Vacuum Operated Active Exhaust & VarioRam 3.6

[AlBackus36]

I'm writing this post to see if others have experience with the two subjects working in unison. It is my understanding that while in transit, and while open, the active exhaust vacuum cylinder that drives the valve is OPEN, meaning vacuum is venting to atmosphere. The VarioRam system is very sensitive to vacuum capacity and if you recall, the 993 came with the eggcrate vacuum canister. This canister is made up of ~11 3" balls for a total volume of about 155cuin of vacuum capacity. This setup is not messing around when it comes to available vacuum. The 993 also requires a start-up vacuum capability check that drives the two intake trumpets and the resonance flap. I have no idea what the computer thinks if they can't be commanded, or if it can tell they are not in the commanded position.

Does anyone have a vacuum controlled active exhaust on their VR intake 3.6? Have you struggled with cold-starting and available vacuum after sitting? I know that these systems also struggle on carbed engines or other setups where maintaining a mostly constant or readily available vacuum is critical.

I'm going to use this thread to troubleshoot my system as I've got some ideas on how to make it work. I'm currently leaning towards swapping the cylinders to 'normally closed' so that the valves stay closed at start-up and require a pressure to open them. I will then try driving them with an SAI pump that is triggered by a vacuum switch. When vacuum drops (throttle opened heavily), the vacuum switch will close, triggering the SAI pump to run. The valves take 4-5psi of pressure to open which I'm guessing the SAI pump can handle. It's all very complicated and part of me wants to just cut the valves off. The headers and valves are stainless, and I've never MIG'ed that, but figure I could get it to work if I can't get this sorted with my mad scientist attitude.

Open to input from the collective audience, otherwise sit back and watch me fumble over this lol.

[AlBackus36]

The stop gap that I've installed to mitigate this in the meantime is installing a check valve upstream of the valves that allows them to close, but not open.

What occurs is that after sitting the car is 'flat' in terms of vacuum.

You start the car and the valves are open. Loud start. Car runs rough as vacuum builds. Car slowly returns to running correctly once vacuum capability is restored. This can take up to 3 minutes of driving and usually is over once you have some time with the throttle closed and engine braking.

Once vacuum is built the car runs great and as expected. The check valve helps keep the valves closed so the active exhaust system is not currently effective. When the check valve is removed, the car runs like it has a vacuum leak. Raised idle and rich smell from tail pipe. The valves open under any amount of acceleration and there is noise and some power as expected.

[Duc Hunter]

On my 964 3.6 I "T'd" into the vacuum line that opens the intake valve, and ran that to my valve. It opens perfectly with the intake at ~4,500 RPM. I toyed with installing the MSD RPM triggered switch and solenoid, but it is still on the shelf as tapping it to my intake flap line worked great. I think I put an inline valve so that vacuum only flows one way out of the egg vacuum canisters for each line.

My valves are closed, and vacuum opens them. Thats the only way I could make it work.

[AlBackus36]

Duc, excellent.

You have normally closed valves that are opened with vacuum? Can you send me a link to what you have? I thought normally closed valves are intended for turbo cars and driven by pressure, not vacuum.

Would love to see your setup.

EDIT: Just realized you don't have a VR, but you do have the resonance flap still. The 964 came with the eggcrate too?

[Duc Hunter]

Originally Posted by AlBackus36

Duc, excellent.

You have normally closed valves that are opened with vacuum? Can you send me a link to what you have? I thought normally closed valves are intended for turbo cars and driven by pressure, not vacuum.

Would love to see your setup.

EDIT: Just realized you don't have a VR, but you do have the resonance flap still. The 964 came with the eggcrate too?

Not at home where I can dig up my pictures at the moment. Got my old valves at a local exhaust shop. Current valves are part of my Rothsport Racing headers and GT3 muffler setup. Rothsport asked me how I wanted my valves, and I said "apply vacuum, valves open."

The 964 has a vacuum reservoir, which mine was missing when I got it running, so the intake valve was not working. I added a single ball shaped reservoir to the system, like your egg crate, and it's worked for 10 years. I can even hear the intake flap move when teh key comes on. On a 964 it does a test open/close when the ignition comes on.

[AlBackus36]

I'll reach out to Rothsport and see what they say. Thanks again Duc.

EDIT: Duc, if you do get the gumption to take a picture. Can you note whether your valves are open at rest after sitting?

