Planet-9 Porsche Forum banner
  • NOTICE - Before adding photos to posts on Planet-9, please review: Posting Photos on Planet-9

Simple & basic cat-back exhaust build

9K views 35 replies 7 participants last post by  Plainsman 
#1 · (Edited)
As you longer-time members may remember, I've been working to quiet the drone of my cat-back borla exhaust for 987.1 - and my last word on it is I'm finished and it's still too loud for my taste.

Since I have a few past attempts at different tip configurations on the shelf I decided to go back to the pig-snout I built from a 2--->1 merge collector framed by the trapezoid stock CS tip surround ... I wanted the 2 cylinder banks joined to reduce drone and enable some exhaust gas scavenging.

The main challenge is finding mufflers which would fit and could be joined by off-the-shelf bends and some tube reclaimed from the factory CS exhaust, gathering dust since 2010. My fab skills are not great.

The Plan was to build it on the car, tack-weld the pieces together and then have it welded properly.

After looking at a *lot* of muffler brands, Googling until my fingers were blue in the face and reading Amazon reviews I decided on a pair of Flowmaster HP2 Shorty mufflers (12" long body) and two Vibrant Performance ultra-quiet resonators - one of each for each bank of 3 cylinders.

The pieces ...
Tip:

Font Pipe Auto part


Muffler and resonator:
Land vehicle Vehicle Car Race car Sports car
Auto part Cylinder Muffler Bicycle hub


The HP2 would extend straight towards the rear bumper cover, a small radius 90 degree bend would follow and the the resonator would attach to that - perpendicular to the long axis of the car ... each side would then terminate into the Y-collector / tip assembly.

Auto part Vehicle brake Wheel Brake Tire
Auto part Muffler Exhaust system Pipe Automotive exhaust


And the result:
Auto part


more details in the next post - stay tuned!
 
See less See more
6
  • Like
Reactions: Wanderer
#32 · (Edited)
About that 1/4 wave resonator I added ...

Still at it. I had to do some work on the center section where I'd tee'd a 1/4 wave resonator near the tip. I had left a telescoping+capped alum I tube terminating this resonator and had left it alone as it seemed to do nothing for the drone.

My previous attempts had been to go longer with this tube and got me nowhere. W.T.H. ... I wasn't getting any results, so I shortened it by about 3", so that it extended to the outer edge of the muffler it was mounted to.

And I have a modest reduction in drone. Worth a mention, mainly because I'd lived for 8 months with it droning away at the prev length. The result holds, so far, in cooler 30F degree weather and could change with the air temps. ... mmmv ...

... W.T.H. ... It's not a huge difference but some of the edge has been taken out of the drone. A resonator needs to be farther upstream to be more effective but I just can't see how to do it in the space we have.

I've turned my work to active noise cancellation. Small computer driving a car subwoofer and I have a basic system which shows good cancellation of a simple constant 100Hz tone. This on the bench without yet handling all the corner cases real operation in a car will require.

But the software architecture is in place and solid. I have about 6 months of episodic work into it and am really looking to push this forward.

In short, not dead yet.
-PM.
 
#33 ·
Re: About that 1/4 wave resonator I added ...

If you haven't already bought the woofer, you might want to google for "activesound auspuffanlage". That company makes a rugged, steel-encased woofer unit that is connected directly to the exhaust pipes and is used in several OEM Euro-market cars to tune the exhaust. It can be used to make an exhaust almost totally quiet, or to give a 4-cylinder a V8 sound, or a V12 sound, etc. There are some videos of the Euro vehicles (diesel VW's and Audi's) sounding pretty good with this thing.

So far as I could find, only Auspuffanlage makes the units right now, and in the USA, they only show up in the BMW i8 (since we don't get those diesel vehicles from Audi and VW). Fortunately, I found a unit from a wrecked i8, but they also seem to be available for about $500 brand new from the BMW parts stores. I haven't gotten very far with it yet, but it seems to be about a 4-Ohm impedance, so I'm hoping it will work with an off-the-shelf subwoofer amp. The i8 unit might be a bit small (it's only for a 3-cylinder, after all), but I suppose you could buy two of them.

Here's the actual unit I bought.
 
#35 ·
Re: So not done now ...

A couple of great posts! I'd love to get my hands on one of those BMW units. And Brian, did you get long or short -tube headers?

Thanks,
-PM.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top