Write-Up: Gutting the Stock Air Box

We used a K&N filter on our SuperHobby Chevelle I used to race. It had to be cleaned once a week because of the mud/dirt from the racetrack. Although I used the K&N oil after cleaning, I used a product like Simple Green or whatever I could find to clean the filter.

Bert

AA wrote:

quote: "Mist or drops will not be an issue."

Correct. Injecting a fine mist of water into the intake can actually have a performance-enhancing effect.

Anyone on here using alcohol/water injection on a Riv?

Bert

Quote :

Anyone on here using alcohol/water injection on a Riv?

https://rivperformance.editboard.com/search.forum?search_keywords=alcohol&show_results=topics

El_Riveriero wrote:

...the "bolt" on the front of the airbox, towards the bumper, was not a bolt at all. I just pulled up and popped the box off. then I pushed it back down and it popped back over the bolt.

That's a real good tip

With the rust problem people have in colder climes, and the fact that the rear bolt is 10mm so no one would think that a simple 1/4" socket would be nice and tight on the hidden, front bolt, I'm sure a lot of people have rounded off that sucker and had to destroy something to get their box out... I had no problem taking mine out today (Cali-car) but when I was putting the bolts back in I did notice that there was a lot more slop around the front one. Just now I went down and pulled the rear bolt out again and sure enough, I was able to pop the box's rubber grommet off of the front bolt without any tools! And a little spritz of oil, or even ArmorAll would make it even easier.

I have a couple of observations about the airbox for folks like me who want to free up the flow, but keep the noise down...

The red funnel in the lid is a definite baddie. Not only does it make the outlet of the airbox smaller and restrict the use of the air filter to about 1/2 of the panel, but it seriously isolates the IAT sensor from the airflow... When I removed it, my IAT when driving for a few minutes after a 20-minute heat soak was only 20 degrees above ambient instead of 60. When people remove the gray resonating cavities at the same time, they likely attribute all the improvement to opening up the box's intake openings.

After running with just the red removed (and an oiled-gauze filter) for a couple weeks, I tried taking out the gray cavities today. I don't have the scanner right now, but I didn't notice any difference in performance, and instead of just the nice high-frequency blower whine coming out, it now puts out lower, "grindier" noises, too... I'm probably gonna' put it back after a few days' trial.

The final reason I don't think that there's much to gain by removing the resonating cavities is that I measured the size of the input - the gray rectangle - and the diameter of the MAF intake... The actual area of the MAF intake is about 1/4-square-inch less than that of the rectangle opening. That's not even counting the further loss to the MAF screen, and I wouldn't remove that with a K&N-type filter because some tranny's have been wrecked by over-oiled filters getting oil on the MAF-wire and screwing with the operation of the computer.

Take from this what you will, but I figured I'd put it out there...

Good points, Mark. Doing these kinds of experiments is how we learn new stuff. I can believe the grey plastic parts don't make a huge difference in air flow (relative to a fully gutted box). It may be advantageous to leave it in for those looking for a quieter ride. For really moving copious amounts of air, a CAI or FWI is in order, imo.

As for the MAF screen, leave it in for the reason it was intended: rectify the air flow so the MAF sensor can get a good reading. It also works as a blockade against large objects should they get past the filter (it can happen).

But the MAF screen won't help against an over oiled K&N filter. The oil will go right though and dirty up the MAF sensor. However, knowing what I know about how our engine, computer, and transmission work, I find it HIGHLY UNLIKELY that you could do any transmission damage from over oiling the filter. Engine damage technically possible, but still unlikely. Basically, if your MAF isn't reading right, it will cause the PCM to add more or less fuel than it needs for proper A/F ratio. This will cause the engine to run rough, sluggish, ping, or show some other symptom before you'd have to worry. I've ran a faulty MAF sensor before and experienced the result.

Contrary to popular criticism, K&N filters do not typically cause engines and transmissions to fail. Otherwise, they would be able to sell their product and maintain the OEM warranty. What happens is, you get some idiot who pours the entire bottle of oil on the filter instead of following instructions, and then complains because his car isn't running right. Now everyone thinks badly of the product when actually it's user error. You've used the Audi throttle episode as an example of how this kind of thing can happen. I think K&N's reputation is very much the same.

