993C4

I've come across this name several times. What does it do? Does it re-create that classic induction noise found in an air-cooled 911?

Riad

Well, it actually eliminates standing waves at a certain frequency. I guess it could be used in a car engine to change the sound.

Here is the slot resonator that I built for my studio. The numbers are on the bottom are the standing frequencies that are eliminated.

lawjdc

Well, I'll drink to that!

BTW, my 997S doesn't have that "classic induction noise". Maybe I need one of those Heimholtz resonators!

MJones

The air filter of the 3.8 litre engine differs from that of the 3.6 litre engine
through an active on-demand resonance reservoir integrated in
the upper part of the air filter. This reservoir is activated
via a vacuum-controlled flap as a function of engine speed and using temperature compensation.
The flap operates in the temperature range between
32° and 86°Fahrenheit, opening between approx.
4,600 and 4,800 rpm and closing between approx.
6,000 and 6,250 rpm.
Opening and closing the resonance reservoir produces
an improvement in the intake noise of the
3.8 litre engine, particularly in combination with
the specific intake system of the 3.8 litre engine.

Rolf Stumberger

lawjdc
Every 997 S has the Helmholtz resonator built in .
To answer the original question, Helmholtz was a German physicist ( early 1800's ) who did research in acoustics. Basically , all modern loudspeakers are based on his principles.

As far as I know, the reason for the resonator in the Porsche is to LESSEN the engine noise by cancelling out certain sound waves, as riad stated above , to comply with German noise requirements.
If you want to test the theory , blow over an open bottle. Depending on the volume inside and the velocity over the top, the sound will change. ( you can fill or empty the bottle with a liquid to vary the volume )

In any event , if you want to increase the engine "noise" all you need do is to block off the small air intake hose which connects to the resonator and you will have a much throatier sound , especially starting at 3500 rpm and above .
I did it on mine and I love the sound . I would say it sounds about like a mild performance muffler .
Also , it does ABSOLUTELY NOTHING to the engine performance and if you don't like it , just remove the plug.( I poured some latex mold material into the hose, which can be easily pried out if not desired )
I think the Fabspeed "Cold air intake " does the same thing , except they give you a "smooth" rubber elbow for about $225 and a plug to prevent dirt from entering the resonator box.

993C4

Rolf,

Thanks for your reply. Very informative.

When you say increase 'engine noise', i presume you mean 'induction noise'
because the sound is coming from the air induction box, hence induction noise.

I was a 993 owner preiviously and I do miss the induction noise of a air-cooled 911, and since I switched to my 997C2S (with PSE), I've been rather dissapointed with the sound. Sure, the PSE sounds ok, but it's more exhaust noise than induction noise, which led me to research on after market intake kits.

This is when I found FABSPEED air intake kit which includes a silicon cap to cover the helmholtz resonator valve. I saw the video clip, and as with all sales pitch, it looked mighty convincing.

I have PSE on my car, and I believe that by activating the PSE, I'm doing something to the helmholtz resonator valve (not sure open or close). Can the intake kit and silicon cap be used in conjunction with the PSE system? Are there any ill efffects (ie damaging MAF or anything else?)

jcnesq

I don't think having PSE makes any difference with the resonator. I put the Fabspeed cold air kit on before PSE, and it made a noticeable and nice difference with stock mufflers. Then put the PSE on, so can't compare PSE with and without cold air kit. Anyway, no problems at all after probably close to 10,000 miles.

fokker

"In any event , if you want to increase the engine "noise" all you need do is to block off the small air intake hose which connects to the resonator and you will have a much throatier sound"

Is that possible on the 997 non S?
To modify it to get better sound in some way?

