DIY - Air Box Mod

[juma]

I just pulled the tube out of the airbox and put it back together. I had some rubber rings from a sewer pipe connection so I used that between the airbox and the fender well to seal it up a little. Its not airtight but I figure the air will still be pulled from the interior fender as air doesn't like to turn that easy. seems to run even better. juma

[TallTexan]

I usually do not make such mods without waiting for more info but after pulling my K&N and seeing all the dirt accumulating in the bottom 1 inch of the filter, I knew this can not be right. There is no other explanation than most of the air is going through that narrow part of the filter which can not be good for air movement. I decided I would risk the $15 part and used my dremmel and cut it back within one quarter inch of the case. Very easy. I can say that I can feel the difference , not just in power, but throttle response. For the skeptics, if it did not help, it definately did not hurt. I will check my filter later to see if a larger area is now used. I put the dirty part of the filter at the top so I can see if the bottom 1 inch again gets dirtier than the rest of the filter.

[phillipyang]

for the next airbox mod, we should create a 3-4" pipe coming from the outside instead of the 2.5inch pipe we currently have. Wouldn't that create more volume of air to enter through?

[juma]

Originally Posted by phillipyang

for the next airbox mod, we should create a 3-4" pipe coming from the outside instead of the 2.5inch pipe we currently have. Wouldn't that create more volume of air to enter through?

that's what I've been fooling with....I'm thinking now a piece of metal ducting 4-6 inch diameter squeezed into an oval. then cut the air box hole oval and put the ducting in and into the fender then seal up with silicone sealent. A big hole like that would help a lot and probably get close to a volant performance. juma

[CLASH4X4]

Originally Posted by Titan4x4Aggie

You said you were a mechanical engineer. I did a quick analysis using several variables to "prove" that shortening the snorkel will indeed add hp.

Picture 1 shows the analysis for a general air intake assembly and the equations associated with deriving a net torque value from air intake losses due to pressure drop across the filter.

Picture 2 is a comparison of how shortening the snorkel exposes more of the filter to the intake air stream and subsequently lowers torque loss (increases net torque).

How does picture 2 show the filter exposed to more of the intake air stream? They are seeing the exact same air stream (in volume) because of the intake tube diameter, only the air stream is now being allowed to "stir" more inside the airbox before reaching the filter. I'm sorry, but your diagram of technobabble does not prove anything. Please call and ask the Nissan engineers why the airbox is designed that way before submitting your "calculations" as fact. Also, there is a point where the restriction increase caused by the filter element itself is almost neglegable because of it's relation to the engine's force. Like I said before, it's about less turbulance and a cleaner flow. Moving the tube opening further away will at most just make more noise (resonance).

And please...enough with the "Owned" bull****. Some people need to grow up.

Also, I said I am a mechanical engineer because I am one. Shall we exchange business cards?

[ArkansasTitan]

It looks like it would work to me. I am not a mechanical engineer or an electronics engineer but I am a sanitation engineer.

[JMC]

Moving the tube opening further away will at most just make more noise (resonance).

Do you not think there is some gain in efficiency with this mod? The reason I ask If you took a hollow tube and stuck it in the corner of a box (like the stock air box is built) and compared it to one with the tube cut off do you not think there would be added flow?
I have an average speed of around 25 mph during the week just in city driving. My rig has 3.7k miles on it. I was averaging 12.6 mpg. After the mod I have been getting 12.9 mpg.

Im sorry, but I dont see how you figure we are all peeing up a flag pole here. There was a post a while back where a guy showed his time slips with a factory air element vs. a K&N drop in and there was a difference in his E.T. Now if this little bit helps why and the heck wouldnt cutting the intake tube and stop it from crashing the air into the corner of the airbox help the flow.... I am no engineer but common sense makes me think different.

[juma]

with the same hole size but reduced tube length and reduced need to turn you are getting throttle response improvement and low end torque which does feel good and perhaps at the top end a bit of horsepower. with the long tube and the sharp bend you had to get a stack of air moving and it had inertia that was a slight drag. A bigger hole in the airbox will yield even better throttle response, better top-end horsepower and some torque over the whole rpm range. I'm not an engineer but have just done this many times with the same result. If you really want to get the most, cut off your MAF sensor to about 2-3 inches long and attach directly to a cone filter and the other end to the intake for a straight flow. even with no cold air the truck will jump off the line like a cannonball. juma

[sc186]

an increase in fuel mileage does not always mean that a performance increase was achieved. in fact, in this case the exact opposite is likely true. Look at the mystical "tornado" fuel saver for example. It creates a restriction in the airflow and as a result saves you a few pennies at the pump. However, there is no free lunch. That fuel mileage increase comes from a decrease in power. Less fuel burned per engine running time( in our stock state of tune tune) equals less energy or power output. In my last vehicle, i was amazed when my feul mileage increase directly related to the amount i increased boost. At first i attributed this to the increased efficiency, but after a tuning session with a wideband and egt meter, i realized that an increase in boost meant a decrease in my injectors ability to deliver fuel.

