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BTW, if you haven't already, you might look at modifying or blocking the car's sound symposer port, for it has a significant effect on the engine sound as it is experienced in the cabin.
Your link goes to the Evolution Line (titanium) which shows an increase in torque.
The Sharkwerks verbage means nothing....its talking about sound.
You said "valves staying closed provide more low end torque. And when they stay open the car loses low end torque". Is there an independent shop, that doesn't sell exhaust systems, that shows specifically your claim?
I'm not trying to be argumentative, but I've heard this repeated so many times, yet I haven't read anything to prove it. If your correct, so be it...I'll have learned something. What'ya got?
All SW did was take their 997 bypass, throw it on the 991, and decided it sounded good knowing there isn't much else to be gained.
I heard it too over and over too. I don't believe it's true. As you know, I've actually tested it and have tried several different exhausts.
Porsche manual states torque increase with sport butten on above 3 K. They spend millions in development so I would guess they know something. It appears the valves help to increase torque range and drivability. I think this is why so many shops are only changing center exhaust to improve sound.
Note Dyno charts do show a drop in torque below 3K. Check Akrapovic dyno charts for development of their system and you will see what I am talking about.
Porsche gets extra torque boost below 3K by running extra back pressure via the length of exhaust path. I have yet to get an answer from Fabspeed regarding the torque of their bypass using extra length of rear can vs side cans.
The car does make extra toque in the 3 to 4K according to Porsche with valves open via the sport switch.
If cruising below 60 in 5th gear car has good torque in 7th gear with RPM about 2K. The loss with BBI is certainly there.
Not sure who you have spoken to here, but I was unaware of your questions. We have not dynoed JUST the side muffler bypass pipes with valves. Firstly, we didn't have a valved set made in the time that our production car was here, only valveless. Second, we didn't see a need to dyno them. It might be interesting to know now in retrospect since we have the valves. I know you are curious what differences there are between side muffler bypass pipes with and without valves at various RPM ranges, however I do not think it will be worth the hassle to observe such details at this point. We are really splitting hairs here IMO.
For me, I prefer the valved bypass pipes for the change in sound and all of my customers certainly are pleased with the sound and performance!
Porsche manual states torque increase with sport butten on above 3 K. They spend millions in development so I would guess they know something. It appears the valves help to increase torque range and drivability. I think this is why so many shops are only changing center exhaust to improve sound.
I can see why they say this but it still doesn't conclude if the valves open all time hurts low end torque.
I have mine forced open now but have thought of going back to stock cause I hate having a button not functional along with possible lost torque.
I personally think the valves are there for sound regulations only but they are tossing it out as a performance thing.
In December 2011, the European Commission proposed a new Regulation (COM(2011) 856) to replace the Vehicle Noise Directive and to lower traffic noise levels by around 25%.
The proposal is for noise limits to be lowered within two years by 1 dB for trucks and 2 dB for cars, vans and buses; and by an additional 2 dB for all vehicles, three years later.
The purpose of this system according to the motorcycle manufacturers’ marketing departments is to create back-pressure at lower RPM’s to increase torque. Unfortunately, this probably isn’t the real reason; the true purpose of the exup valves is to meet noise and emissions regulations. The exhaust valves are partially closed at idle and low rpm to reduce noise, and closed again at the upper RPMs to meet peak noise and emissions regulations. The proof of this has been shown on the dyno where removing the valves and retuning the engine creates a flatter better torque curve.
This is cracking me up. I keep typing things up and deleting them as to not offend.
"But, but, but...the manual says..."
PSE ON Valves Connected in BLUE
PSE ON Valves Disconnected in RED
Both runs were in 3rd gear at Moderate Throttle. I guess one could argue that we didn't press the accelerator exactly the same, but that shouldn't matter since the car is making virtually the exact same amount of torque valved and valveless.
You could also argue that the plot doesn't start until around 2,300RPMs. Well, let's keep this simple. The car idles around 1,000RPMs, so that leaves us with a pretty tight window to lose a bunch of power. Oh, and the RED line is above the BLUE at 2,300, so the arguement of lost torque and disconnected valves isn't working for me.
So now you could argue that the valves are operating the same with the PSE ON whether or not the valves are disconnected. Which isn't true as you can audibly hear the valves opening and closing with the PSE button ON, but for fun lets turn it off so we can't argue that the valves are functioning to save us all of this torque.
PSE OFF Valves Connected in BLUE
PSE OFF Valves Disconnected in RED
Hmm... I guess you could aruge that the RED line starts at 2,500 RPMs.
Thie biggest source of back pressure is the cats. Anything after that is six of one and half dozen of the other IMO.
I think we are probably getting some backpressure and low-end torque optimization from the side mufflers and their goofy design. So when you delete them you may loose some low end torque, but gain midrange and upper end hp/torque.
I bet this car is measurably faster than stock with it more linear torque curve, additional power, and 40lbs. lighter despite the slight amount of lost torque. Although I didn't dyno my side muffler delete, I didn't detect any any difference. There may be some, but it's not significant.
I don't think the comparison with the Cup car is relevant here. Cup cars spend most of their time in the higher RPM range,so less back pressure is beneficial.
The GT3 on the other hand spends quite a bit of time in the lower range where back pressure is beneficial to the lower end torque.
Just my 2 c...
I would agree with Evan that it is probably not worth testing as loss in torque is low; however I am anel and been looking at this with interest.
The car is fine through town with valves open & on the high way at the 2 K figure but my testing does show a difference. Personal testing has been done on a given grade using time and distance in 7 th gear at 2 K accelerating, valve on and off & in car power meter.
Your link goes to the Evolution Line (titanium) which shows an increase in torque.
The Sharkwerks verbage means nothing....its talking about sound.
You said "valves staying closed provide more low end torque. And when they stay open the car loses low end torque". Is there an independent shop, that doesn't sell exhaust systems, that shows specifically your claim?
I'm not trying to be argumentative, but I've heard this repeated so many times, yet I haven't read anything to prove it. If your correct, so be it...I'll have learned something. What'ya got..
Akrapovic makes both sestems with valves & without & with & without side mufler. Their own graphs show a difference.
I may add : from driving the car and reading quite a bit about it-I am fairly certain to say that the Porsche exhaust system is extremely well designed and it is very hard to improve! The only thing you can do is what Sharkwerks and others have done : and that's to eliminate the 3rd muffler to get more sound. Other than that,it's just a waste of time and money IMO.
06-11-2015, 10:01 PM
