Intake helmholtz resonators – for sound or tuning?

[VeeFource]

Despite having researched into this, I can’t find any conclusive evidence of exactly what purpose these chambers serve depending on where along the intake system they’re based. Most agree if it’s before the throttle body it’ll be to mitigate nth order resonance at specific rpms. If its between the throttle body and air filter then from what I’ve read it’s to do with either sound and/or mitigating resonance to prevent the MAF sensor from reading incorrectly. However I can’t find anything on chambers that are upstream of the air filter in the snorkel.

Are these just to get past drive by regs or to stop droning at certain rpms when the intake can cause unpleasant sounding resonance in other structures which then feed in to the cabin? Or do these chambers still effect the very delicate tuning of the intake system of an n/a engine?

In one case I’ve seen the chambers claimed to enhance the sound of the intake:

http://aldousvoice.com/2013/01/07/ferrari-360-air-...

A lot of people seem to remove them claiming they’re just for drive by regs, but I can’t help but think it’s a LOT more complicated than that and all they’re really doing is causing flat spots in the rev range.

Any engine gurus out there?

[stavers]

Generally modifications to the intake system before the filter are for NVH issues at particular revs.

Having worked on engine development on dynos I can say for a fact that you want the absolute lowest pressure drop possible from atmospheric to the throttle (or atmospheric to the super/turbo inlet). There is no way that you would design an intake system for performance that had anything in front of the filter that would impede the airflow - therefore it is for noise.

From empirical data I have seen saving 1 or 2 kPa before the intake is worth between 5 & 10 kPa in exhaust back pressure with regards to getting more power from an engine.

[SuperchargedVR6]

My old Corrado VR6 had a resonator in the airbox exactly like the one below. When removed, the induction roar was ridiculous, and with no noticeable performance improvement.

[VeeFource]

stavers said:

Generally modifications to the intake system before the filter are for NVH issues at particular revs.

Having worked on engine development on dynos I can say for a fact that you want the absolute lowest pressure drop possible from atmospheric to the throttle (or atmospheric to the super/turbo inlet). There is no way that you would design an intake system for performance that had anything in front of the filter that would impede the airflow - therefore it is for noise.

From empirical data I have seen saving 1 or 2 kPa before the intake is worth between 5 & 10 kPa in exhaust back pressure with regards to getting more power from an engine.

Holy thread resurrection batman..

So when you say 'noise' do you mean to attenuate volume (for drive by reg's) or droney frequencies?

Where I'm going with this is, would removing the most upstream resonator give you more induction volume or just a less pleasing kind of sound?

[VeeFource]

Shame I never got an answer to this. I think a bump two years later is an acceptable one however..

[Krikkit]

Possibly better in the engine sub forum, but I believe they serve a dual purpose- the lesser one is to reduce noise, the other is smoother inlet filling across the rev range.

[GroundEffect]

They're mainly for NVH reasons. Help get rid of rush/whoosh noises. I haven't seen any data to suggest more performance from them - they're a bit far away from the intake runners to make a difference.

[NickGRhodes]

Sound and tuning.
Intake resonators are not just for sound reduction but allowing a reserve of air to help flow during the pumping pulses.

This link below is a good read.

http://planetsoarer.com/resonator/resonator.html

"Complete removal of the resonator saw a steady loss of power throughout the rev range of 4kW (7% loss!! peak power was 55kW). 5 resonators were tested, 245cc, 600cc, 710cc, 950cc and a 5000cc coolant bottle. 30 dyno runs showed a trend of small resonators best for high rpm power and large resonators good for low down torque with no straight line relationships between the different sizes."

It links to a good study on fluid dynamics in an internal combustion engine: http://planetsoarer.com/resonator/ResonatorsAcoust...

"It is evident that in presence of the resonator the fluid better follows the piston motion, while in the system without resonator the fluid moves with a lag that limits the mass transfer inside the cylinder."

Edited by NickGRhodes on Wednesday 5th September 23:04

[VeeFource]

NickGRhodes said:

Sound and tuning.
Intake resonators are not just for sound reduction but allowing a reserve of air to help flow during the pumping pulses.

This link below is a good read.

http://planetsoarer.com/resonator/resonator.html

"Complete removal of the resonator saw a steady loss of power throughout the rev range of 4kW (7% loss!! peak power was 55kW). 5 resonators were tested, 245cc, 600cc, 710cc, 950cc and a 5000cc coolant bottle. 30 dyno runs showed a trend of small resonators best for high rpm power and large resonators good for low down torque with no straight line relationships between the different sizes."

It links to a good study on fluid dynamics in an internal combustion engine: http://planetsoarer.com/resonator/ResonatorsAcoust...

"It is evident that in presence of the resonator the fluid better follows the piston motion, while in the system without resonator the fluid moves with a lag that limits the mass transfer inside the cylinder."

Edited by NickGRhodes on Wednesday 5th September 23:04

A good post there but then there seems to be a big distinction in the purposes of the resonators depending on whether it's upstream or downstream of the filter. There's been a few posts by others that state if it's they're located upstream of the filter then they're purely for NVH, but that they do effect tuning downstream and especially downstream of the throttle body.

But what I'd really like to know is are the upstream ones only ever generally for reducing resonances at certain frequencies in order to pass drive by tests and/or make the car as quiet as possible for the occupants? Or in the case of sporty cars are they only to smooth out the sound by reducing loud frequencies and boosting quiet frequencies through the rev range?

This is in an interesting article here about BMW's artificial engine sound which supports the potential on the latter question:

http://www.bimmerfile.com/2015/02/04/truth-bmws-ac...

[mwstewart]

SuperchargedVR6 said:

My old Corrado VR6 had a resonator in the airbox exactly like the one below. When removed, the induction roar was ridiculous, and with no noticeable performance improvement.

That's not a resonator, it's a bell mouth to improve air flow into the tube.

Here's a resonator on the bottom of the intake tube: