Dear Experts,

I have a 1996 Honda Accord
2.2 VTEC engine, 5 speed


On my Honda, the air intake is
a lot more complex than the old
American cars I used to work with.

Then, the round air cleaner surrounded the carb, and
the air went directly through the carb and
into the intake manifold. Simple.



Please see the pictures.

In the 1996 Honda engine compartment, there is the:
air flow tube, which connects the
air filter, to the
throttle (near the firewall)


There is also a
Resonator, which is

Honda Part No.: 17280-P0A-013
Chamber B, Resonator

You can see some schematics of the resonator here:

https://www.hondapartsnow.com/genuin...0-P0A-013.html
https://www.bernardiparts.com/Honda-...0-P0A-003.aspx


Here, you can also see schematics of the:
Air cleaner chamber, Air flow tube, and Resonator

https://www.hondapartsonline.net/oem...-17288p0a000//
https://www.hondapartsunlimited.com/...h-17252p0a000/


Does anyone know:

What is this resonator used for?

How does it work?



Thanks a lot!

 

It is used to improve the volumetric efficiency(VE) of the engine and also attenuates engine sound.

The resonator is actually called a Helmholtz resonator. It acts as an air spring.
When you hear that air intake sound from a vehicle with the factory resonator removed what you are hearing is actually the sound of inefficiency.
Not to be confused with the air intake muffler which is usually located before the air filter. Although on the Accords, IIRC, this also has a vacuum control for different rpm ranges.
It's about harmonics.
As the intake valve closes the inrush of air hits the back of the valve and causes a wave that heads back out the runner, into the plenum and back out through the snorkel, the resonator acts as a sort of damper that allows this wave to be reabsorbed and reused to actually push more air into the engine. This aids in increasing the VE of the engine, sort of a mini supercharging.
Tuning the resonator for a given frequency will allow the pressure wave to bounce back into the engine at a given time(specific rpm range). In turn this will boost VE which will increase engine torque output in that range.
Depending on what the manufacture deems to be the ideal harmonic frequency of an engine, or application, then the Helmholtx resonator will aid the engine in that time frame(rpm).
The good.
On a stock engine the resonator is tuned for a given rpm and helps boost power production in that rpm.
The bad.
We may not know, without measuring resonator body volume, what rpm the resonator is tuned to. One may think for peak torque output rpm, others may think peak HP, and yet the manufacture may have tuned it for ideal cruising rpm(which would be lower than peak torque) just to quell engine intake noise at that rpm. It would boost torque in that range, so not really a 'bad' thing just unknown.
The ugly.
Any modification to the engine, or engines operating rpm, can render the helmholtz unused for the new rpm range.

If you have ever looked at a 94-96 LT1 powered B-body, they have the 'home plate' resonator in the intake tract, yet the LT1 F-bods do not. In that case it is considered used more for sound attenuation than for power reasons. It also could simply be that the F bod could not fit the resonator and an F-bod owner would prefer the sound over the improved VE efficiency. Also with V8s they tend to just change the runner sizes to optimize torque output, the benefits form a helmholtz resonator may not be as effective powerwise(for the design/fitment/cost) on the V8s of this era that it would be on a 4 cylinder.

I *believe* a similar thing happened with the F22A1 powered Preludes, they did not have a resonator in the air cleaner to TB tube, but the same F22A1 in the Accord did. Among other things the Prelude had a differently geared transmission which would change the Preludes cruising rpm slightly. There were other changes, IIRC the F22A1 Accord was 125HP but the F22A1 Prelude was 135HP. Now I've heard this is 'just from' ECU changes That seems like quite a bit of HP to pickup, or leave on the table, for an otherwise similar engine. It would be interesting to see the torque curves of each engine. Unlike the B vs F bod engines, the Prelude and Accord are very similar chassis, so it would be interesting to see what changes contributed to the added power.

FWIW
When the airbox broke on my '95 nearly 20yrs ago, the option was either A. buy the whole airbox or B. buy a CAI intake for considerably cheaper.
Air intake sound was much louder than before when leaning on the throttle. More of an attention getter, but also it kept me in a more 'eco' mode as anytime the engine would get under a higher load the intake would make noise. Stay out of the noise, stay out of trouble, keep those MPGs up.
Then I replaced the exhaust with a larger diameter, this actually quieted the CAI system a bit, again less load on the engine, better scavenging(better VE?) Pretty shocking.
Then the trans took a dump, replaced it with a non-Acccord geared unit and the rpms were higher, but the engine was under less load, and surprisingly the engine was even quieter again.
I'll bomb up an onramp and it will be surprisingly quiet.

 

Amazing! I had no idea such a thing existed.

 

my 2000 accord 4 cyl. didn't have this resonator from factory. i got an air tube with the resonator from a newer model, shall i bother replacing it?

 

I have a 99 that did not have a resonator but the duct was cracked. I replaced it with one from a 02 that had a resonator, seems to work fine.
But Mike is exactly correct on the resonator function.
Soarer - The Intake Resonator
keep your air filter clean.
if the engine is stock buying an after market intake duct is probably a bad idea.

 

Hi Mike,

Thanks so much for the detailed and lengthy post.

It's a new concept to understand, thus my delayed response.

Another question:

So, does the resonator system work better than a
Honda that has been modified with a
cold air intake?

Thanks again!

 

The resonator has been tuned for the car from the factory to do whatever Honda deemed necessary, be it sound attenuation or boosting torque a smidge.

A CAI is an unknown unless the CAI manufacture has posted dyno results(or you've spent time on the rollers), and if you search for such things you are most likely not going to find any proper data. Even a decent company like AEM/DC Sports does not have any actual dyno numbers for their applications.
Hondas were popular in the mid to late 90s and then the F&F scene kicked in and there is quite a bit of rice still in the aftermarket.
One could argue that a CAI system improves airflow in the higher rpm range, but at what cost to the low end and midrange power figures.
I recall years ago a geocities site that had a few before after dynos with CAI/SRI vs stock intake. Most were worse and a few (AEM being one) were better at the top end, however a majority of them had a dip in power into the midrange.
AEM later came out with a 'dual chamber' intake. Does it improve on anything, dunno, AEM doesn't have any dyno results or even a statement just a sales pitch of...
Take note of 'designed' and not 'engineered'.

Problem with testing on dynos and on 1320' is these are usually WOT blasts. We normally drive at part throttle.
If your only modification is a CAI or SRI and nothing else, I woudl say it is not worth the change. If you have other modifications that have moved the engine out of its normal operating rpm or changed its VE then a SRI or CAI may improve on power.
I can say that an SRI will increase MPGs as hot air will require the throttle to be opened more, this decreases pumping losses on the engine reducing load on the engine.
If you like sound the SRI is your noise maker of choice.
If you just want a little sound then the CAI will be better choice.

 

Thanks again for another knowledgeable response!

 

More explanation of the resonator in this video
Quote:

Over here is an air resonator

Inside here is a vacuum actuated valve
that activates over 2900 RPM
to quiet the intake noise down

And going to the actuator is this vacuum line



Honda Resonator