John@Fabspeed

You just need a programable valve controller that's set to open at a certain RPM. Perfect.

Sloopy

I have been watching from afar looking for the best answer to the sound question. Porsche has done an excellent job as usual so improving their system would be minimal.

Regarding valve operation; I'm not sure what every one is hearing. Valves are closed with vacuum and pushing the sport button appears to open them so if one wants to eliminate that part just push the sport button and be done with it.

The biggest difference in sound comes from the change in the induction system and cams at 4K so regardless of what you do with the exhaust this will still exist. Any manipulating to try and change this would alter how the engine performs and degrade the car.

If losing weight is the issue then bypass like BBI or Fabspeed would be a good alternative, but since once valves are open most exhaust passes though the lowest restricted area of the rear muffler there should be minimum changing of exhaust note vs just having valves open.

This leave us with the issue of sound. Once valves are open most of the exhaust passes through the rear muffler so if you wish to change sound, changing the rear muffler is the best and least expensive alternative. Any rear bypass will allow mostly unrestricted exhaust out the back of the car and the greatest (loudest) sound. This leaves the valves to operate as normal so in town and low RPM torque remains the way Porsche designed it.

From my research I feel the best option at this point, short of changing headers and cats, will be to just change the rear can to Shark Werks or GMG. I feel the GMG is a my choice at this point as I feel the larger pipes will change the tone as well as the sound level.

Sloopy

Valves are mechanical and operate fairly slowly compared to transmission so if you keep constant throttle, I would doubt you could ever catch the valves closing.

Money2536

That sound great, but doesn't exist for the OEM valves. iPE has an option but appears to lose tons of power.

Money2536

Porsche has done a good job other than including massive mufflers that weigh a ton and including valves that operate to simply control the amount of sound coming out of the car to adhere to regulations.

What do you mean what is everyone hearing? Pushing the Sport button doesn't open the valves. It simply changes when and how much throttle input is necessary for them to open. The change in sound you are hearing isn't a change in anything other than the valves opening. And no, changing an exhaust doesn't necessarily degrade performance or operation.

The exhaust note changes substantially when the side mufflers are deleted. It is much different than simply having the valves forced open with the factory side mufflers. Some exhaust gases still pass through the side mufflers even with the valves open.

Money2536

Nope. Do you have a 991 GT3? What does the transmission have to do with the valves on the exhaust?

Sloopy

You sated valves close during shift unless I misread. Valve do have effect on torque at low RPM.

Money2536

Valves close again when upshifting unless the upshift results in a starting RPM of 3,700ish or greater on the next gear.

Finlander

Do you have any links to information that proves this theory? You've said this more than once but I haven't seen you provide a single thing that validates your claim…unless I missed it?

Money2536

http://az79640.vo.msecnd.net/akrapov...8916e46600.pdf

Akra's dyno chart with their cup exhaust that deletes the valves and side mufflers shows a loss in low end, but it's not what I experienced. Now my dyno plots start at 2,800 RPM. Clearly the car makes more power with the side mufflers and center bypass with the valves forced open.





All I know is that Lodi and I were nursing the our cars at part throttle off the line at the 1/2 mile event. His was stock and mine had valves forced open. We ended up with-in 8/10s of a MPH difference in 1/2 mile.

Sloopy

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.

Sloopy

I wonder why exhaust sound at idle changes so much when the sport button is pushed???

Sloopy

https://www.akrapovic.com/#!/car/pro...60&yearId=3864

From Shark Works web site...
"Although we do not guarantee or make any crude horse power claims (let’s face it Porsche did a wonderful job already on this one) we can assure you that you have not likely heard a GT3 sound like this before. By retaining and re-using the stock side mufflers and valves you are also able to continue to use the factory "sport button" valve feature to open/close and send the exhaust gases through the sides for a similar to stock sound when you want to cruise and be akin to stock or then bypass the sides for a more exotic sound."

Finlander

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?

GraphiteGrey

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