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997 GT3 Laguna Seca dB Sound Buster Modification - Beat the dB Limit at Laguna

If you have a GT3 or GT3RS, and race it at Laguna Seca, you might be black flagged for making too much noise. This is an issue even if you do not have a SharkWerks bypass exhaust installed (but it probably doesn't help your case!).

Luckily, there is a $5 fix, and it's documented here courtesy of SharkWerks customer, Mikymu. Thank you Mike for allowing us to repost this article in his own words:

Well, in 3 seconds flat if you don't count opening the vacuum cap packet. I don't know why this simple method escape my mind but after thinking through how the electronic vacuum switch work then everything makes sense. The electronic vacuum switch turn on the vacuum to close the lower exhaust flaps when 13V pass through it. When the electrical current is gone the electronic vacuum switch release the vacuum through a lower opening metal hose as shown below.



Plug up this metal hose then you will maintain vacuum ALL THE TIME and the lower exhaust flap remained closed regardless of RPM change or if Sport button is on or not. You do need to run the car with Sport button off first for 2 seconds to create the vaccum then your are good to go. This is super easy to do and you will pass 92 db sound limit at Laguna Seca. Sorry I did not think of this earlier but I will bring the packet of vacuum caps for those needed this Thursday at Laguna Seca

Of course those of you want to control the exhaust note at your finger tip can still venture the mod as follow: http://www.6speedonline.com/forums/g...inger-tip.html

Here is picture of the vacuum caps. $2.37 with CA tax LOL




Put the cap on the button metal vacuum release hose and you are good to go. You can install the cap without removing the electronic vacuum switch unit. Ignore my Jerry rigged wires for the other mod lol.

No more need to connect vacuum hoses together or any other cumbersome method just to track at Laguna Seca! I believe this method can be apply to other none GT3 models if you have similar vacuum switch.



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Archived Sound Buster Modification

Here is Mikymu's old technique if you prefer another version of the same effect:

Hey guys, I am a late comer as far as Shark Werks center muffler bypass. Alex had this fantastic product for a while and I have heard them on the track and it sounded flat out amazing when you step on the gas! I got hold of a set from Alex couple months back (sorry Alex it took me this long to post ... blame the kids lol) and like to share the simple DIY with few sound clips

Also, as many of you know that Laguna Seca has a sound limit of 92 db and OEM GT3/RS muffler set up will not pass even with sports button off. I busted the sound limit last time out at 95+ db with OEM muffler. Apparently there is a simple way to connect the vacuum hose as nicely demonstrated by Joe . This in turn channel the exhaust through all 3 chambers on the main side mufflers hence reduce exhaust sound significantly enough to pass the 92 db sound limit. But how does this affect the hp and torque? I will attempt to answer that question in this post.

OK, the Laguna Seca sound buster DIY lol

The principle is simple enough that your friendly Porsche dealer will charge $160 to route the exhaust through all 3 chambers on the main side mufflers by simply connecting two hose together. All you need is a 5/16" vacuum hose connector and two 5/8" corbin clamps to do the job. They can be had from any parts store and I got mine from Kragen for less than $5



The vacuum solenoid is located at the right side of the engine bay. The hardest part is removal of the OEM steel clamps - I sware, they are made out of titanium alloy or something. it was impossible to pry them open. I busted the head of couple small screw drivers to get them off. Now I can see why dealer charge $160. lol I am sure there is a special tool to do the job which will cost $398




Now all you need to do is connect both of these vacuum hose together and once you fire up the engine, the vacuum created by the intake will close the lower exhaust pipe on the main side mufflers and force the exhaust through all 3 chambers hence "muffle" the sound




Some dealer may use a different way to route the vacuum as shown below to achieve the same effect. It is a bit too much work and looks like they use another vacuum check valve (the white strip valve) to maintain the vacuum which is not needed since there is already a factory vacuum check valve on the left side of the engine bay. The way I have shown above will take less than 1 minute to switch out on the track and most importantly cost next to nothing to DIY




So, how well does Laguna Seca sound buster work and what is the reduction of sound in decibel? Sound energy degrade with distance and it's louder the close you are to the source. The intensity of sound energy degradation with distance depends on many factors such as density of air, temperature and source of sound wave etc. Below is a summary of the decibel difference between OEM and Shark Werks muffler bypass with and without vacuum valve and sports button ON. Both measurements were done 20 feet from the car with ambient temperature around 75 F in the late afternoon
  • OEM exhaust with muffler valve ON: 91.9 db
  • OEM exhaust with muffler valve OFF: 98.4 db
This Equal to 6.5 db reduction with muffler valve ON all the time
  • Shark Werks bypass with muffler valve ON: 93.2 db
  • Shark Werks bypass with muffler valve OFF: 105.4 db
  • Shark Werks bypass with muffler valve ON -- drive by test: 91 db
  • Shark Werks bypass with muffler valve OFF -- drive by test: 97.9 db
This Equal to 12.2 db reduction with muffler valve ON all the time at stand still and 6.9 db reduction with drive by tests. I had to warn my neighbor before I let the Shark Werks bypass exhaust rip ... and they LOVE IT!

As speedoflight has demonstrated that you can pass Laguna Seca sound limit with Shark Werks bypass as long as you plug in the vacuum hose and leave the muffler valve ON. But how does it affect the engine performance. My butt dyno says some lost of power in 4K to 6K range. let's answer this question in the proper scientific way .... let's DYNO!

I hooked up with Shad at Driving Ambition and used their Dynapack to answer the question. I meet Shad at Laguna Seca and they had an amazing twin turbo red NSX that pulled > 600 hp at the wheel and spun around Laguna Seca with a time of 1:30 .... OMG! The car pass me like I was standing still lol.

I decided to use Dynapack since you don't need to strap down the car and the Dynapack bolt right on to the wheels. For those of you new to dyno, it's best use is to help gauge the differences in hp and torque gain/loss with mods. It's not a tool to see how much hp you have so you can brag to your neighbor ... we will leave that to Dr. Porsche inc. lol




Shad's Dynapack setup gave consistent reading pulls after pulls with and without muffler valve on (sports button ON). Here is a video of the sound test and dyno



a clip of Speedoflight and I at Thunderhill



and the result .....


  • Shark Werks bypass with muffler valve ON: 221.4 lbft and 353.5 hp
  • Shark Werks bypass with muffler valve OFF: 238.6 lbft and 362.9 hp
This amount to 8.2 lbft of torque and 9.3 hp loss with muffler valve ON but most importantly 17.2 lbft loss of torque at 4300 RPM ... OUCH! Oh well, this the price to pay to play at Laguna Seca
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