mooty

i am not sure why it's bad. there's a thread on it somewhere on 997gt3 board.

Mech33

The plot thickens: looking at the Service Information Technik for the 991 GT3, it looks like it has a vacuum reservoir after all. So the question is, does this get routed over to the OEM valves through some switching solenoid system, and if so, can we rig some switches up to these wires to keep vacuum applied to the valves continuously? Or perhaps the vacuum itself could be routed to the valves with some physical valves under the car that you just flip to maintain valve vacuum...

Mech33

OK after a little more searching around, I am apparently very late to this party. There are some well-documented vacuum-based methods of holding the valves closed on the 997 by either manually connecting the vacuum reservoir to the valve lines, or by trying to manually override the PSE vacuum solenoid with a switch:

Manual vacuum re-routing:
https://rennlist.com/forums/gt2-and-...ix-how-to.html

Electrical switch method:
https://rennlist.com/forums/997-gt2-...2-seconds.html

Sooo... I wonder how easy it is to access these vacuum lines / solenoid on the 991? I'll have to remove the engine cover to find out...

SmokinGTS

My question is the engine was designed with this feature for a reason. If we defeat the system what happens to the engine i.e; does it run hotter, will the muffler get hot enough to start melting parts around it, what about the increased back pressure, what effect will this have on the engine. Just sayin.....

orthojoe

I think the concern with this setup is the increased amount of heat that is retained in the exhaust system which also happens to be close to the engine. The side mufflers are in an enclosed space and the heat dissipation more restricted as a result.

The ideal setup would be a switch to use just for turn 5 along with some turnaway pipes to get you down do 90dB

Mech33

According to those 997 GT3 threads, they dyno'd before and after the power loss when forcing the valves closed is only ~10 hp at high RPM, so it can't be a huge engine impact.

The other argument is that any other sound solution similarly adds back pressure (attaching supertrapps or additional mufflers to the exhaust exit), so this is unlikely to be worse than those.

IMO this system was likely designed for:
1) Sound (aggressive sound at full throttle while maintaining civility around town at part throttle / idle)

2) Some power increase (a bit less restrictive when open)

Mech33

Or how about a steering wheel mounted button that you press going into turn 5?

doubleurx

Or better yet, GPS activation....set it and forget it!

GregJGT3

That's good, so how about a "cone of silence" for the sound shack activated when each car goes by...

Mech33

That'd be a fun little project. I never actually get to do design work anymore... tempting.

One concern with electrical activation is triggering any diagnostic errors from the appropriate valve impedance not being present on the trigger wires.

You'd want to disconnect the ECU-side wiring dynamically so you don't drive the solenoid with 13V and fight the ECU output in the process, so perhaps relays would be needed to connect the ECU-side wiring to an equivalent impedance while the valves are forced shut.

mikymu

don't run the engine with exhaust valve closed all the time - it may create strain on engine at high RPM and also over heat the side mufflers. I seen people blow holes in the side muffler and exhaust pipe connection coming lose under high pressure and set their rear bumper on fire trying to defeat LS sound police. If you gonna defeat LS ( other than not going there which is the best solution. When was the last time you went to a concert or basketball game with 90 db sound restriction? ) best to fashion a switch where you can control the exhaust valve and switch to quiet through T5 and back to normal operation after T5.

TRAKCAR

Great stuff here

PierreTT

Yes, great stuff indeed.
Suscribed!

Mech33

Thanks for the input. Did you end up having issues with your valve override over time? I saw your threads from years ago about this. Any lessons learned?

Mech33

I've ordered an extra PSE control valve (item #1 in the below part list) to begin experimenting. With an extra valve, it should be easy to rig up an OEM-override to the exhaust valves by simply plumbing a bypass around the OEM valve through the extra valve.



I also purchased a basic GPS development board to rig up the location-based switching. With any luck I'll get this up and running in a few weeks. I think it'll be a fun project, so I'm going to try to make it happen. Stay tuned...