ONEOFEW

Fellow Rennlisters, I'm new to the 991 gen, wondering if there is a way to defeate the exhaust bypass function?
With the 997 gen electronic or vacuum line mods seem to do the trick, even in the Ferrari world it's very simple procedure.
Any way to have the valves permanently open?

Jimmy-D

Yes- The Porsche Dealer did this for me on Friday when put on a new rear bypass on my .2.. Right under rear of the car you have this hose on each side going in to this cylinder thing which you can see on one knee. He disconnected them and then used these plastic ties to secure them out of way. He then used screws to plug the holes. Best upgrade by far; so far. No more annoying transitions around 3800 rpms.

0to60

How hard is it to push a button to activate/deactivate the exhaust valve ? It's nice to have the option to keep car quiet when coming home late at night. Again it's a push of a button people.

ONEOFEW

NVRANUF

Pushing a button does not fix the issue with by-pass pipes.
In Sport the valves are open at idle (loud!) then they close when in gear and rolling off, then at 3800 RPM they open again. The opening-closing transitions with a by-pass pipe becomes VERY annoying.

Will definitely try Jimmy-D's solution!

Mike in CA

Bypassing the exhaust valves also came up when the 991.1 GT3 was introduced and I did a little research into the issue; I even posted a DIY on how to go about doing the bypass and ultimately switched the system back to stock.

Just FYI (and at least this was true with the 991.1 GT3) the bypass valves work differently than the ones employed with the sport exhaust on 997 Carreras and earlier GT3's. Unlike those cars, on the 991 GT3 the valves are modulated by the ECU so as to maximize low and mid range torque. In other words, while the earlier sport exhaust had no effect on performance, the later one does. If you disconnect them, you lose that functionality. The effect on power is real according to Porsche, but whether the difference is noticeable is a subjective matter. I thought I could detect a loss of throttle response which is why I reversed the mod.

FWIW, just throwing the info out there....

Jimmy-D

^I think Matt (Obsessed Garage) proved there is no affect whatsoever because he did them back to back on a Dyno. I love having them disonnected and for what it is worth; the 3800 rpm transition is so much more smoother and more subtle for some reason. Now- I had this done after switching to a GRP Bypass so could that be the difference and not the disconnection??

Mike in CA

Don't know about the GRP Bypass, Jimmy, although it is another variable in the equation. I've never noticed a problem moving through 3800 RPM although I always push the exhaust button before driving off so maybe that has something to do with it. I recall the dyno testing Matt did, but my butt and ear dyno still could hear and feel a negative (to me) difference so I wasn't convinced that Matt's dyno runs were accurately replicating on road situations. After doing the mod I really wanted to like the result, but I didn't. Anyway, I'm happy with the stock setup and the functional button and you and others are happy with the mod so TEHO!

ONEOFEW

Mike, thank you for the heads up, possibly altering the flow might affect the scavenging and efficiency of the factory set up. At least it's easily reversible.

Steve

RobbieRob

In Matt's car with the long tube headers, he is making so much more hp/tq(big increase in midrange) compared to stock or a center muffler bypass system, so Matt's car wouldn't feel or show the loss in midrange as much as a stock car or a center muffler bypass with the valves unplugged.

meaker

Matt did those Dyno runs when he had only a center bypass. I believe it was a GMG.

Mike in CA

That's why I took Matt's dyno results with a grain of salt. My thought is that any changes to the factory exhaust system would affect the factory parameters and programming for ECU control of the exhaust flaps. With my stock exhaust, defeating the flaps felt like a performance downgrade. With a non-stock exhaust there may be no difference whether the flaps are operational or not.

kblask

Would kill to have the Sport Exhaust button function the way it did in my old 981 Cayman S. Button deactivated, valves closed. Button activated, valves open. Permanently disconnecting the valves is too much of a commitment, as there are times that I'd rather be in stealth mode.

ONEOFEW

An interm device such as this possibly may do the trick it it's built for Porsche application

https://capristoexhaust.com/product/...-oem-capristo/

CAlexio

This excerpt below from the capristo website demonstrates why mike in Ca is correct that this mod can decrease performance and is therefore not a good idea if you care about that sort of thing

"The reason to have exhaust back pressure control is to obtain a better engine torque band and to maintain drive-ability in a wide range of conditions. Today,s high performance engines prefer a free flowing exhaust at wide throttle openings and high rpm. At smaller throttle openings and low rpm encountered in traffic, a slight increase in exhaust back pressure, results in better low end torque and a more user friendly engine.

This pressure is controlled by one or a set of butterfly valves in the exhaust system. These valves are in turn controlled by the engine ecu which would open and close the valves according to a preset set of rules. When using the vehicle on a track or in a sporty environment where it is desirable to keep the valves in an open position, a push of a button on the remote controller makes this possible."