PorscheACC

Yes, that makes me think that the exhaust flaps are closing at the end..

I wish I have the complete Cayenne S service manual. I had it fir my Mercedes since I used to fix the msny issues whenever I could.

Those manuals should describe the exhaust flaps and electrical/mechanical actuators.

Anybody has the service manuals? Maybe it us a quick mod for the fun of it.

Mike Murphy

I’m going to keep disagreeing with those saying the cold start is a richer mixture. I think it’s leaner, along with the ECU setting the camshaft timing, producing more overlap so that more air enters the engine and overlaps from the intake to exhaust to allow air to heat up the cats faster. The ECU also adjusts timing and opens the throttle more to make the engine act as a more efficient air pump (but less mechanical efficiency) - again to get more air through to the cats.

Richer fuel mixtures used to be common for carbureted engines because too much of the fuel would pool or liquify (only a portion would atomize) and not enough would get burned. A modern engine doesn’t have this problem, and instead, pollution is extremely high until the engine heats up properly (primarily the cats). So the best way to heat these components is a simulated load (a better load would be to drive off immediately and not idle the engine for any length of time) by opening up the throttle and making the engine less efficient. The lean mixture burns hotter than stoichiometric, and many cars would always run lean in an ECO mode scenario if it weren’t for the high temp downside of burned valves and such.

Quadcammer

unless the newest models are different, secondary air injection was used to pump air into the exhaust to heat up the cats faster. richer fuel mixtures are not used only to avoid pooling, but rather because cold engines are hideously inefficient and need more fuel to start and run smoothly. With direct injection, this may be a bit less prevalent, but its still inherent in IC engines.

PorscheACC

It's a richer mixture, as explained below..
--------------https://enginebasics.com/EFI%20Tuning/Start%20Tuning.html

Start and Warmup Programming

Background

Information Gasoline does not vapourize as easily at cold temperatures as it does at warmer temperatures. When the metal parts of an engine are cold and fuel hits them, the fuel tends to condense rather than vapourize. As fuel and air need to be in the proper proportions to combust properly, this fuel puddling problem leads to lean and rich regions in the mixture which are difficult to ignite. Generally, the mixture is extremely lean by the time it reaches the combustion chamber because much of the fuel has condensed and puddled in the intake manifold and ports, not reaching the chamber. Because of this phenomena, we have to increase the amount of fuel injected to ensure that enough fuel reaches the chambers to bring the mixture into its ignitable range.

PorscheACC

Well, after looking at some Audi forums some of them are able to open the exhaust flaps using an OBDII trick..

They can feel the exhaust flaps open or close with a stick.. If they open the flaps with the stick, they get the deep exhaust sound.

Not all of them were successful using the obdii trick to leave the exhaust flaps open.

I wonder if the 2019 Porsche Cayenne S which has an Audi twin turbo engine can work in a similar way..

https://www.audizine.com/forum/showt...aps-and-OBD-11

DDDl

Hello.I am
new here. anything new about it? did you find out how is it possible?

Ericson38

I know in the old days retarded ignition timing made an engine run warmer (one of the 1st things to check when overheating continually...plus down on power). It drastically deepened the exhaust note of the 1970 428 CJ Mustang I had. Advancing it made the engine speed up and the exhaust get quieter.

I think the ignition on the Cayenne engine is initially retarded for quicker starts and less cranking load on the starter, and this also heats up the cats faster. Retarded means the ignition happens after TDC, and the flame is most likely still present when the exhaust valve opens, depending on how many degrees they retard it.

Schnave

Yes, retarded ignition timing is just one of the many things used to light off the cats during cold start. One of the things NOT happening is opening the exhaust flaps. In fact, the sport exhaust is actually DISABLED during cold start. What? Then why is it louder?

Engineers use a multitude of techniques to heat up your catalytic converters as fast as possible. Until they are up to temperature (called light-off) emissions levels are off the charts.

Your turbos are huge thermal heat sinks. They also muffle the exhaust sound. A typical turbo will decrease the exhaust gas temperature 450°F between inlet and outlet during cold start. That’s bad for cat light-off.

During cold start, the waste-gates open and bypass the turbos to send hot exhaust straight into the cats to heat them faster. You get the added benefit of that raw, unmuffled V-8 rumble.

Lots of other things also going on. All of them designed to increase to exhaust gas temperature and speed the cat light-off. Many of them also affect the exhaust note.

• Close the sport exhaust valves to increase back pressure
• Enriched fuel mixture
• Fuel injection timing
• Delayed ignition timing
• Valve timing

https://dspace.mit.edu/handle/1721.1/81693
https://dspace.mit.edu/handle/1721.1/102387

Don’t believe the PSE is disabled during cold start? Watch my video of a cold start on my PSE equipped Cayenne. I placed strings on the pipes so you can see the airflow. PSE valve controls exhaust through the outer pipes. Notice the outer pipe strings are still during the cold start and begin to move immediately after the cold start process terminates.

Ericson38

I was referring to the two exhaust valves in the head, not the sport exhaust pipe valves, just to be clear in my comment. Ignition timing, if late enough, will result in a lot of heat and sound through the exhaust valves in the head.....

Schnave

Agree. Have edited my post from exhaust valves to exhaust flaps to clarify. I was addressing OP’s contention that the deep exhaust sound came from open exhaust flaps during cold start.

justabout

BINGO. Not sure if possible but the exhaust valve timing may be adjusted as well, opening early.

Mike Murphy

I suspect a lot of this cold start noise is also coming from the intake side. One downside of running late ignition is that efficiency goes way down, so a lot more air is required to keep the engine running.

21MacanGTS

Schnave nailed it. For a few seconds we have a n/a engine with little muffling. Illustrates how much turbos impact exhaust sound.

Needsdecaf

It's amazing what adjustments to mixture and timing can do.

The first few times I drove a 997 Turbo, I was CONVINCED that there had to be some sort of PSE system. When you put the car in Sport or Sport Plus, the engine note immediately gets noticeably deeper and louder. It's evident throughout the rev range, to the point where it can get a bit drone-y on the highway.

But the 997 Turbo has no PSE system at all. It's all down to the adjustments of timing, wastegate, VTG turbos, etc. It's pretty dramatic.