Air Intake

Why Install Aftermarket Air Intakes?

Give the engine bay a more dynamic look or as dress up item
Induction sound

[BSD] Intake modifications are to get more air into the engine. The engine management system picks the air/fuel ratio. The basics of the engine management system (at WOT) is:

Determine how much air is going into the engine at this instant (often by a Mass Airflow Sensor or speed/density system)
Determine what the best amount of fuel is for this amount of air
Inject only that amout of fuel into the intake air stream/cylinder
Determine what the best time to ignite the air/fuel mixture in the cylinder is (relative to piston position)
Ignite it
In some cases, monitor oxygen sensors to determine if we picked the right amount of fuel, then modify output as necessary

The point is that changing intakes, air boxes, cams, even adding superchargers and turbos is not to add more fuel or to change the air/fuel ratio, just to get more air in the engine. The electronics take measurements and then calculate and deliver fuel (and ignition). In fact, there is an optimum air/fuel ratio that does not change even when adding more air.

What Air Intake Mods Are Available?

Cantrell Concepts

Replaces stock intake tube from side air intake to air box. $325. Details at http://home.earthlink.net/~notslow/wsnE45E.html
[JH – 2001/10/06] I use the UNI OEM size filter and a Cantel style intake and think the sound is beyond reproach. Best sounding intake short of a 355 or 360, but does it make power? Maybe a little, but the sound makes it all worth wild.
[MR – 2001/4/16] I put the stock air box back in with the Cantrell Concepts duct. First, the sound. =) Very nice. Not overpowering, no whistling, just good solid intake noise. Only a hair louder than the shiny Dali intake, but it sounds a lot better. Next, the accelerations runs. It’s hard to tell anything conclusive. By this point I was probably down a solid 4 gallons from last night. Ambient still probably around 50-55 degrees. Last night, second would fluctuate between .35-.37. Today, it gave a solid .36 with the occasional jump up to .37 or even .38. It definitely fluctuated a lot less. I didn’t do any more 1/4 mi runs, just cuz I didn’t want to do them in broad daylight, and I’m also thinking I should be nice to my clutch and my S02s. My air filter for the stock air box is also pretty dirty. So, is it worth it? Hard to say for sure.
Pros: – Sounds good. – Fairly easy install (getting it seated into the rubber boot is tricky) – Does appear to give a little more power, however modest. – I’m a little concerned at whether this intake is going to cause me problems in the wet weather. The highways around here get a LOT of DIRTY mist kicked up when it’s drizzling, and that could do quite a job on the air filter. I don’t think I’d be able to get enough water in to damage the engine, though.
Cons: – It’s maybe a little pricey. – It’s not flashy.
If I wanted performance and sound, I’d definitely get one of these over a shiny Dali intake. If I wanted the look of a big intake, I’d get something else.
[DF – 2001/10/10] The improved sound is caused by the resonance in the intake tract, not by any increase in volume. Looking at the stock intake thingy, one can see it has an elaborate horn shape, apparently designed to minimize this same resonance. To each his own.
[SSJ – 2001/5/10]
I think Will’s air induction system works pretty well. I had it installed along with a few other unrelated items (SmartShifter and stainless brake lines) in my NSX and noticed a few noticeable improvements. Please note, I DID NOT perform a baseline dyno run or an after the fact dyno run. In fact, I have yet to even find one in Oklahoma. My impressions are STRICTLY seat of the pants.
The build quality is great – I received mine certified mail a few days after Will said he would send it. It came fully styrofoamed w/ a few Cantrell Concepts stickers and step-by-step installation instructions. The instructions included suggested use (read: don’t go thru standing water). OK already, you want to know if it performs and how well. Well, yes it does perform. How well, as determined by my SOTP feelerometer, is again subjective, but I think fairly well. I noticed an increase in throttle response especially above 30mph. The intake noise is more pronounced but certainly tolerable and perhaps more entertaining than stock. Almost certainly, you will notice better throttle response. I was pretty surprised with that performance characteristic. In theory, I think most of the HP increase would come at speed when any ram-air (not the strictest sense of the phrase) would take affect.
Overall, I think it’s worth the cost, especially compared with others, and I recommend it.

Comptech Uni Air Filter

Cleanable high-flow drop-in replacement for OEM filter. $80

Comptech Carbon Fiber Airbox

Uses the Uni filter element (above) with a carbon fiber cold air intake assembly.