AA wrote:

Good points, Mark. Doing these kinds of experiments is how we learn new stuff. I can believe the grey plastic parts don't make a huge difference in air flow (relative to a fully gutted box). It may be advantageous to leave it in for those looking for a quieter ride. For really moving copious amounts of air, a CAI or FWI is in order, imo.

As for the MAF screen, leave it in for the reason it was intended: rectify the air flow so the MAF sensor can get a good reading. It also works as a blockade against large objects should they get past the filter (it can happen).

But the MAF screen won't help against an over oiled K&N filter. The oil will go right though and dirty up the MAF sensor. However, knowing what I know about how our engine, computer, and transmission work, I find it HIGHLY UNLIKELY that you could do any transmission damage from over oiling the filter. Engine damage technically possible, but still unlikely. Basically, if your MAF isn't reading right, it will cause the PCM to add more or less fuel than it needs for proper A/F ratio. This will cause the engine to run rough, sluggish, ping, or show some other symptom before you'd have to worry. I've ran a faulty MAF sensor before and experienced the result.

Contrary to popular criticism, K&N filters do not typically cause engines and transmissions to fail. Otherwise, they would be able to sell their product and maintain the OEM warranty. What happens is, you get some idiot who pours the entire bottle of oil on the filter instead of following instructions, and then complains because his car isn't running right. Now everyone thinks badly of the product when actually it's user error. You've used the Audi throttle episode as an example of how this kind of thing can happen. I think K&N's reputation is very much the same.

I agree with you about it mainly being operator error, not the product itself (and I'm still using it.) I just wanted to list something to back up my comment about not removing the screen for better airflow, because I know some people do it. Your explanation about stabilizing the airflow is even better.

The Technical Service Bulletin itself cites over-oiling, and I imagine a way-out MAF reading would combine with other inputs like the O2 sensor, tach and TPS to "confuse" the PCM, and possibly cause shift problems. Of course, they may just be trying to get out of warranty repairs, too...

The title of one of the TSBs I saw is:
Automatic Transmission Shift, Engine Driveability Concerns or Service Engine Soon (SES) Light On as a Result of the Use of an Excessively/Over-Oiled Aftermarket, Reusable Air Filter #04-07-30-013A - (Jan 25, 2005)

98riv wrote:

I would remove the grey piece if you haven't yet. As Racingfan said, the only way water will get to your filter is if you drive through a 2ft puddle and then you will have other problems. I noticed more a difference removing the grey piece then removing the red piece in my car.

i just gutted my air box but i cut the grey piece down to about an inch tall and then cut the ribs out instead of just throwing it away it helped hold the lower box in the fender well better (more secure)

wootzgarage wrote:

98riv wrote:

I would remove the grey piece if you haven't yet. As Racingfan said, the only way water will get to your filter is if you drive through a 2ft puddle and then you will have other problems. I noticed more a difference removing the grey piece then removing the red piece in my car.

i just gutted my air box but i cut the grey piece down to about an inch tall and then cut the ribs out instead of just throwing it away it helped hold the lower box in the fender well better (more secure)

How does it sound?

I finally got around to gutting the air box. Piece of cake. The 99 only had one bolt holding the lower half of the air box to the inner fender. The other retainer just pulls out and pushes back in, no problem.

It seems to me like it somehow increased low RPM throttle response and it feels like it might have a bit more Torque. It could just be perceived and not real though. The wife walked outside and caught me. She saw me take my foot and try and move the resonator that was laying on the ground so she would not see it.
I was going to do the mod and not tell her to see if she noticed anything and mentioned it...

Its too bad nobody has a Chassis Dyno to document the results. All they would need is a gutted and a non gutted box to compare.

Bert

i gutted my air box notice it sounds lovely service engine light is on now tho v_v......

simba wrote:

i gutted my air box notice it sounds lovely service engine light is on now tho v_v......

check to determine whether you accidentally damaged the wire to the air sensor that's in the top of the air cleaner chamber. Do you know how to do that?

go someplace that will read the code and reset the light for you - autozone for instance.. While you are there find out what the code i, may be an unrelated problem.. Like for instance if you leave the gas cap loose the light will come on.