[AlBackus36]

Duc,

Have you actually filmed the valves to confirm they open with your check valve installed?

[AlBackus36]

Double post. Oops.

[Duc Hunter]

Getting pics of my valves is very hard because teh actuators are inside the bed right near the muffler, as you can see in these 2 pics.

And yes the exhaust flap move with the intake flap on ignition startup. NO I did not film it, I watched it happen when I had someone else cycle the ignition. So I am satisfied they work as advertised.

[Duc Hunter]

One more detail, Rothsport racing, does not sell the valves separate. I have their entire exhaust system, including their headers, their valves and connecting pipes, and a GT three muffler. You can actually find the required valves of a good quality on Amazon. That’s what I did for my old exhaust that I had a valve in.

[AlBackus36]

Thanks for the pic and confirming they operate as expected. The cylinders on yours look higher end than what's on mine, but concept must be same.

Here is a pic of my setup showing dump valve location:



With no check valve installed, valves open very quickly and noise is obviously very loud due to location and proximity to header primaries. With check valve installed, valves are open at start-up, close, and remain closed due to check valve. There is still extra noise from them. Video below shows that valves do not open with check valve in place. The check valve prevents the airflow from travelling the other direction, allowing the valve to cycle open/closed.

View post on imgur.com

Without the check valve installed, the valves open frequently, the car runs as though it has a vacuum leak (it does through the minor leaks in the valve's pneumatic cylinders x 2) and has a fast idle plus rich smell.

This thread is intended to document my path to getting these to work without the check valve as I'm convinced cars with the need for vacuum canisters cannot run this style exhaust. Maybe we can make me eat crow here.

As-is car runs like crap for first few minutes until driven a short while. Car does not pass the initial resonance flap cycling after it's sat for a few days. I'm convinced it is the active exhaust valves that are leaving my vacuum capacity at 0 when started like this.

My current plan is to completely isolate the valve demand from the engine's vacuum system to rule them out as a culprit.

I have so far:

1) Tested vacuum system with handyvac
2) Replaced all three VR actuators and two solenoids
3) Confirmed that I have sufficient vacuum capacity on a warm engine to run the initial start-up check 2.5 times. On the third go-round it's about half-way pulled in.
4) Ordered some replacement active exhaust valves that operate in a normally closed position and required boost or pressure to open them
5) Ordered a small air pump to push open the valves which will be triggered by the amount of available vacuum. Likewise this could be triggered with a throttle position switch or something else maybe?

Thanks for watching.

[RarlyL8]

We've done a bunch of the GT3 back box conversions using the default open valves. If the default is closed then the valve will be closed in the absence of vacuum. You want the valves open when the engine is under load so how would that work?
The valves need about 13"Hg to fully seat closed and are fully open at 5"Hg. ITB and carb setups require a vacuum manifold connecting all the throttle plates to achieve the vacuum requirements. The default open valves should snap shut the moment the engine turns over and begins making vacuum. I sometimes hear a quick bark if the engine starts instantly, without turning over more than a revolution or so. Electronic controls can be added to the valves that keep them closed or open when desired. This is what I suggest if your engine has computer controls requiring closed valves or you just want more control over the valve action.

[Duc Hunter]

Brain, when I apply vacuum to my valves they open, with no vacuum they close. I do NOT want them open below 3,500 as I don’t want it that loud. As I said above mine open when the DME opens the intake flapper on my 964 motor. As I am sure you know, on an 964 the DME triggers a vacuum solenoid to open the intake flapper valve and about 4,500RPM It also cycles this valve with key-on power as a test cycle. So that’s how it works on my 964 car. Should be very similar on the 993 engine, as I believe the intake flap system works in a similar manner.

Your method means at any RPM, if the driver goes on the gas moderately the valves just open. I had a setup like this on a previous exhaust and hated it. Unless your exhaust is very restrictive, you don't want it wide open in the low end, it just makes a lot of noise, drone and hurts torque. Watching a vacuum gauge while driving a driver will see that it doesn’t take a lot of pedal pressing to rapidly drop vacuum, especially down low in the RPM range. That’s why I chose the path I did. I wanted a quieter cruise and around town, a little more torque, wanted it loud when I gave it the beans, and I wanted it simple.