$695 for ’91-’96, $725 for ’97+
[DLJ] I’ve had the Comptech Air Box on my car for a few days now, and can make some comments before my memory of the “old” car fade too far.
I’ve always admired how Honda made the car so silent, but I haven’t liked it, since the sound of a sports car engine winding up and down gets the old adrenalin-a-pumping.
So the first thing I did was to have headers and and HKS muffler installed. Then I took off the engine cover, so that I could at least hear the engine a bit.
The biggest change of all is the new Air Box! At 3,000 rpm with the throttle down, there is a deep baritone that I didn’t know the car had. And the “sewing machine” quality is gone. So is that sound above 5,000 that sounded like the GE turbofan on a 767 at take-off.
Between 3k and 5k, at full throttle, the air box is louder than the exhaust (of course the air inlet is closer to my ear).
I also put in the Comptech computer chip, and the transition to VTEC is now much *less* apparent. Before the engine was quiet until VTEC and the inlet lenthening cut in. Now it has the loud baritone smoothly through the region. Incidently, this is the first time that the car sounds like it has as much horsepower as it really has.
So, for me, this was a worthwhile addition. However, those that are interested in cost/effectiveness, should consider taking off that damping cylinder on the inlet. It would be an easy test, and could be reversed too. (see DIY – Air Filter and Intake for instructions on removing the intake baffle).
[SA – 99/2/22] I thought that that two most popular available airbox setups (CompTech and RM Racing) were differentiated by where they get there air from, CT from the side air duct and RM Racing from the engine compartment. Upon closer inspection, my CT Airbox has an opening on the front side of about 3-4 inches by an ince or two that allows air to come in from both the engine compartment and the side air duct, although it looks like most of the air still would come from the side air duct.
[SA – 99/3/12] There is a cool sucking sound under acceleration but no sound that I can discern (over my exhaust) while cruising.
[CCA – 99/2/24] If your car has a Comptech airbox thing be forewarned come filter element maintenance time:
The threaded receivers (for lack of a better term) that the screws/bolts (8 mm, 6 total) thread into (thus connecting airbox top to bottom) are attached to the carbon fiber bottom with little tiny pot-metal-like alloy rivets (2, each receiver). These are, shall we say, less than robust – they exhibit a marked tendency for failure when subjected to small amounts of pressure. Applying the loving little bit of massage that is required to release top from bottom can turn out to be not so good for thelittle guys. So pull your top out as carefully as you can, big daddy.
If CRRF (cheesy riveted receiver failure) has already happened, putting all back together again will present something of a challenge, what with the tight confines and required 3rd hand (the one mutation my dad didn’t give me), until one finds a new method of sticking receiver to bottom prior to mounting on top. Oh, and you must use two (flush) points of attachment per CRR as the twist of the bolt while tightening may otherwise spin the receiver round and round (CRRRaR). Whee.
Well, at least it took a little weight off of car (and wallet).
[JH – 2000/1/22] I installed a Comptech UNI filter in the stock location and used an NACA duct to pipe air directly from the outside intake. The Filter costs about $80ish and the NACA duct goes for about $40. There is also about 6-8″ of flex tubing between the stock air box and the duct. I have not dynoed it (although I am sure that it would show about nothing since there is no moving air)
The duct mates almost perfectly with the intake and is invisible from the outside. From a stand still, if you place your hand in front of the intake, you can feel suction. If you rev the engine you feel a lot of suction. 🙂 So at speed you should benefit greatly from this method.
Sound once the VTEC kicks in, IMHO kicks ass. Very throaty and has a nice even tone. (that may be due more in part to the filter, for some reason foam filers seem to make the smoothest noise as opposed to a K&N filter)
Mid to top range kick feels better, about the same low end. For the rainy season this filter setup kinda sucks. I have to dissconnect the flex tubing and redirect it so I don’t suck up water. The ONLY downside I can see besides increased filter maintinance due to increase flow.
Reason I mention this setup, apart from letting you folks know there is an nice, cheap, and easy way to get cold air into your intake is that you can run this with your stock filter and the $40 you wanted to spend is about how much it costs w/o the UNI filter.
BTW: Comptech cliams a 3-4 HP increase from just the filter and as far as intake temp drop I would expect no more than 10-20 degrees since the stock intake track pulls air from the wheel well anyway. This system just provides a more direct rout.

Dali Racing

Dali sells the K&N drop-in filter (below) for $50 – retail is $80.

