Definitive answer on the Hermann von Helmholtz resonator?

Hi all! Have been in two minds about removing my Helmholtz resonator for quite some time now, specifically because of this reference to smoothing the incoming air for the MAF to read: Can anyone share some insight? *cough* calling Porschetech3 *cough* I know the GT3 and Turbo don't have a resonator but that's a whole different setup. I know plenty of people have removed it but I'd like more information Thanks!

If you cap it off (orange cap mod etc) there is no effect on the airflow through the MAF, since the return tube from the intake hose is after the MAF. I guess removing the resonator entirely could theoretically change the airflow before the MAF but I've not heard of any problems with that as long as both the airbox and hose are capped.

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Correct, it uses the Helmholtz resonance theory to reduce engine intake noise. However the literature makes mention that it does more than reduce intake noise and helps smooth the flow of air. I guess the literature makes it fairly clear that its been put there for more than one reason, I think im in the ill leave it alone camp. Have you removed yours?

Mine's had a Helmholtzectomy. gone. No issues.

Hoping to gain at least +5hp from it Guess I wont know until I do it if there are any negatives. The 997 actually has a vacuum actuated resonator box that closes over certain RPM.

The only negative I�ve found from removing mine (and adding a fabspeed silicone intake boot) was a substantial decrease in gas mileage. Because now, I feel far more compelled to take the car into the beautiful music making rev range every now and again.

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LOL..OK I have the answer you are looking for. The Helmholtz resonator does smooth out the pulses and quiten the sound, but does not affect the TOTAL air flow, or the AVERAGE air flow. For instance full throttle at 7000 rpm would read 255g/s air flow for 320hp ,Helmholtz resonator in place. Full throttle at 7000 rpm without Helmholtz resonator would bounce quickly between 250g/s and 260g/s, same result. 320hp. It happens so fast there is no change in A/F ratio or timing. Same thing happens when using Helmholtz resonators in the exhaust to quiten them down, it smoothes out the pulses, but does not increase the flow, no extra HP. Intake and exhaust pulses CAN be used to increase HP as in timing the pulses to help evacuate the cylinders in header/collector design, and to increase cylinder charging by timing the pulses as in Variable Ram Tuning of the intake manifolds/plenums.

Awesome thanks all and Porschetech3 extremely insightful as always. So in summation, there is no negative affect by removing the resonator I'd say that's a fairly definitive answer! Im going to try and get one fabricated metal so I can use my original intake boot

Right !!. Like jllphan mentioned, the only negative is your fuel mileage will decrease significantly !! Especially if you don't have a real aggressive muffler and can hear the engine scream , you"ll be deep in the throttle and high in the revs all the time !! I liked the sound so much I went a step further in retrofitted the 991 "sound symposer" into mine to amplify that sound !!

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Tell us more please!!

The 991 guys are blocking theirs!! https://www.6speedonline.com/forums/...poser-mod.html

This is something I read a long time ago, but don’t remember who originated this idea. Instead of capping the hole and buying the over-priced replacement boot, you can put an old oil bottle cap in the hole upside down and use the factory boot from the air box to the throttle body. Castrol caps work well because it has a flange.

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Yea I know they are blocking it off !!.. IMO stupid. I love the sound !! I did some of these about 5-6 years ago I did some with Lexan heat shield and some with aluminum heat shield. I tested the temp against the factory box and above 40 mph they are the sametemp, below 40 or stopped the open filtered air would heat up quicker,but would cool off quicker once above 40. the factory box would take longer to heat up once slow or stopped, but would take much longer to cool off once above 40 again. On my design there isn't much to hold heat, just mainly the small aluminum MAF housing. On the factory box , all the plastic ducts and box would get heat soaked and take a long time to cool off.

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Correct! It was coined "the orange cap mod". Heaps of threads on it so the idea isn't a new one. I just don't trust plastic when its post the air box filter screen...

First one I connected the "sound sympose"r into the silcone elbow..

Niiiiiice, looks like you've spent quite a bit of time engineering that!! How does it work?

It works great !! No negative effects and the sound is awesome !! I nicknamed it the Banshee !!... I have a 99 Cab with full fabspeeds treatment, fabspeed headers, fabspeed x=pipe with 200 cell cats and fabspeed maxFlows, and prefer the sound of the my 99 Coupe with the factory exhaust and THIS intake setup .

Looks vacuum actuated too? Assuming that opens the valve at a particular RPM? What does that part do thats next to the vacuum unit?

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Yes it's vacuum actuated. The vacuum line runs to a electric/mechanical vacuum changeover valve that is controlled with a wireless remote to turn off or on. (but it stays on all the time..lol) It could possibly be controlled by RPM actuation like Porsche does it, but I see no instances where I would want it off. The remote control I put on was basically useless since I never want it off. It's hard for me to believe that the 991 guys block this off cause they don't like the sound. To each their own I guess !!

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It sounds like they are a different breed... No pun intended

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Definitely a different breed . I remember my first impression of the 991 back in 2012, I thought yes, they got the sound right on this thing, not loud or obnoxious, but powerful and exotic sounding, higher pitch and nice timbre. And the new GT3 is the same only a step above !!

