Needsdecaf

So I am aware of the dearth of bad solenoids in the 991, effecting multiple systems. I suspect that one of the boogers in my HVAC system might be bad since when it's cold (Texas cold, we're talking 40's here) the car blows cold air for quite a while. And in the summer the AC is immediatley ice cold. But I digress.

So this afternoon I needed to "run a few errands" and get out of the house and enjoy the 991 by myself. I had the car in Sport, PSE on, and was regularly shifting at 7k RPM plus. Oh what a glorious noise! Since it was near 100 here, the top quickly went back up, and I was comparing the noise of the sound symposer top up and top down.

At my second stop, the guy at the register asked if I had driven up in the 911. I told him yes. He said his neighbor had a white one like it and that even at low speeds, "it just growls". It sure does, I said.

Get back in the car and drive to grab some beers for tonight's grilling and I notice something amiss. Cycled through PSE on and off, Sport, Sport Plus but nope, I can tell that while the exhaust is cycling open and closed, the sound symposer is remIning resolutely shut. How can I tell? A few months ago, I pulled up the cover behind the rear seats and plugged up the end of the tube with a towel and drove like that for a day.

So, I drove to my last stop and then home, about 10 miles, with the symposer not working. I could definitely hear the exhaust a lot more, as well as a lot more engine noise. Valvetrain, injectors, etc. It's far more mechanical sounding than when the symposer is active. And honestly, it reminded me of.....the .2.

I know I may be bringing on a legion of haters, but I'm not being a troll or trying to be controversial. I don't have a lot of .2 seat time (read two test drives), but honestly the level of engine and exhaust noise is, if I recall correctly, pretty similar. I would love to actually try a .1 with PSE and no symposer back to back with a .2. Anyone in Houston want to try?

It would make sense. The turbos naturally muffle the exhaust, but Porsche can open that up a bit. What they can't replicate is intake noise. Having owned (and currently own) turbo cars, some with modded intakes, I know that turbo intake noise is a lost of whooshing and hissing, versus an NA engine which has a honk / howl sound. This much I knew, but what I didn't realize is just how much of that intake sound in the 991 is from the symposer. It is, I would estimate, 60-70% of the howl that you hear with the PSE open. One other thing that was odd to note is that the symposer also pipes in a lot of the overrun pops and burbles as well. Those are quite muted with the symposer closed.

I wonder if you could do a manual override of the symposer valve. I know that with it closed, but PSE on, the car is quiet enough for family cruising. And I prefer it a lot more than with the exhaust valves closed when all you hear is engine noise below 3,500 RPM. Or even do a valve control that you could open partially, not just on or off. I'm no electrician / EE so I have no idea if that could be done easily.

Either way, time to get the car in for service!

Airandwater

The sound symposer is controlled by a different changeover valve than the PSE, so in theory you could control the two independently.

The way the sound symposer is turned on and off is with a butterfly valve between the airbag and the diaphragm. The valve is open when vacuum is applied and closed when it is not I believe. You would have to vary the amount of vacuum to vary the opening of the butterfly valve. Not easy. It's binary as is. SO you could install a switch to interrupt power to the changeover solenoid, but modulating it would be a lot harder. There is a version of the symposer developed for some manufacturer that uses an electric valve, so the opening can be varied. But I forget who that is. Might be the Cayenne GTS actually.

Needsdecaf

Does sound like it would require a new controller for the valve.

Airandwater

PS. It should say airBOX not airBAG in my post. That's autocorrect for you.