K&N Drop-In Replacement Filter / K&N Cone Filter Charger Kit

“With the K & N Filtercharger?, a special cotton fabric is sandwiched between the pleated aluminum screen wires. The pleated design provides five times more filtering surface over the element circumference. The cotton/screen wire filter media is then saturated with a formulated air filter oil. More air flow, increased horsepower, long lasting performance – even after 35 years, the K & N Filtercharger? is still on the cutting edge of air filtration technology….” http://www.knfilter.com
[NM] K&N Filter ($65): My old filter was dirty and my expectations were low but the car does seem a little quicker. Also – sounds great with the engine cover removed. I found that Imparts sells these for approx.. $65 – which is a great deal.
[AWN] A few years ago, someone started circulating a story about a test of K&N filters that showed that they filtered much more poorly than standard filters. That story was later proven to be a hoax, but it still shows up on the automotive newsgroups and mailing lists whenever the subject comes up. Until I see the results of a REAL test that shows poor filtering by the K&N filters, I’ll continue to believe that they work just as well or better than conventional filters.
I don’t think they filter any less effectively than conventional filters. I’ve got a pair of K&N filters protecting the expensive engine in my Porsche, and oil analysis hasn’t shown any increased levels of silica or accelerated wear.
And for those of you who don’t know how K&N filters work…
Unlike conventional (dry) air filters, which trap particles in a mesh of tightly-packed fibers, the K&N filters work by trapping particles in oil. The cotton gauze in the K&N filters is only there to hold the oil and direct the incoming air across it.
The advantage is easy to see: For a dry filter to trap a particle of a particular size, the spaces between its fibers must
be smaller than that size. The K&N filter, on the other hand, can have much LARGER spaces between its fibers… So long as the incoming particle just TOUCHES the oil on one of the fibers, it’ll be trapped.
Therefore, the K&N filters can flow more air while still trapping just as much dirt as dry filters.
Also, as the dry filter fills up with trapped dirt, it flows less air and filters less effectively. In the K&N filter, the
trapped particles tend to sink down into the oil after they’re trapped, leaving fresh oil exposed to the incoming air… So the K&N filter tends to remain effective even as it collects dirt.
Cleaning the K&N filters isn’t all that hard. You just drench them in K&N’s cleaner, let them soak in water for a while, and shake them a little. After cleaning, of course, you have to respray them with the K&N oil.
Besides, cleaning only needs to be performed about as often as you’d replace a standard filter; I do mine once a year.
[DB – 99/4/5] K&N filters work very well IF you keep them cleaned and oiled with their special formula stuff. If you are not 100% positive that you will never ever disregard the manufacturer’s directions for cleaning and oiling, don’t buy it.
[TMI – 99/4/16] Tried to use Paragon that is recommended on the FAQ. Asked if it was in stock and when it would ship. They said same day. Got a bill a week later and they had run my card. When I called Jason he said that they we’re out of stock and one had been drop shipped from K&N. He would call back in an hour with a status. He didn’t call back so I called him the next day and he said K&N never shipped. Very frustrating when I had carefully done the “don’t put it on my card if you don’t have it” drill.

RM Racing

Intake $255

Intake + Cold Air $345

Cold AirOnly $165

Actual cone filter element is K&N
RM Racing Carbon Fiber Air Intake features funnel ram filter, three inch carbon fiber tube, with polished stainless steel hardware.
RM Racing Cold Air Intake Option. To be used with the RM Carbon Air Intake to allow direct air from drivers fender scoop. Installs easily with little mods. Keep in mind the filter will need more care due to added air flow.

Mugen Carbon Fiber Air Intake

This intake draws 100% cold air as it is connected to the opening on the driver’s side. A “Trumpet” Horn bell replaces the OEM resonator. The housing is made with racecar dry Carbon technology used in the F1 cars; the filter element has the largest filter area of any NSX OEM/After Market filters. Mugen is the premier Honda Tunning company. Add a dramatic look to the entire engine bay.
Cost about $1800

Additional Images

Gruppe M Carbon Kevlar Air Intake

Gruppe M intake add dramatic look to the engine bay.
Cost: $800~$850 new at Dali or SoS