When I first got my car it had no vacuum reservoir, and no check valve. As a result the intake flap was not working. Once I installed those the system worked as designed. Later I tapped into the vacuum hose going from the solenoid to the intake flapper, and plumbed it to my exhaust valves. Everything works great. Everything works great on mine as is. No vacuum leak behavior like the OP is talking about either.

[RarlyL8]

Your method means at any RPM, if the driver goes on the gas moderately the valves just open.

That is not how our system was designed and not how it functions.
The valves open when the engine is under load. The valves do not fully open until 5Hg vacuum which means you control the valve action with your right foot. If you want the valves to stay shut while accelerating you can still accelerate very briskly without putting the engine under enough load to open the valves. The system also is not a dump pipe but rather it modulates the amount of back pressure going through the final muffler. We also have baffles available for the valves so the final sound can be tuned to your liking.
In Alex's system the valves are dump pipes but that is what he wanted. To keep them shut until XxxxRPM you add an electronic controller similar to a boost controller. But first and foremost your engine needs to produce enough vacuum for the valves to operate as designed.

Here is a video of our system installed on our Carrera. You can make the valves open by slapping the throttle, or keep them shut by being a little less aggressive.

[AlBackus36]

Hey Brian,

That's great to see it operate as expected on a 3.2 carrera. Those cars don't have vacuum canisters and don't have the same demand or the complicated system of a 964 or 993.

Any real life examples of these valves working on a VarioRam car?

Duc,

Do you ever run rough on start-up? Lack of power until vacuum has built? Anything like that?

[AlBackus36]

Here is the diagram for the planned setup. Still waiting for some parts to arrive.

[AlBackus36]

Alright so the plot is going to thicken a bit.

I have a neat John Bell tach that has an AFR gauge in it. I've got a spartan 3 mini controller that attaches to a wideband 02 sensor on the LH bank.

Out on my drives yesterday I noticed the following trends.

Idle: 14-14.5
Cruise: 14-15
WOT: 13-14

I'd love to hear if folks think these #s are lean. The internet says they're pretty normal for an N/A car.

These numbers did not change when I capped the active exhaust (preventing it from drawing on the motor) and pulling the valves closed manually with a handyvac.

When I shut the motor off, I get a woosh sound that emanates from the cone filter (sounds normal), but then I also get a more localized air pissing sound from the LH front of the engine compartment. It's not the FPR or the related plumbing.

I'll need to try a few tricks to see if I can find what I think is a massive vacuum leak. I'm going to try running the motor, shutting it off, and blowing some smoke at the area. I saw someone suggesting that the other day and thought that sounded like a good alternative to a party smoke machine.

Oh yeah, the new exhaust valves are here too. They are normally closed, vacuum to open, not pressure to open like I hoped/read else where. That's OK. I have a play for that too. The diagram doesn't change much except replace the SAI pump with a vacuum pump, that's really it.

More to come...

[AlBackus36]

Found the large vacuum leak!

It was the large vacuum line that runs up to the booster. Easy enough to pull a little slack and re-do the clamp so it doesn't budge.

I also confirmed that the car runs better cold when the vacuum system is not starting out depleted by the exhaust valves. I tested this by driving it around till warm with the exhaust valves isolated. Then, let the car sit for two days, then drove cold. Car performed closer to expected cold, still not perfect, but nothing like before. These varioram cars hardly get out of their own way when no vacuum capacity is present, or at least in my experience.

I'm now resolved in my decision to remove these active exhaust valves from the engine's vacuum system. They will be monitored through vacuum, but driven by their own isolated vacuum pump.

Logic will work like this.

Turn key on
No vacuum present in engine
Honeywell switch <10in-Hg; closed
Vacuum pump turns on
Valves open
Start car with open valves (loud start)
Vacuum builds
Honeywell switch >10in-Hg; opens
Vacuum pump turns off
Valves close
Drive normally with valves closed
Valves won't open unless engine vacuum dips below 10in-Hg.

I will be interested to see if the valves ever open with isolated systems and full capacity as the reservoirs will compensate when throttle is blipped.

More to come...

PS: I'm also learning the normally open valves make noise always. They may be closed, but noise is coming out of them. I tested this by trying different silencer configs. Whether the are allowed to open or not, cruise sounds different. I'll be also interested to see if the normally closed valves are quieter in cruise.

Thanks for reading.