resonator

[Eternal-X]

hey marvel.....
what is the purpose of resonator ?
does the size of the resonator makes a big difference ?
is it good if i eliminates the resonator ?
coz my supersprint'e resonator is twice as the stock one, and i feel like i lost power after i changed the resonator......

[MarvelPhx]

A resonator does exactly what it's name implies.

They simply modify the sound (resonance) of the exhaust tone. Removing or modifying them will only have the effect of changing what your exhaust sounds like. Unlike mufflers, resonators are hollow and are designed to act as a sound chamber. Mufflers are filled with sound-deadening fibers, perforated holes, chambers, etc to silence the exhaust.

BMW uses 2 resonators in the 330i to create the nice, musical stock exhaust sound. Aftermarket exhaust companies sometimes replace one or both of the stock resonators to create the exhaust sound they want. It is not detrimental to the operation of the vehicle. All true "exhaust performance" tuning is done in the manifold/header area. After that point, the best free-flow exhaust is your performance option.

Most manufacturers (including BMW) have resonators under the hood on the intake side of the engine as well. These extra pieces of the intake system are chambers or tubes that go nowhere, they just dead end. Their purpose is to create a resonation simliar to the engine. This resonation tries to cancel out the engine's resonation and quiet down the sounds coming from under the hood. They also have no real postive or negative effect on performance.

[Marky]

So,

If one wanted a sportier note coming from their stock exhaust, is it just a case of removing 1 or both resinators ?

How is this done ? Anyone got a step by step guide (pics?)

[MarvelPhx]

Define "sportier"...

[morcheeba]

I'm not an expert, but I'd think that the resonator does have some affect on performance.

Basically, you don't want the engine to be sending an exhaust shockwave out the headers that meets with a reflected shockwave from the resonator... otherwise, it would appear to be higher presure and thus a higher restriction (and less power).

The same idea works for the intake resonators - you want the exact opposite, where hopefully the resonator will generate a shockwave that travels down the intake headers at the same time the valves open. This shockwave of compressed air will act as a modest form of forced induction, adding power (this website claimed up to 15% more! (http://www.snowtechmagazine.com/articles/pipetemp/piptemp.html))

This website has pretty pictures of computer simulations. (http://www.mecc.unipd.it/~cos/DINAMOTO/risuonatore/risuonatore.html)

Of course, this does have something to do with noise. The ideal situations have no noise emmited; no energy is wasted and the resonator does a perfect job of matching the valve-controlled pulsating bursts of gasses to the non-pulsating (i.e. quiet) outside air.

Here's a quote I dug up from "Ricardo Information Services - Components News - July 2000 (http://www.ricardo.com/pressrelease/componentsnews.pdf)", page 18:

"An AZT paper from Friedrich Boyse GmbH describes an exhaust system with a Helmholz resonator and exhaust flap which aims to reduce the trade-off between sound attenuation in different frequency ranges and the reduction of power through exhaust backpressure. The use of a closeable flap improves the acoustic effectiveness of a muffler without worsening backpressure, and it is used, for example, on the VW Polo GTI and BMW 328i passenger cars. With the flap closed, low-frequency attenuation is increased in the lower speed range, while with the flap open, exhaust pressure and flow induced noise are reduced in the upper speed range. A muffler with gas flow is ideal for well-balanced ateenuation over a wide frequancy range. On the other hand, a branched or Helmholz resonator is suited to attenuation in the lower frequency range. A combination of both muffler types is used on the BMW 540i.
See Doc.107037. ATZ Worldwide, June 2000, pp17-19 (English text) & 426-432 (figures)."

It doesn't really say exactly why the flap is used, just it's effects. Does the closed flap affect the resonant frequency (which would have to change to match different engine RPMs), or just plug up the exhaust?

[MarvelPhx]

Helmholtz resonators are used in many applications such as automotive exhausts and fan intakes where noise emission reduction is necessary. When you blow across the top of a bottle and it "howls", you have created a Helmholtz resonator effect. Power is neither created, nor taken from the engine by these resonators. A lot of cars also have extra dead end tubes attached to their intake tubing systems; these are Helmholtz resonators designed to reduce intake noise.

The tailpipe "flap" you are referring to is strictly designed to control exhaust noise at idle/decceleration. It is too far away from the headers (where torque/backpressure tuning takes place) to make a power difference. It was originally designed to help allow the free-flow exhaust design of the 330i to pass the strict noise laws in Europe.

[JuN14sCR]

if the flaps were eliminated, would the car be louder?

[MarvelPhx]

At idle and decelleration, supposedly...