Albertj

thanks..........

albertj wrote:

check to determine whether you accidentally damaged the wire the ot air sensor.

go someplace that will read the code and reset the light for you - autozone for instance

First, check to see that you reconnected the Intake Air Temperature sensor when you put the air cleaner lid back on...
I always forget to do it - until I've "seen the light."

yea i 4got 2 plug it back in....lol ^0^

Like I always say, start with the simple stuff...

See how valuable advice can be from someone with the right combination of talent,
experience, and advancing senility?

Yesterday I decided to gut the airbox in Melissa's riv. Her riv is going to be staying stock-ish. It's incredibly easy to do and the gains are well worth the few minutes it takes. I ended up cutting the airbox for added airflow and it still took less than 1h. Aaron's write up is pretty much spot on. There's no need to expand on it, but here are a few observations and step 2A - swiss cheese the box


Why would you want to make a swiss cheese airbox ? Here is how your OEM box looks:

LID (TOP)


BOTTOM


The red piece seriously restricts flow. Just pry it off and you've removed a considerable restriction in the intake path. You can now take advantage of the entire 9.8cm (3.85") diameter of the airbox lid's outlet. The inlet duct elbow is actually fairly well designed. It's large and fairly smooth, except for the bend, with a fairly smooth curve radius.

LID (TOP)





This is how it sits in your engine compartment





The opening of the grey silencer is 6.5cm x 8cm (2.5" x 3.15"). The air filter is 25.4cm x 18.5 cm (10"x 7.3") for a surface area of 469.9 cm^2 or 73 in^2



This is your engine compartment with the grey Helmholtz resonator still in




Note how the stock airbox only draws air from the side, via the grey silencer. As air is drawn into the stock box and over the grey cavities, the resonance eliminates "undesirable" frequencies in the intake sound. It's been mentioned that it isn't the main restriction in the airbox. If you're not cutting the airbox, I suppose you could always just cut the whole top of the grey resonator off, leaving only the baffles in the hole, but I chose to take it out because 1) the sound doesn't bother me 2) with the front of the box cut the airpath is changed. the silencer becomes a restriction and it's usefulness is clearly decreased.

The idea behind making a swiss cheese airbox is to increase the area of exposed filter and remove restrictions from the intake tract while preventing the ingestion of hot air. By cutting the stock box, you are allowing the car to draw air from behind the headlight, but still preventing most of the hot engine compartment air from being ingested.







step 2A - swiss cheese the box

tools (required for steps 1-3):
ratchet set & extensions
10mm socket
1/4" socket
flat head screwdriver or prying implement
dremel or grinder w/ cutoff wheel
sandpaper
safety glasses

-Using your dremel or cutoff wheel, cut the airbox as follows:

FRONT:

SIDE:

BOTTOM:


- Use sandpaper or another dremel attachment to deburr the edges. This would be a good time to clean the lower half of the airbox.








-Reinstall the box




This is definitely a step up over the OEM setup and looks stock. If you have a stock riv, drop in a K&N panel filter (if you can find a cheap used one) or an accel Kool Blue. The Kool blues are 20$ on ebay, and a paper filter here is about $13.

the main restriction now becomes the stock size panel filter. The size is adequate for a NA 3800. It's barely adequate for an elderly driven SC 3800 and definitely too small for a modded S/C 3800.

1) CFM required for a 4 stroke motor = CID x Maximum RPM / 3456
2) CFM required for a turbocharged or supercharged motor =
{CID x maximum RPM x [(lbs of boost / 14.7)+1]} / 3456

CFM Formulas for Filters
Flat Panel: Length x Width x 6
Universal Round Taper: (Base + Top) / 2 = A
Take A x Length x 6 x 3.14
Universal Round Straight: Diameter x Length x 6 x 3.14

*calculations taken from gnttype.org, which were provided by K&N

Jason wrote:

the main restriction now becomes the stock size panel filter. The size is adequate for a NA 3800. It's barely adequate for an elderly driven SC 3800 and definitely too small for a modded S/C 3800.