Aftermarket Filter Warning

[A/H] Be aware that at Acura we have seen more aggressive ring/cyl-wall wear with aftermarket air filters. Mostly in Integras but we have had a few oil burning NSXs. If the air filter states to use a spray on oil, please use it. The air filter is there for a purpose.
This is the photo of the back side of the throttle valve. As you can see it is very dirty. I know only that it was a aftermarket filter. I don’t know what brand.
This is the photo that I will put in my report. If this car comes up with an oil consumption problem there will be no warranty.
To check your car, pull off the bellows at the throttle body, if it is a throttle cable throttle (pre-1995) then pull open the throttle and put your finger inside just past the throttle plate. Check for dirt/residue. You can use a mirror and a flashlight if needed.
K&N’s Response To Filtration Query
[LE] Since I have a K&N filter I contacted K&N to see if they could tell me more about it in light of the warnings from Acura. Here is the response. I have requested copies of the printed reports and will scan and post them as soon as possible. Keep in mind that K&N is only one of several companies producing aftermarket filters and others may have different filtration levels.
From:
Sent: Tuesday, April 13, 1999 7:51 PM
Subject: Re: Air filtration micron figures
Dear customer,
We stop 97% of particles on a 0 – 5 micron test. Paper rates at 98% and the OEM minimum standard is 95%. We have been in business for over 30 years and got started making filters for off road motorcycles. We even made the filters used on the helicopters in Desert Storm. As you can see, our filters have withstood the test of time and the harshed of conditions. Copies of the tests are available by snail mail only.
Thanks for asking,
Rick

Comptech Airbox vs. K&N FIPK

[BCH] I’ve made back to back tests with a Comptech modified air box using both stock and Uni filters and a K&N cone filter (which replaces the airbox). These tests involved taking the car out and really wailing it, not just a spin around the block. I found no detectable difference in performance changing the filter in the Comptech air box, but installing the K&N cone gave a power boost from 7000-8000 RPM (most detectable in 2nd gear). The airbox gives a deeper resonant sound which is less harsh than the K&N cone, but the K&N isn’t offensive. One note, when the air temp is over 75 degrees the K&N starts to feel the same as the other configurations, since it is sucking warmer engine compartment air.
K&N Filter kit, available as part No. 57-3502 from:
Paragon Products, Inc.
5602 Old Brownsville Road, F-3
Corpus Christi, TX
800-200-9366
361-289-8834
paragon@interconnect.net
It’s $159.95 if you say you heard about it through the NSXtra.

RM Racing Intake / K&N Filter

[AV] I have RM Racing’s Carbon Fiber intake that has a five inch long carbon fiber tube attached to a K&N type cone filter. I do not recall the exact brand but I have seen this in other speed shops and is said to be superior. It has a separate ‘cone’ that goes or sort of ‘folds’ into the cap end of the filter, effectively increasing surface area and shortening the overall length of the filter.
The sound is something I didn’t expect. A more throaty sound that is easily induced with slight pressure on the gas pedal. And more so with full throttle and when VTEC mode kicks in (definitely louder than stock). And not as much hissing as I expected (some hissing is present, though). I think that Carbon Fiber tube has something to do with it, some kind of resonant effect. I suggested to Randy to make the tube even longer for a deeper sound (if it doesn’t affect HP) but I don’t think there’s much room in the engine compartment.
I’m pleasantly surprised and very pleased with it.
[DNG] I had mine dynoed with stock airbox and RM Racing’s K&N cone filter. I GAINED about 4.6 HP peak with an average of 2 HP using the K&N. Done on the same day right after each other.

Homebrew Do-It-Yourself

[NM] It is a simple matter and very inexpensive. I found a “Pam Vegetable Oil” top that fit perfectly into this opening (no cutting or disassembly) and very rigid.
Pros:

Easy to install / No cutting
Better air intake sound – especially with engine cover removed for you coupe owners
[(drowns out the chattering sewing machine sounds).]
Easy to remove cap – although I did push it in there pretty damn good 🙁

Cons:

Next to no performance gains (by the seat of the pants) even with the K&N filter.
Having talked to others there may be a risk of allowing water into the airbox
[(seems unlikely based on the tortuous path, upward flow, and limited exposure to direct water).]

As far as CompTech solution – it is a similar ram design with a traditional filter / wider opening. I talked yesterday to a very respectable aftermarket NSX part dealer and in his opinion (based on dyno, development, and facts) there is next to no gains to be had modifying the airbox for the NSX. IOW the stock box dynos equivalent to any conceived airbox solution. Thus the CompTech box may not a very good use of $500 or Carbon Fiber.
Performance