I have the IPD competition plenum with the larger throttle body which bypasses the resonator. I removed the resonator box from the air filter housing and used a 50mm gripper plug to cap the hole. No issues or whatsoever.

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Porschetech3 is this image of a MK1 996 with a 997 engine and 997 deck lid?? I'm so confused!! Intake, power steering pump cap, fan and lid look 997 while the tail pipes, bumper overriders look 996!?

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Sorry for the confusion, yea that fist pic was not my car, just one I had installed the same intake and sound symposer on. I was having trouble loading the pics..lol That is a pic of a 997. I did a couple of 997's and a couple of 996's. The 997's have changed hands a few times but still have the "Banshee intake with Symposer" still installed, the 996's have not changed hands, one is mine, the second pic of the Polar Silver.

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Ahhh I see, interesting tail pipes on that 997 then!

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It's a bad angle, part of the tailpip e got cut off..lol

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lollllllllll

About the 991.. Emotion - Porsche Study in Sound The Porsche 991 911 system. The automotive engineer's vocabulary is typically broad and precise, which makes it intriguing to hear the word "emotion" used increasingly when new technologies are introduced. In the case of Porsche's new 911, emotion was cited by engineers as a key factor in developing the car's acoustic signature. "Sound was a major design and engineering focus," explained Wolfgang Hatz, Porsche's Main Board Member for Research and Development, who also heads VW Group's powertrain development. At a recent technology workshop for the 2012 Carrera and Carrera S, Hatz and other Porsche engineers noted that creating a unique sound quality "between the engine and the tailpipe" has been a leading criterion for the 911 ever since the iconic sports car's 1963 debut. For the new Type 991 series (see http://www.sae.org/mags/aei/10167 ), the development team focused on “mechanical engine sounds characterized by high frequencies with tonal elements” together with low-frequency intake noises. So significant is the 2012 car’s symphony as deemed by Porsche that the interplay between induction and exhaust was part of the car's design and engineering specification. Computer modeling mapping, as well as analysis of the configuration and dimensions of manifolds, pipework, catalytic converters, and mufflers, was carried out at the company’s Weissach Development Center. The required sonic profile had to satisfy all possible operating states—from engine starting and idling (conveying power without disturbing the neighbors) to wide-open throttle on a racetrack. The goal was not only to deliver the aural “emotions” expected of a 911 but also to provide the driver with feedback about the car’s mechanical status while meeting Europe's 74 dB(A) drive-by noise requirements. Electronically synthesized noise is not a Porsche solution, so the engineers developed a new Sound Symposer that is standard on both versions of the car. An acoustic channel picks up intake vibrations between the throttle valve and air filter and a membrane incorporated in the channel reinforces the vibrations and transmits them as an engine sound into the cabin. The system is driver activated or deactivated via a “Sport” button that controls a valve ahead of the membrane. The result is a direct acoustic link between the cabin occupants and the engine, providing optimal transmission of the load-dependent sounds. The sound of gearshifts can also be enhanced. The Sound Symposer incorporates a tunable Helmholtz resonator to achieve an harmonious sound pattern, damping out unpleasant noise occurring at around 5000 rpm. If the Sound Symposer is deactivated, an aperture in the air filter housing still allows the basic engine and exhaust tones to be heard—"because we don’t want it to sound boring!” explained Dr. Bernhard Pf�fflin, General Manager of the Noise and Vibration Department.

Awesome!

Interesting, BMW calls their Helmholtz box a "muffler-silencer" in the parts catalog. My e39 had one on the intake boot and while quieting intake wooosh, it got in the way of anything you�re trying to do on the driver�s side of the engine. If you want to remove the airbox, you either have to remove everything from the intake to the fender wall as one piece or remove the 'muffler-silencer" box which is a PITA. I guess BMW decided that the less genteel e46 owners didn�t need their wooosh silenced because the e46 part for the exact same engine, has no box. I went with the non-Helmholtz e46 intake boot.

Nice, would be ideal if there was a non muffler boxed intake! Im looking into something metal as I don't particularly like the idea of plastic because the box is after the air filter.

I found an old audio file from years ago when I installed the Sound Symposer from the 991 retrofitted to my 996 with my Short Ram intake on it, the microphone in my phone has a bit of distortion in it that's isn't there in actuality, but here is the sound from the intake when turned ON. Very quiet and stock sounding inside and outside ,when not deep in the throttle, but quit loud when hard on the gas even outside, but not near as loud outside as some aftermarket mufflers..

^^^ Sounds great! Had no idea you could retrofit a 996 like that.

That sounds excellent!!

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Thanks !! Yes it can be done, takes a good bit of fabrication, but I'm no stranger to fabrication of all types...lol Thanks man. I actually prefer this better than my 99 Cab with Fabspeed headers, x-pipe, and MaxFlow mufflers...

Here is a new take on the old "Orange Cap" mod. I used the cap from a quart of Castrol Edge and it fits perfectly. Invert the cap and insert it into the airbox. It has a slight rim which prevents it from falling in. It fits in snugly and the hose reattaches as if the cap isn't there.

At least it looks to be sturdier plastic!