Nine1won

I did Fabspeed secondary cat bypass pipes and ECU tune. Amazing increase in power and sound (Fabspeed says another 100hp). Love it! Still will pass smog in CA with primary cats.

Dilberto

How does it pass CA visual inspection? The belly pan still needs to be removed, to "see" primary cats. Do you personally know a smog tech who will turn a blind eye to shiny T304 test pipes? I'm very close to mine.... but he told me he would not hesitate to fail me, if he saw that modification.

Nine1won

I was told by my mechanic at the Porsche dealer that they (secondary cats) are only there for sound. The primary cats are what pass smog. I guess if that is not the case, I can reinstall the secondary cats. I've kept them.

fortysixandtwo

I'm not saying they're needed to meet tail pipe emissions standards, but I highly doubt they are only for sound. Porsche (or any other manufacturer) would not use a catalytic converter for sound manipulation, when similar or better results can be had at 1/20th the cost.

peppapig

My car is a 2009 4.8 GTS with the standard switchable Sports exhaust. Recently I needed to replace the flexis. I found a local guy who would replace them with aftermarket flexis (shorter ones than OE) without having to remove the pipes from the manifold. That saved a lot of labour costs. I also purchased from eBay a set of used secondary decat pipes made by Hanksville Hot Rods and these were fitted at the same time.

Sounds great! With the exhaust in normal mode the sound is sporty but acceptably subdued. In Sport the sound is absolutely brilliant and exactly what I was hoping to achieve. It might, however, be a bit too much for some of our local trackdays.

The reason I am posting this is because there are some comments in this thread about extra power or not. Now, of course, the car sounds faster but as I have not had it dynoed I cannot say whether or not there is more power. What I can say is that these exhaust mods appear to have given a noticeable decrease in fuel consumption.

Fairly unscientific, but I always fill the tank and zero the trip meter, and I use the combination of the trip meter reading and the remaining tank range on the dash to keep me informed about the situation. Since the exhaust changes, that total has been at least 60 miles more than before. The effect seems to be greater in Sport mode than in normal mode. It is not just the odd tankfill when this happens, it is with every tankfill. I have now done just over 3500 miles with the new system.

Remember, we are paying more than $8.50 per gallon for premium fuel, so any improvement is usefull.

The only downside to the mods is the really weird noise that the exhaust now makes on cold starts during the cold start cycle. Only for about 3 -5 seconds so not a big deal!

peppapig

vtgt

medtech

To the OP...bypassing the secondary cats is a good solution and you can DIY. Personally I would do one, or the other (meaning muffler), but not necessarily both. I wasted a lot of time and money a few years ago by originally bypassing the secondary cats which was fine, then I stubbed onto a used Cargraphic exhaust and had that installed. Let's just say that the resulting combination was SOOO loud that I couldn't drive through a parking garage without setting off multiple alarms. It was fun for a few months, but it was definitely too much. So, long story short, the cheapest and easiest is to bypass the secondary cats which you should be pretty happy with (based on my experience on my 2006 C S.

I share your sentiments about FS. Personally don't like the sound of their mufflers and have had bad customer service many years ago.

This is known on the forum as a "Fister" mod. I've never seen or heard it on a Cayenne, but it was perfect on my 996.

Depending on the year of your car you should have 2 sets of cats. The main set I would leave alone, but the secondary set is fair game. I don't think they would affect a smog check and a tech won't notice because the car still has cats.

nrddct

Ive noticed that too. Win win situation

Dilberto

vtgt

Petza914

I have the HHR Intake, IPD plenum, Fabspeed Secondary cat bypass pipes, a cargraphic touring muffler (this is the quieter one), FVD intercoolers, Evoms Diverter Valves, and a Fabspeed Stage 2 Tune and couldn't be happier. A nice subued growl most of the time, properly vocal under hard acceleration, but very quiet on the highway just cruising along. For my tastes, it's perfect.
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gimp2x

i have a set of pipes that replace the primary cats on the 955 cayenne for sale on here, they really pickup the turbo response, and make the car very throttle sensitive, which is great for having fun, not so great for passenger comfort

dpatel710

I'm not sure if it can be done the same for the 957, but the internal muffler bypass is a great way to add extra noise for cheap from the outside. I never noticed it while in the drivers seat, but when someone pulled away in the cayenne, it had a nice burble to it.

I recently did the cat bypass, and as others have said it is a lot more raspy/angry sounding. It is fun for now but I will probably go back and pull the internal muffler bypass in a few months to quiet it up.

As for anyone who searches later on, I'd give the circuit werks cat bypass an overall D grade. The bends match up correctly but proper fitment required welding gaps on the sleeve clamps due to pipe diameter mismatch and extra hangers to reduce rattling.

Twintipin13

I love the way my 08 Cayenne Turbo sounds at cold start, but from what I can tell in the cabin its the best sounding/most agressive note the vehicle puts out. In sport mode there is not much difference in exhaust sound from the normal mode. I wish the sport mode made it sound like it does during a cold start. Also the previous owners removed the cats. not sure if that changes how the vehicle sounds or affects the 'sport mode' sound?

Petza914

Unless a PO changed the muffler to something aftermarket with a vacuum valve, only the GTS has a valves exhaust that opens up for more sound and flow in sport mode, not the Turbos or the Turbo Ss.

That sound on cold start comes from an enriched fuel mixture used to warm the cats faster for emissions purposes, which is ironic since you no longer have the cats.