DIY Video: Disconnecting Exhaust Valves
12-15-2014, 05:16 AM
#31
Three Wheelin'
Not saying my butt dyno is better than yours but FWIW, I felt that torque in the low rev range was diminished when I did this mod and posted a DIY (not as nicely done as yours) about it a couple of months ago. I ended up switching things back. BTW, I used wire instead of plastic to tie things off because of the heat involved in that area. The PSE is fairly sophisticated and IMO simply blocking the vacuum source negates some of the other features built into the system. For anyone who is interested, this is what the Porsche tech intro docs have to say about it. Regardless, well done vid and beautiful car! Switchable exhaust flaps Like its predecessor, the 911 GT3 (991) has a function for increasing torque in the middle rpm range. This function is not activated by pressing a SPORT button as was the case for the previous model, but instead using the button with the twin tailpipe symbol (1) in the center console. When this button is pressed, the torque is increased in the middle rpm range. The exhaust backpressure in the variable exhaust system is additionally reduced and the gas cycle is improved, resulting in a noticeable boost in torque in the rpm range between approximately. 3,000 and 4,000 rpm. The torque levels are increased by between approximately 22 and 26 ft. lb. (30 and 35 Nm). The maximum torque of 325 ft. lb. (440 Nm) at 6,250 rpm remains unchanged. The switching point of the exhaust flaps depends on the load and engine speed. As on the 997 GT3 II, the switching point from closed to open at full throttle is 3,200 rpm (exhaust flap button (1) pressed) and 4,000 rpm (exhaust flap button (1) not pressed).
12-15-2014, 08:50 AM
#32
Here is what I'm going to do. I'm going to drive around this week and see if this is how I want the car to sound. I went out to pick up some oil to do my first oil change. I think the car actually drones much less with the Sharkwerks bypass.
If I decide this to keep lines disconnected, I'm going to get a dyno done to eliminate all of this uncertainty. I'll do a back-to-back disconnect/connected.
My question is, don't I need a AWD dyno? I had read somewhere that 911s need to have the front wheels rolling. Is this correct? What gear should I use? Where is the coil pack, and to what color wire do I need to clamp the dyno sensor?
If I decide this to keep lines disconnected, I'm going to get a dyno done to eliminate all of this uncertainty. I'll do a back-to-back disconnect/connected.
My question is, don't I need a AWD dyno? I had read somewhere that 911s need to have the front wheels rolling. Is this correct? What gear should I use? Where is the coil pack, and to what color wire do I need to clamp the dyno sensor?
12-15-2014, 08:51 AM
#33
Burning Brakes
Call Champion or Brumos in FL, I am sure one of them could answer the dyno questions.
12-15-2014, 09:12 AM
#34
Three Wheelin'
Here is what I'm going to do. I'm going to drive around this week and see if this is how I want the car to sound. I went out to pick up some oil to do my first oil change. I think the car actually drones much less with the Sharkwerks bypass.
If I decide this to keep lines disconnected, I'm going to get a dyno done to eliminate all of this uncertainty. I'll do a back-to-back disconnect/connected.
If I decide this to keep lines disconnected, I'm going to get a dyno done to eliminate all of this uncertainty. I'll do a back-to-back disconnect/connected.
12-15-2014, 10:49 AM
#35
Alright everyone. I'm taking one for the team. I just made an appointment at Titan Motorsports in Orlando to do some testing. I'll post Dyno plots and video. Titan has an AWD DynoJet. This is going to be fun.
12-15-2014, 10:57 AM
#36
Three Wheelin'
12-15-2014, 11:39 AM
#37
Not saying my butt dyno is better than yours but FWIW, I felt that torque in the low rev range was diminished when I did this mod and posted a DIY (not as nicely done as yours) about it a couple of months ago. I ended up switching things back. BTW, I used wire instead of plastic to tie things off because of the heat involved in that area.
The PSE is fairly sophisticated and IMO simply blocking the vacuum source negates some of the other features built into the system. For anyone who is interested, this is what the Porsche tech intro docs have to say about it. Regardless, well done vid and beautiful car!
Switchable exhaust flaps
Like its predecessor, the 911 GT3 (991) has a function for increasing torque in the
middle rpm range. This function is not activated by pressing a SPORT button as was
the case for the previous model, but instead using the button with the twin tailpipe
symbol (1) in the center console. When this button is pressed, the torque is
increased in the middle rpm range. The exhaust backpressure in the variable
exhaust system is additionally reduced and the gas cycle is improved, resulting in a
noticeable boost in torque in the rpm range between approximately. 3,000 and
4,000 rpm. The torque levels are increased by between approximately 22 and 26 ft.
lb. (30 and 35 Nm). The maximum torque of 325 ft. lb. (440 Nm) at 6,250 rpm
remains unchanged.
The switching point of the exhaust flaps depends on the load and engine speed. As
on the 997 GT3 II, the switching point from closed to open at full throttle is 3,200
rpm (exhaust flap button (1) pressed) and 4,000 rpm (exhaust flap button (1) not
pressed).
The PSE is fairly sophisticated and IMO simply blocking the vacuum source negates some of the other features built into the system. For anyone who is interested, this is what the Porsche tech intro docs have to say about it. Regardless, well done vid and beautiful car!
Switchable exhaust flaps
Like its predecessor, the 911 GT3 (991) has a function for increasing torque in the
middle rpm range. This function is not activated by pressing a SPORT button as was
the case for the previous model, but instead using the button with the twin tailpipe
symbol (1) in the center console. When this button is pressed, the torque is
increased in the middle rpm range. The exhaust backpressure in the variable
exhaust system is additionally reduced and the gas cycle is improved, resulting in a
noticeable boost in torque in the rpm range between approximately. 3,000 and
4,000 rpm. The torque levels are increased by between approximately 22 and 26 ft.
lb. (30 and 35 Nm). The maximum torque of 325 ft. lb. (440 Nm) at 6,250 rpm
remains unchanged.