Thanks

Rolf Stumberger

fokker,
I do not know if the Standard 997 air intake is the same as the 997 S.
However , just look at it .
In the S , the main hose (from the filter box to the engine) has a small~ 2" dia. bypass hose which connects to the Helmholtz resonator.
Fabspeed and Schnell , replace the factory hose with a simple silicone rubber ellbow and give you a plug to cover the opening on the filter box.
Again, by simply closing off the resonator, you do NOT change any engine parameters other than the intake "sound" caracteristics.
To me, it definitely sounds better ,so go ahead and try it. If you don't agree , you can just switch back.

lawjdc

Just trying to inject a little humor in this discussion. My car had the red Fabspeed "cold air intake" on it when I purchased it, but the exhaust rattled on startup and the Fabspeed mod was removed in an effort to find the rattle. The rattle stopped when the standard exhaust was replaced with the PSE system. Was the rattle caused by the Fabspeed cold air intake? I seriously doubt it, but I haven't felt the inclination to spend the 10 minutes to put the Fabspeed mod back on. I don't think the Fabspeed mod adds any noticeable power increase, and the PSE has a wonderful sound when you open it up. Besides, its nice to be able to be able to quiet the PSE system down when you need to get somewhere in a hurry without causing a ruckus.

Rolf Stumberger

993C4 ,
The PSE activation is totally independent of the resonator activation , although both react to engine power settings( via vacuum and solenoid switches )
Again, if you disable the resonator you do not influence the engine performance in any way.

I did a little research on the Fabspeed cold air intake based on the apparent interest on the subject .
Fabspeed charges ~ $225 for their rubber elbow, while you can get an identical looking red one from Schnell for ~ $150 if you are inclined to try it.
Like I said above ,I just plugged off the bypass hose and I do like the resulting increased sound .
I left everything ( vac./solenoid etc.) connected , just plugged the hose .
Since I do not have the proper instumentation, I cannot dispute Fabspeed's numbers , but find it very doubtful that a smooth interior rubber elbow vs. the "almost" as smooth factory one gives the claimed power increase .
While I visited their web site, I also looked at the Fabspeed exhaust system components .
The numbers for the headers, cats, mufflers and air intake kit add up to an increase of over 50 HP .
Well, lets just say that I am a little skeptical .
If it only were that easy . But , even if true , lets keep in mind that no matter what anyone does to the exterior of an engine , even removing the entire exhaust system , the engine will still not produce any more HP. To get an increase in HP , you need to increase fuel combustion PERIOD .
What you WILL get , is the additional power(torque) to the rear wheel, which otherwise is used by the engine to push the exhaust thru its various components (mufflers etc.)
Just keep in mind that when you reduce the engine backpressure of a naturally aspirated engine, you will change the engine characteristics.
You will get the INCREASE on the high end ( ~6000 RPM and above ) but REDUCED torque on the low end.
Thats great for racing, but I rather have it in the RPM range I drive at 99% of the time . How often do you go over 6 K ?

I for one believe that the Porsche engineers had good reasons for designing their systems the way they did, for optimum overall performance .
That's probably also the reason why they designed the PSE system as it is .They could have made the bypass pipes a lot bigger and claimed a HP increase. Instead , they made sure that the pressure drop is about the same as thru the mufflers , just increasing the exhaust "sound"
(noise ?music ?) and thereby maintaining the same engine caracteristics .

In any event , ultimately it comes down to whom you believe . The Porsche research team engineers, or some pipe fitter who welds mufflers in his garage .

Sorry, I think I got a little carried away here . Lol

PV

For those who can read Dutch (www.porsche.nl) or German (www.porsche.de), you can read under 911 S engine details and air intake that Porsche is explaining that the resonator is both for a better filling grade and a better sound.

That same info isn't on the USA site as far as I can see.

drhendrix

hp = Torque*RPM/5252

So, if you increase the torque to the rear wheels, it is pretty hard to not increase the horsepower. I've had very good luck on my supercharged 330i, by replacing the entire stock exhaust system. Dyno hp numbers went from low 300's to mid to high 300's. Back pressure does affect how much fuel you can combust in the cylinders as it prevents efficient removal of exhaust products from a previous cycle, preventing more air/fule from coming in.

In general, you want the free-est flowing intake, exhaust, heads, cams with software to match to get the most out of an engine. Period.

Rolf Stumberger

drhendrix,
What is your point ?

TT Gasman

Give me a break, the real reason they designed the PSE was to maximize profits from the American market. The valves are cute but I don't think there was a whole lot of R&D, I hope I'm wrong.
At least on the 996, the workmanship looks like something a guest worker did in his garage.