I was tinkering-around the garage the other day, and thought the following might be of interest to members who have had similar thoughts, or just curious about the vacuum lines to the "S" standard and PSE exhausts.

The following Mod will eliminate the function of the Carrera S standard exhaust "flap" (well, at least one of them - see my note at the bottom of this post). The result is a sound that is deeper, a bit of drone, but definitely "on all the time" whether in standard, Sport, or Sport Plus modes.

This is a really simple DIY. Takes about as long as you need to get the rear of the car up off the ground, lay on the floor, and reach up to pull the vacuum line off. I spent about 10 minutes "exploring" and taking a few pics that follow.

STEP 1: Obtain some Vacuum hose end caps. You can pick-up some from your local auto supply shop (Pep Boys here in PA for me). I think these cost me $1.97 and come in variety of sizes. I happened to know that my stock vacuum hose was replaced recently by the dealer with a covered hose, so I needed a larger diameter cap opening than you might -- so getting a variety pack is the best way to go.



STEP 2: Raise the rear end. I pulled my car in the garage and up onto my Rhino Ramps - then put the E-brake on and chocked the front wheels so the car wasn't going to move on me! You don't need ramps, but they are safer than a floor jack alone.

Couple of pics on the ramps...





For reference, I have a 2014 C4S with standard, non-PSE exhaust. In this form, the center muffler is different than PSE and non-S cars, but does have the valve controls and vacuum lines. Performing this mod on a car with PSE should be identical, and may sound even better/throatier all the time.

I should also note that I have twice in the past year had one of my vacuum lines separate from the valve, so I was already familiar with the sound effect and so on. The big difference between those times and this mod is that you can eliminate the probably "Coolant System Fault" or similar warning that will occur.

Before moving-on to the next step I should state the obvious -- Let your car cool-down before you start putting your arms and hands into the areas round
the exhaust!! My car had been sitting for hours, and only started long enough to get on the ramps. Even still, I wore mechanics gloves and had on long-sleeve heavy shirt -- the space around the exhaust valve is tight and you will definitely come into contact with some hot surfaces! Please be careful! And while you're at it - wear some eye protection. You are looking straight-up into the bottom of a "dirty" area of the car and last thing you need is a bit of dust or worse falling into your eyes!

STEP 3: Locate the passenger-side exhaust valve. Approaching the car from the rear, get down flat-on-your-back on the floor behind the rear wheel and look up. Your vacuum line is likely clear in color, but could be other colors. I've seen white, blue and green. Currently, my vacuum line is clear with black insulating material - see pic below....



The hose just slips on the exhaust valve. So a gentle tug or two and the line should be free....

STEP 4: Pull off the vacuum hose from the exhaust valve. Here you can see I've pulled it off and it is just hanging...



STEP 5: Place a vacuum line end cap onto the vacuum hose end - use a cap that fits securely to the end of the hose. Too loose and it will fall off....



STEP 6: Tuck the "loose" vacuum line up and out of the way so that it doesn't come into contact with any heat sources, etc.



Final Pic:




That's it! You are done! You can start the car and immediately you will hear the difference. Drive it and in any mode it sounds better to me. I've driven for several days now like this, and have yet to see any warnings. The trick is to make sure that the vacuum line hose is capped, so the system can't tell that you've disconnected.

If, for any reason you want to replace, just reverse the procedures above. I did just that and it took 5 minutes.

NOTE: The steps above are for a single exhaust valve. Yes, I know there are two, and perhaps performing the same mod on the driver-side line will result in an even throatier sound. But I found that the other valve line is much harder to access from this position. So, if you are up to it you can tackle that one -- or, the alternative is to disconnect both lines at the "T" intersection. You can find this just a bit above the exhaust valve on the passenger side. Pull the feed line from the T connector, and cap that. But again, I found that in my garage, laying on the ground, reaching the T with my big hands was going to be problematic. So, I "settled" for only disconnecting the one
line....

I would love to hear from others if they've figured-out an easier way to
access the drivers-side valve, or the T connector mentioned above....

 

Could doing one side only create uneven exhaust back pressure?

 

interesting but curious to read more about this. Thanks

 

Interesting, and I gave this very question a cursory thought beforehand. But I don't have any exact way to measure this.... I've only had discussion with my tech at the dealership after the first two times where I had the very same vacuum line disconnect "itself" -- once while on a 2 hour drive to the shore house at high speed, and the other just simply starting-up one morning a month ago. In both cases I felt nothing in responsiveness or performance of the car, nor any other indication something had changed other than deeper sound and a coolant system warning message at the display. Acceleration across the range seemed consistent to me.

But again, I would have to measure the pressure to tell you for sure. Until then, I'll do some more testing. I may also pull the line at the "T" juncture, plug that -- it appears to be a single hose line coming from the COV solenoid to the "T" connector and then branch out to each valve. So I would expect to hear or feel some difference if there were any distinct changes in back pressure.

Am I the only one who gets excited by this stuff???

 

If the line can be capped without issue, why is it even there?

 

This should get some debate going, I am sure!

I am assuming you aren't asking about why the vacuum line exists.... As for why it can be "capped without issue" is because capping closes the loop. If you pull the line and don't cap, the loop is broken, and yes the car will throw a warning message. Cap the line, and the computer believes all is good, even though the valve or valves are no longer opening/closing. The valves control exhaust flow to the side mufflers - remove that from the equation and you simply have a single center muffler. The car doesn't monitor whether the valves are functioning or not as far as I can tell.

But hey- I am not an engine / exhaust expert -- there are plenty of those on this board who I am sure know more about this than I do!

 

I wonder if anyone has capped both sides or the "T" as you stated? Great pics! thanks you jawells1

 

Kind of made me think about the old "if a tree falls in the woods...." kind of question!!! Thanks Comp....

 

I'm still surprised that no one else has an opinion or information on this mod.

 

I don't even have the save valve and vacuum line as you. here is a pic of behind my rear passenger side wheel. Is this possible?

 

If you have the base 3.4L the mod is a non-starter, since you don't have the vacuum lines or valves - period.

 

There seems to be some confusion on how these work, let me help explain a bit.

Base Carrera 3.4's do not have the valves.

"S" Models have the valves that are operated for noise / sound only (not performance) and controlled by the engine management software and activated through a simple vacuum operation. In a 991 S, with or without PSE (doesn't matter), the sequence is this:

At Idle : The Valves are OPEN to make more noise
From off-idle to 3,400 rpm in every gear: The Valves are CLOSED for quiet
From 3,400 rpm to redline; The Valves are OPEN.

This feature is designed to give you quiet when on the phone in your car, or your lady is in there with you chatting away, or when you don't want your exhaust competing with your sound system. By capping off the vac lines, you eliminate the feature and they stay open all the time. Here's what the system looks like:

 

Excellent follow-up drcollie! Thank you.

 

thanks!!!! Back to the drawing board. LOL

 

Just to clarify before I actually do this.
I have PSE on my c4s, will it make it louder than it already is or will it just sound the same when it is in the loud position with it the button on or off.