulder/Denver C&C, lots of folks came up to say that the exhaust sounded wicked. I went through the gears a bit before turning into the parking lot. I love the way she sounds now!

Do you usually bring your red 914-6? I love those...I'd like to have a black wide body 914-6 added to the stable some day.

[gint]

I was there in November in my zambezi 914. Just got the S two weeks ago last Saturday. I'll bring it January if it's dry out.

[gint]

[Craig_D]

Originally Posted by heaodfrant

I know I will grieve when I cut up my brand new SSI's to do this.

Well I had no reservations. I had bought a used, somewhat banged up but fully functional, set from a fellow Pellican, and we did the steps to make sure it would work before the cutting began.

Also, I still have the pieces that were cut off and could easily have the V-band flange welded on, to bring the SSI's back to fully stock function.

Not that I'm going to do that....I love this system!

[Craig_D]

Originally Posted by gint

I was there in November in my zambezi 914. Just got the S two weeks ago last Saturday. I'll bring it January if it's dry out.

Sweet!! I hope to see you and the S in January! Even if it's a bust, we'll have to set up a get together with just the Porsche crowd some time!