991 GT3 centre bypass

[terryb]

Harpersax said:

Anyone have any idea on noise levels of these with the valves shut?

Having only just got through the noise test at Brands this year with the stock system I’m a bit concerned a bypass might mean I fail in the future.

Thanks

No chance with Sharkwerks or any other bypass. The valves open above 4krpm even with the switch off - but they’re open all the time when on.

You’ll be ok for noise at Silverstone, Nurburgring, Spa and Donington Noisy days, Oh and Knockhill because the sheep haven’t petitioned the local council as yet

[Porsche911R]

terryb said:

. The valves open above 4krpm even with the switch off - but they’re open all the time when on.

they still close when on.

[chrisABP]

terryb said:

Harpersax said:

Anyone have any idea on noise levels of these with the valves shut?

Having only just got through the noise test at Brands this year with the stock system I’m a bit concerned a bypass might mean I fail in the future.

Thanks

No chance with Sharkwerks or any other bypass. The valves open above 4krpm even with the switch off - but they’re open all the time when on.

You’ll be ok for noise at Silverstone, Nurburgring, Spa and Donington Noisy days, Oh and Knockhill because the sheep haven’t petitioned the local council as yet

As Terry said if you have a bypass fitted you will struggle at most UK track-days except the odd noisy days and they are ok for most days at Nurburgring & Spa. The vast majority of Sharkwerks bypass pipes we sell are bought by owners who want more of the epic GT3 soundtrack (usually produced at 6,500rpm+) across a more licence friendly RPM range whilst being used on the road. In return you get more of the glorious noise without the big numbers on your speedo. Makes the ownership more enjoyable as a road car at usual road speeds.
As a previous poster has said its also quite straight forward to switch back to the OE system for the occasional track day but bear in mind there is the strong possibility on certain tracks, with certain weather conditions that even a stock GT3 can fail the stricter noise tests....

[terryb]

Porsche911R said:

terryb said:

. The valves open above 4krpm even with the switch off - but they’re open all the time when on.

they still close when on.

When?? At idle if you press the switch the valves open and the noise level increases. So when does the valve close when PSE is on?

[w5pwr]

The PSE shuts off between 45kph (28mph) and 75kph (47mph), the feature is there to comply with Euro noise abatement.

You can fit one of these if you want to override the feature...http://www.carnewal.com/products/981/p091/Installation-Set-for-Switchable-Exhaust-via-Remote

[short-shift]

w5pwr said:

The PSE shuts off between 45kph (28mph) and 75kph (47mph), the feature is there to comply with Euro noise abatement.

Is that correct? I thought that, with PSE activated (switched on), the valves are open at idle, close just after driveaway and open again at circa 3700rpm (engine-speed and load dependant, rather than road speed related)?

I thought that the legal requirement (noise abatement) need to be satisfied only in the default (PSE-off) mode - where the valves remain closed at and from idle and only open at around 4000rpm or above, dependant upon engine load and throttle setting (the more aggressive the driving style, the lower the engine speed at which the valves open).

So with PSE-on, where the legal requirements don't have to be satisfied, the main reason for the "open-close-open" sequence is to mitigate a pretty severe drone that otherwise happens at points in the 1000-3700rpm rev range with the stock exhaust system. I also understand that replacing the rear silencer with an aftermarket bypass can affect (sometimes reduce) this tendency to drone, with the effect varying according to the make and design of bypass that is fitted.

Am I right with this?

James

Edited by short-shift on Sunday 28th October 08:08

[Taffy66]

In my Gt3 when you press the PSE button the valves open when parked up, but close when you drive off..They open again at about 4k revs or thereabouts. IIRC the reason the valves close under 4k revs is to increase back pressure to increase torque at low revs.The valves reopen at 4k revs for more free flowing which increases power..

[short-shift]

Great - the functionality you are describing fits with my post immediatey above.

Interesting that you mention the back-pressure issue and impact on torque. I thought this was de-bunked by some rolling-road work that Matt (obsessedgarage.com) carried out a few years ago; I think he concluded that the back-pressure/torque issue had started as a forum comment that had been posted somewhere and which simply became a bit of GT3 folklore. He was pretty clear in concluding that the reason for the "open-close-open" sequencing of the valves with PSE engaged was simply for noise management (boom mitigation) purposes and was not related to impact on torque curves, performance or driveability.

Funny how this continues to go round and round...

James

Edited by short-shift on Monday 22 October 11:33

[Adrian-9iafn]

Yes I agree with this and have seen the obsessed garage video. I have not tried it for myself (keeping the valves open) but suspect the boom in all configurations would be annoying.

I would like to see how it sounds PSE off with a bypass ?

[S3RPM]

Where abouts are you Adrian? I'll be putting my Sharkwerks back on the car after Friday as I'm hoping to do the track day at Snetterton then. I'm in Norfolk.

[Adrian-9iafn]

Yes I agree with this and have seen the obsessed garage video. I have not tried it for myself (keeping the valves open) but suspect the boom in all configurations would be annoying.

I would like to see how it sounds PSE off with a bypass ?

[Juno]

Has anyone heard or have the Miltek option?

[BrntRubber]

Taffy66 said:

I'm in the process of fitting a centre bypass on my 991.2GT3..I want a Titanium one so i have been looking at JCRs, IPE and Akrapovic's new Ti centre bypass but my favourite is JCR if you take value into account..Akrapovic's new centre rear bypass is a work of art but pricey at circa £3k(including tips)..
I phoned my OPC yesterday regarding my RS allocation and happened to mention i intended to fit a centre rear bypass and he didn't see any warranty issues, as long as you don't interfere with the ECU..On a gen 1 i would make doubly sure because of the ten year warranty..

I have a soul bypass on the cheap to see how I like the sound and valve transition. Ultimately if I like more volume in the cabin, I will go with Dundon Motorsport when they release their inconel exhaust.

My London dealer said any exhaust mod has a big impact on warranty.

[CorrosionInhibitor]

Bit of a thread resurrection but does anyone have any systems for sale or know of any for sale before I take the plunge and buy new ?
Thanks !