1) CFM required for a 4 stroke motor = CID x Maximum RPM / 3456
2) CFM required for a turbocharged or supercharged motor = Pounds of Boost / 14.7

Add 1.0 to this answer. This relates to #1

e.g.: (CID x maximum RPM x #2 ) / 3456

CFM Formulas for Filters
Flat Panel: Length x Width x 6
Universal Round Taper: (Base + Top) / 2 = A
Take A x Length x 6 x 3.14
Universal Round Straight: Diameter x Length x 6 x 3.14

*calculations taken from gnttype.org, which were provided by K&N

Jason,
I don't understand the above formulas for figuring out the size filter needed for my application and Mod's.
Is there any way to show the results of some of these formulas as it pertains to the 3800. And how do I know what formula to use with the mods I have done.
Based on your statements and the fact that I'm currently running a mildly modified air box and a flat K&N, I am not providing enough airflow.
Just need to know how to get there from here. And be able to purchase the right size filter.
Can you help me understand a little better. Thanks
Rick

the CFM of a k&n drop in panel replacement for the 98 riviera is 10"x7.3"x 6 = 438 cfm. The CFM of a paper filter would be LESS.

For your requirements, use the above formula.
CID = 231 = constant. AFAIK, no one is running a stroked engine.
Max rpm can vary with mods (better valvesprings) and pcm tuning
boost psi can vary with mods (such as pulley size, exhaust, etc)

Plug your numbers into the formula to see what you require.
For example if you had a 6000 rpm redline and produced a max of 10 psi of boost
CFM required for that supercharged motor =
{CID x maximum RPM x [(lbs of boost / 14.7)+1]} / 3456
{231 x 6000 x [(10 / 14.7)+1]} / 3456 = 673.9 cfm required

Of course you aren't always at max rpm or max boost, but it's still a good indication that the stock filter is considerably undersized for any type of spirited driving. That's why a lot of people who end up using a FWI report an increase in performance over a gutted airbox. If you're just drag racing, and heat soak isn't an issue, an 8" universal tapered cone filter attached to the end of the inlet duct elbow will outperform a gutted box.

just use the other formulas to figure out what size filter you need. K & N and S&B have all the specs listed on their website. I'm partial to S&B because they have an inverted cone in the tip, not just a flat piece of rubber. So you can use a smaller filter.

for example, an 8" long tapered conical filter with a base filter diameter of 5" and top filter diameter of 4"

(Base + Top) / 2 = A
Take A x Length x 6 x 3.14
(5+4)/2 = 4.5
4.5 x 8 x 6 x 3.1416 = 678.6 or pretty close to what a stock riviera requires.

a 7" S&B filter would also work, as I've mentioned in a previous post.

Boost is NOT a good indicator to use. More boost does not equal more airflow. Boost is a measure of restriction after the supercharger, not how much air it's flowing. The MAF tells the true story. Use your MAF max Hz and figure out how much air you are flowing instead.

I do not know offhand the airflow comparison to MAF Hz (which depends on what MAF sensor you are using of course) but that's the only way to really tell.

I would guess, since the formula is coming from gnttype.org, that the boost formula is based on turbochargers. Roots blowers have a totally different airflow model. Also, the formula would need to change based on cam and head porting, etc. all things which affect total airflow.

wouldnt the MAF hz vary depending on your intake setup and ambient temp?
for that mater, your boost would also vary depending on your intake setup and air temp.

do we know any of eatons calculations to find out how much air the blower in taking in at any given rpm?

why cant you just take the 231cuin of the motor and add the 90cuin blower? 321cuin
using this calculator for cfm:
http://golenengineservice.com/calc/calccarb.htm

we would need a filter/intake capable of flowing 558cfm right?

Rather than Hertz, I'd just take the grams/second readout from the PCM...

Also, it may be simplistic, but since the throttle body IS there, I originally
just compared the area of the air cleaner opening with the TB opening...

"The final reason I don't think that there's much to gain by removing the
resonating cavities is that I measured the size of the input - the
gray rectangle - and the diameter of the MAF intake... The actual area of
the MAF intake is about 1/4-square-inch less than that of the
rectangle opening, and that's not even counting the further loss to the MAF screen..."

I agree with Derek about using MAF (mass air flow) to ultimately determine how much air is being moved, rather than boost. I don't see how MAFF (mass air flow frequency) would matter. It should be irrelevant.

deekster_caddy wrote:

Boost is NOT a good indicator to use. More boost does not equal more airflow. Boost is a measure of restriction after the supercharger, not how much air it's flowing. The MAF tells the true story. Use your MAF max Hz and figure out how much air you are flowing instead.

