Intake resonance is a factor, but one that's tricky to quantify, not least as there aren't many intake tests with back-to-back dynos especially vs anything other than the stock intake.


From what I can tell, intakes loosely group into two categories: Road and Race, with the former focused on the mid-range of each cam and the latter towards their top end. The confounding factor is exhaust resonance. Standing waves caused by reflections off the front face of the CAT create a dip in power around 4.5-5k RPM. It's first harmonic is 9k, coinciding with peak RPM, which is awkward for racing. As a result, systems either need to be optimised for midrange torque for daily driving like Mugen's or they are optimised for racing and peak around 4.5k and 9k, but require a decat/HFC/Gernpipe to avoid CAT reflections negating potential gains elsehwhere.
to Gurnby for finding this out and providing a solution (the GernPipe).

I believe that AEM style long tube intakes, generally peak around 4.5k and towards the top end ~9k, as a result of which you'll also need to replace your CAT for the full benefit. If you can play with its dimensions then you should be able to shorten it to drop its resonance to 3.5-4k for brisk daily driving.

Mugen's exhaust by contrast, is designed to resonate at 3.5k and 4k (and to a lesser extent about 5OO RPM either side) with a first harmonics at 7k and 8k i.e. it's tuned with a double-peak.

From what I can tell, many exhausts are symmetric with symmetrical backboxes equidistant from the center pipe. That means that they resonate in phase (and peak at the same RPM) leading to noisy exhausts. Most of the quieter twin exhausts by contrast have their centre pipe splitter mounted off-center leading to a more variable effect since the exhausts shift from constructive to destructive interference at different frequencies (reducing volume), while enabling them to tune for a double-peak resonance rather than a since one. (Double peaks are not necessarily broader overall, since a pair of high Q resonance peaks close together might be narrower than a single one with a lower Q.

I know you asked about intakes, but my point is that performance gains are maximised by a systemic approach. First decide where you want the power, resolve limiting factors such as CAT reflection resonance or aim for different RPM, fit an exhaust & manifold & tune your intake to match. Of course, you may get some gains with your intake at all RPM due to better flow (as with any straight through exhaust), but resonance is the more interesting question, so I thought I'd start there.

Here's dynos from a Mugen system, vs long tube & symmetric exhaust, and then vs a stock system:
https://www.s2ki.com/...st__p__23610353

 

No, not at idle. On a gas eingine you check at WOT, so I took it out and hit red line in third gear. That is how you use this gauge on a car.

zeroptzero,
I'll replace the air filter when the gauge reads 11" H2o. I have 82k miles on my air filter now and will replace it next Spring. I did a white glove test on my intake tube about 3 months ago and it was very clean(no dust or grime). When I do change out the air filter I'll take pic's of the old filter and the inside of the intake tube. The inside of the tube is not smooth the whole length, there is a ridge right in front of where I put the gauge. My S is a '06.

ROD

 

Thanks Rod, that is cool information, do you use a foam type filter or cotton gauze type ?

I've recently gone to a cotton gauze filter on my Mugen intake, I was a big concerned about the filtering capabilities of cotton gauze filters when it comes to dust, so I put a K&N drycharger pre-filter wrap over the filter.

 

If you track your car, any car you don't want any vacuum on the intake at WOT. On the street, 11" H2o might cost my (S) 8 to 10 HP at red line. I don't care about that little of a loss of HP on the street. A WOT romp up to 7250 rpm my air filter today goes to 5" of H2o vacuum but at 8000 rpm it still goes to 8"H2o. I don't think it will get to 11"H2o by next spring but I'll change the filter out do to time(years of service). But if I get in a dust storm(I'm out west and drive a lot in the southwest) this gauge will tell me when to change the filter out.

One more thing, if you change the filter out often you will introduce a lot more dirt into the engine. Over the life of a filter, about 90% of the total dirt that will pass through the filter will pass in the first 10k miles.

ROD

 

Thanks Rod, that is cool information, do you use a foam type filter or cotton gauze type ?

I've recently gone to a cotton gauze filter on my Mugen intake, I was a big concerned about the filtering capabilities of cotton gauze filters when it comes to dust, so I put a K&N drycharger pre-filter wrap over the filter.
[/quote]
I'm running a stock air filter. If I tracked my S I would run the stock air box but change it just a bit. Like take out that plate in the middle of the air box and run a much larger filter, also block off the stock opening on the air box. I would get a spare hood and then make a functional hood scoop.

ROD

 

Thanks Rod, that is cool information, do you use a foam type filter or cotton gauze type ?

I've recently gone to a cotton gauze filter on my Mugen intake, I was a big concerned about the filtering capabilities of cotton gauze filters when it comes to dust, so I put a K&N drycharger pre-filter wrap over the filter.
[/quote]
I'm running a stock air filter. If I tracked my S I would run the stock air box but change it just a bit. Like take out that plate in the middle of the air box and run a much larger filter, also block off the stock opening on the air box. I would get a spare hood and then make a functional hood scoop.

ROD
[/quote]

The stock air filter is my preference. You have 82k on a stock air filter ?, hot damn !

 

Check out these three articles related to the stock air box and modifying it. There's stuff in there about resonance, intake air temps, etc.


http://www.motoiq.com/MagazineArticl...r-Testing.aspx

http://www.motoiq.com/MagazineArticl...ng-Faster.aspx


http://www.motoiq.com/MagazineArticl...take-Mods.aspx

 

Interesting. Tough to beat the stock box as delivered, hacks and snorkels may be questionable.

It seems most advocate the benefits of a long tube style CIA (like AEM), because of the trifecta of smoothing airflow, colder air source and also the benefit of resonance tuning. This can all be BS, but I am willing to try it.

I have the parts to make my own intake coming, will let you guys know what happens.

 

I believe an intake can make a difference. I like the idea of making a 3.5" intake tube.

I have an FIPK, took a run with my friend in his CR when we were both stock (exception being my intake). We were dead even until we hit vtec, after that I pulled on him.

 

Best of both worlds! K&n intake with oem box. (Lid is off to show how it looks inside). Foam strip is around the pipe where the box and pipe closes and i have a snorkel on now. Since people say the k&n intake gains power and a oem box w/ snorkel gains power too, then im sure i definitely gain some power! Ill post a pic of my current set up soon