The switching point of the exhaust flaps depends on the load and engine speed. As
on the 997 GT3 II, the switching point from closed to open at full throttle is 3,200
rpm (exhaust flap button (1) pressed) and 4,000 rpm (exhaust flap button (1) not
pressed).
12-15-2014, 11:50 AM
#38
Instructor
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Way to take one for the team!! Much appreciated, can't wait to see the results.
12-15-2014, 11:55 AM
#39
I'm going to actually find out rather than just guessing. Friday morning is my appointment. I really need to stop jerking around on car forums and get some work done.
12-15-2014, 12:02 PM
#40
12-15-2014, 03:27 PM
#41
Race Director
Mike, maybe I'm reading this wrong but the way I interpret this post is as follows:
Below 4,000 rpm the torque curve is flatter on the graph (provided by Porsche on GT3 launch) then it spikes up after 4,000. As it is suggesting in the literature from Porsche, back pressure is reduced at 4,000 rpm when the valves open, thus giving more torque. Generally, as far as I'm aware, when there is less back pressure in the exhaust (more flow) the engine puts out more torque, at lower rpm. The only time the engine needs some back pressure is at the higher rpms to keep up that compression. So maybe having the exhaust open all the time at lower rpm would provide better torque between 1,000 - 4,000? Obviously I would have to try it in person to see the difference.
Below 4,000 rpm the torque curve is flatter on the graph (provided by Porsche on GT3 launch) then it spikes up after 4,000. As it is suggesting in the literature from Porsche, back pressure is reduced at 4,000 rpm when the valves open, thus giving more torque. Generally, as far as I'm aware, when there is less back pressure in the exhaust (more flow) the engine puts out more torque, at lower rpm. The only time the engine needs some back pressure is at the higher rpms to keep up that compression. So maybe having the exhaust open all the time at lower rpm would provide better torque between 1,000 - 4,000? Obviously I would have to try it in person to see the difference.
The quote from porsche is very useful thanks Mike. It basically says the button opens the valves giving more flow, hence less back pressure and more torque. Doesn't say anything about the valves being shut at low RPM to increase torque. So my question is: is your butt dyno the only evidence we have that this happens? Anyone else with this mod noticed it?
The Porsche info says that the switching points at full throttle occur at 3200 and 4000 rpm respectively, depending on whether the button is pushed or not. But the critical part of the info, IMO, is where it says that "the switching point of the exhaust flaps depends on the load and engine speed". My interpretation of this is that the valves are modulated by the ECU for best torque at part throttle, which is how most of us drive most of the time. I think the description indicates that the PSE control system is engineered to be more than just an on off switch at a specific RPM.
I wanted the mod to work. I planned out what I was going to do, bought parts, and took the trouble to post a DIY thread on the assumption that it was a no-brainer useful idea. But when I did the mod, not only did I not care for the blatt of the exhaust at low speeds, more importantly I felt throttle response was more mushy at low RPM. I undid the mod the next day, and when I read the tech info my decision was reinforced.
To answer the question, I have no empirical proof other than my own butt dyno. But it's my butt in my car so I've got to go with it.
It will be interesting to see what Money comes up with if he dyno's his car. I hope that the dyno run can reveal power output at more than just full throttle. If it can't quantify part throttle responsiveness and performance I'm not sure if it will really put this issue to bed. My belief is that the engineers who designed the PSE system had more in mind than coming up with a way to open and close valves with a little vacuum.I'm not trying to dissuade anyone from doing the mod. Since I had encouraged people to do this initially I felt obligated to share my rationale when I changed my mind. But by all means, draw your own conclusions.
Last edited by Mike in CA; 12-15-2014 at 03:45 PM.
12-15-2014, 03:47 PM
#42
Burning Brakes
Money, will you be showing the dyno live
Also, will you keep the SW bypass on to see if there is any power drop?
Also, will you keep the SW bypass on to see if there is any power drop?
12-15-2014, 03:53 PM
#43
Nordschleife Master
As far as I can tell,engines are nothing but air pumps. If you let them breath better(the exhaust gases have a less restrictive path to exit),in order to make more power,more air needs to enter and more fuel(which I believe it's not happening : 1)Because not much more air it's coming in at lower RPMs
2)There's no different fuel mapping when PSE On
3)The O2s are in Closed Loop at lower RPMs and the PCM is using their readings. Higher RPMs and the O2s go in Open Loop,the PCM is not using their readings,lets extra fuel going in,obviously extra air coming in,so it's beneficial to the engine to breath better)
Conclusion from the above^^^ : you lose TQ at lower RPMs but I want to see the Dyno.
2)There's no different fuel mapping when PSE On
3)The O2s are in Closed Loop at lower RPMs and the PCM is using their readings. Higher RPMs and the O2s go in Open Loop,the PCM is not using their readings,lets extra fuel going in,obviously extra air coming in,so it's beneficial to the engine to breath better)
Conclusion from the above^^^ : you lose TQ at lower RPMs but I want to see the Dyno.
12-15-2014, 04:11 PM
#44
Three Wheelin'
Thats what I am talking about!!!!! I always wondered why Car magazines didn't work with a local shop to dyno the high performance cars. Money Magazine will get it done.
12-15-2014, 04:27 PM
#45
Nordschleife Master
I can say one car that did not benefit from less Back pressure was the 996.2-3. I had a europipe 100 cell cat exhaust. The lack of BP caused the RMS to weep a bit of oil. First time I had it replaced. IT leaked again within a week after replacement. Eventually Porsche said that due to the way the seal is implemented, it needed the additional BP to keep the frog's *** sealed.