I do not know offhand the airflow comparison to MAF Hz (which depends on what MAF sensor you are using of course) but that's the only way to really tell.

I would guess, since the formula is coming from gnttype.org, that the boost formula is based on turbochargers. Roots blowers have a totally different airflow model. Also, the formula would need to change based on cam and head porting, etc. all things which affect total airflow.

I agree, boost (or manifold pressure > atmospheric P) shouldn't be confused with airflow. I disagree that boost is simply a measure of restriction after the supercharger. If you're saying you can't use boost alone to measure airflow, you are absolutely correct. To imply that you should NOT consider boost in how much air an engine needs would be wrong.

The gnttype member was troubleshooting a problem when he found that the air flow he needed was more than his 9" filter could provide. K&N shared this information with him to help trouble shoot his problem. The information was posted with permission from k&n as guide on determining air filter size for a given air flow capacity. The formula is the same for supercharged and turbocharged applications. The formula is a rough guide for how much air your filter needs to be able to flow for a given engine application. It isn't a calculation of how much air your engine is actually flowing at a given time. K&N essentially used the theoretical airflow formula, which uses 100% volumetric efficiency (VE).

Mr.Riviera wrote:

wouldnt the MAF hz vary depending on your intake setup and ambient temp?
for that mater, your boost would also vary depending on your intake setup and air temp.

do we know any of eatons calculations to find out how much air the blower in taking in at any given rpm?

why cant you just take the 231cuin of the motor and add the 90cuin blower? 321cuin
using this calculator for cfm:
http://golenengineservice.com/calc/calccarb.htm

we would need a filter/intake capable of flowing 558cfm right?

It seems you're also under the impression that I posted a formula to calculate your engine's exact airflow at a given moment.

That calculator is designed for NA enines. It uses the same calculation for an NA engine as the posted formula for 100% VE. You can't add the 90cu of the blower because it isn't participating in the combustion. Keep in mind that typical NA engines have VEs that range between 70-95%. It IS possible in an NA engine to have a peak VE > 100%. Boosted engines have a VE > 100%, hence the (boost/14.7)+1 factor.

Eldo wrote:

Rather than Hertz, I'd just take the grams/second readout from the PCM...

Also, it may be simplistic, but since the throttle body IS there, I originally
just compared the area of the air cleaner opening with the TB opening...

"The final reason I don't think that there's much to gain by removing the
resonating cavities is that I measured the size of the input - the
gray rectangle - and the diameter of the MAF intake... The actual area of
the MAF intake is about 1/4-square-inch less than that of the
rectangle opening, and that's not even counting the further loss to the MAF screen..."

it's not as simple as just having an opening the size of the TB. With an uncut airbox, the restriction is probably imperceptible as the side opening of the airbox is roughly the same size. You will definitely see a gain in performance by removing it and enlarging the "hole" in the airbox, just as you will see one from going to a cold air intake setup. The MAF screen is a negligible restriction. It just straightens the airflow. There are no real-world gains to be had by removing it.

AA wrote:

I agree with Derek about using MAF (mass air flow) to ultimately determine how much air is being moved, rather than boost. I don't see how MAFF (mass air flow frequency) would matter. It should be irrelevant.

I suppose my post didn't convey my intent.

your engine may be capable of flowing X cfm but you won't obtain the best performance if your filter flows < X. You also don't need a filter that flows > X. So I posted a simple formula to determine roughly what flow capacity filter you should have (and by simple manipulations, what size filter you require). There's no doubt that these formulae have a fudge factor built in to make sure you err on the safe side: they are the max theoretical air flow of your engine

If you guys really feel like it, go out and measure your ACTUAL VE by measuring your actual volumetric flow rate. You could then buy a filter EXACTLY the size that your engine needs. Then you can buy another one should you make a mod that affects your VE. Or you can use a simple formula that can give you the max theoretical airflow of your engine and call it a day.

Jason and all who contributed to this topic,
Thanks for clarifying your position and more important to me the formulas and the reasoning behind it all.
I have always thought that my flat K&N replacement might be a choking point for my intake air volume but had no way to calculate other than seat of the pants or more expensively a number of Dyno runs.
I seem to be having an extremely difficult time lately, figuring out the logical and mathematical equations on my own.
Thanks again for thinking this through for me,
Rick