jwbeck17

Just was thinking about this...has anyone added an aftermarket valved muffler on a 928?

I currently have an X-pipe, no cats, GT resonators and the stock muffler running. While overall that sounds good, I do miss when I had the rear-muffler-delete setup, however that was too loud for the neighborhood on early mornings!

Would love the best of both worlds where I could be reasonable in the neigborhood while less restricted on the highway at the touch of a button.

Anyone have any experience with this?

Tom. M

Check with Porken, he's done something similar using valves on the pipes (not muffler) hooked to vacuum.
Apparently worked really well.

Zirconocene

@Michael Benno has some video that I took with them on his car; I believe he made a post about it. If you can get past the maniacal laughter as he's doing some high rpm runs, you can hear how @PorKen stuff is working (hint: it's pretty great).

Cheers

Michael Benno

Adding a valved exhaust is something that @PorKen has been working on for a little bit. In our experience, many of the aftermarket exhaust mods leave the car a little loud or with the drone at cruising speeds. Between the two of use we have experience with about 15 different different aftermarket exhaust variants. Most have issues with being too loud at cruise (including RMB).

We looked into adding a valve to the rear muffler. However, if a rear muffler (OEM or aftermarket) is used, there isn't much room for a valve. @PorKen has been developing a valved exhaust near the cats, where there is more room. See below. The resting state of the valves is open with no vacuum (Full load or WOT). At full vacuum (idle and cruise), the valves will partially close to a preset amount (i.e., 50% closed). The return spring helps open them fast to prevent restriction under full load. These are vacuum-actuated and controlled by Ken's custom coding on the LH.




I have been running this mod on my GTS for a year or so, and it really helped tamp down noise under cruising, so it sounds much closer to stock sounds. My exhaust setup is X-pipe + Cat Delete + 2.5" stainless tubing, plus three Magnaflow mufflers. The rear muffler is very small and does a poor job of absorbing sound. The valves helped immensely.


This photo was taken when car was an automatic. It has since been converted to a manual 5-spd.


Here is a shot Ken's 1989 S4. This car came with an extremely loud 928MS 2.5" free-flowing system. You can see his valves between the x pipe and mid resonators

Michael Benno

Glen, I cant find any video from that day. Maybe we took the video on your phone? If you can't find it we will need to create another.

Zirconocene

@Michael Benno : I'm sure I still have it on my phone; I'll put it on a Google Drive folder and share it with you, so you can share as appropriate.

Cheers

Gary Knox

This type system was OE stock on two cars in my garage - MB SL55 AMG, and Aston DB9 Volante. When the vacuum drops, exhaust has a bypass through the mufflers. Each one goes from Casper the ghost (well nearly) to Valkyrie instantly as you hit the accelerator. Love that method of operation, and it looks like Porken's system is nearly there. The Aston can be made to always be in Valkyrie V12 mode by pulling a fuse in one of the electrical panels, but it is then 'out of character' to me (but with no vacuum at startup, the Aston always has about 1 1/2 seconds of 'DON"T FORGET I'M HERE' when it comes to life...Both cars were produced in the first decade of this century.

Gary

Michael Benno

Gary, the @PorKen system is already there and beyond. The first prototypes used a manifold vacuum to actuate the valves directly. This passive system worked pretty well, and the valves blindly followed the manifold vacuum. The valves partially close (quieter) under cruise and idle conditions (high vacuum). Conversely, the valves would open quickly (louder/less restricted) under high load (no manifold vacuum). This was a passive system and did not allow for additional logic.

Ken, being the mad scientist he is, evolved the solution so the vacuum inputs are now controlled by the LH outputs to optimize the valve opening/closing for specific scenarios. We need @PorKen to jump in here to explain what conditions it will optimize for, I cant remember.

grepin

Hi I have thought about this. Done by a fellow Aussie.

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jwbeck17

I'm really interested to see what @Porken has figured out! It looks like it simply bolts in to where the cats would be, then it would be the vacuum/wiring connections.

I do mis my RMB, but I do want stealth mode sometimes!

hacker-pschorr

My 79 has has a custom rear muffler since the late 80's that has an internal valve that either runs wide open or forces the exhaust through a muffler chamber. It fits in place of the factory pumpkin.

It's fun on track days with DB meters, close the valve when coming out of the corner with the meter. Also great in tunnels.

Packed full of "muffler material" it's amazing how quiet it is when closed. This is the only muffler on my 79 behind MSDS headers.

belgiumbarry

i found my C2 ( 540 Merlin ) with 3" side pipes way to loud for cruising and.... neighbors .... i welded "normaly closed" vac valves ( with electric switches ) at the end of the side pipes before the elbow tips . In front of them i made nozzles with oval tubing ( ground clearance) going to a X , glasspacks and a Porsche ( 997 ?? ) muffler. I just searched for one with 2 x in and 2x out 2.5". Of course here i could use the ex spare tire space. Now nice acceptable sound for cruising !
So i start always silent , once with engine vac i can open them and switch them electric to "open" or again closed by breaking the vac . I did have to put weaker springs in the vac pots as my engine vac wasn't enough . ( 11-12" at idle )

PorKen

I am using the S4-up LH controlled fuel vapor venting output to control a (996 flappy) solenoid valve. The valve is fed manifold vacuum and controls two normally-open exhaust valves on the X-pipe, with an external balancing spring to tune the internal valve pot springs. I wrote code to make rpm thresholds for how fast the electric valve is pulsed. At idle and up to 1800 rpm the exhaust valves are nearly closed with high manifold vacuum. At higher rpms or WOT the valve is opened more. With heavy throttle (or boost) the exhaust valves will open more because of reduced vacuum.


I need to make a new thread detailing all the steps making this supercharged S4 with X-pipe and 928MS 2.5" SS exhaust decently quiet at part throttle.

jwbeck17

This looks like a fantastic solution for the catless S4 driver such as myself. Not an off the shelf solution, so how does one evaluate the plusses and minuses of building/costs/installation of something like this?

Michael Benno

The main benefit is noise control. The valve definitively reduces the exhaust noise when idling and when cruising and reverts to more noise when under heavy load.

This benefit applies to those who have fitted a modified exhaust, and the end result is more noise at Idle and at Cruise. To my knowledge, there is not really any performance benefit. For those who have updated their exhausts to be free flowing (eg: Cat Delete, Larger pipes, Straight pass mufflers/resonators) there is a performance boost but often (not always) an increase in noise as well. So these valves can help bring the noise down when you want it.