Now this does not mean that i dont believe that a more efficient engine will save fuel while performing better, its just that one does not always mean the other.

The stock tube is most likely tuned to provide the least turbulent airflow for the air as it flows from a small tube at a high velocity to the large airbox. The closer you can introduce the high velocity air to the filter media, the less turbulence you will recieve and the less chance the air will have to create disturbances and nonuniform flow paths. Air does not flow as ideally as the illustrations on previous pages tend to suggest. That and the calculations assumed that all of the air was entering the filter media in one spot, when it surely does not, even though the bulk of the contaminants on the filter are located on the bottom near the tube outlet.

[sc186]

by the way. Thats just my take on things and is offered to show both sides of the fence. After all, i did the same mod on my truck months ago before getting the Volant setup.

[phillipyang]

[SIZE=4]I pull out the flame war card on all of you[/SIZE]

[sc186]

i thought that since we are all at least over 16, and financially able to afford such magnificent pieces of machinery as the TITAN that we were able to talk like adults and try to increase our intellect at the same time. My post is not some kind of caveman response intended to revoke a negative point of view, but rather is a challenge to others to step up to the plate and input some of thier expertise. As an M.E major myself, i fully respect the opinions of those around me with potentially more intellect. However, one of the most fundamental tools of knowledge is being able to contradict one another and challenge what we percieve as truth.

I want to know more!! Aggie and clash, along with others including The Head, let me know as scientists what you think. No butt dyno's please. Im hungry.
By the way. When everyone that complained about a concentration of debris at the bottom of thier filters, and did the stock tube mod checks thier filters in a month or so notices a biuldup at the top of thier filters. Dont say that i didnt warm you.

[the head]

Just a couple of cents worth and that's it from me.

The airbox mod was one of the first things I did to my truck. SC186 makes some good points but as Clash4x4 stated, we would probably have to ask the Nissan engineers what their end design was all about.

My personal opinion and it is just that: I think the tube is there for resonance (sound) control. I don't think it has as much to do with keeping velocity up to increase milage, but it might be a secondary thought. I think another secondary thought would be to keep water off the filter as mentioned previously as well. Performance-wise, I think it does help with air flow under full throttle/max flow conditions due the fact the air takes less of a turn to get from the fender through the filter element. To me, this is a basic fundamental of fluid dynamics and head loss. The approximately 90 degree bend with the tube in place to get to the intake tube leaving the airbox will cause a greater headloss than the 20 degree angle or so with the tubing cut off. As far as keeping it laminar in flow, I think the filter will change the airflow along with the bend to get into the tube, the mass air sensor, the accordian style stock hose after that, the trickle of crankcase fumes in the pipe, another 90 degree turn, followed by the throttle body "butterfly". You'll keep some of the flow going straight through but not all of it. So I don't think the tube leading from the fender to the element is doing much to keep it laminar.

If the system was maxed out for laminar flow it would be a straight shot from the grill to the throttlebody with a filter installed at the very opening in the grill to give the air time to straighten out.

I tried both the stock element and the K&N in the airbox with the tube cut. The K&N barely slowed the truck down in the 1/4 mile with the stock exhaust. With the Banks the K&N was a tad quicker. We are talking thousandths of a second here so there are so many variables to that, I don't know that it helps or not (probably not). I'm also not a fan of the butt dyno. I think that is 90% in someone's head. I put the Banks on and only gained 0.1 secs in the 1/4 mile. I can tell you I didn't notice a power difference at all. With the nitrous you can feel that but it is so minimal (with a 50 shot) that it's not exactly a set-you-back-in-the-seat kind of gain. You'd be surprised. Also with the butt dyno, if you make less power from a mod and then the truck pulls out of that dead spot, you'll feel that thinking it has addded power when in reality isn't any faster, it's recovering from a loss of power.

Dynos and track testing are the only things that are going to show anything. Even then, dynos are just a tool. Throw weight, traction, no correction factors for the atmosphere, and other odd variables (like wind for instance) into the mix and the track becomes the most realistic thing because it IS real. I do believe in dyno tuning but it should also be backed up at the track. Also, if you get something that is tuned within a short range of conditions, it may run crappy on the track/street but ran great on the dyno when it was set-up. Some of the Chevy guys have that problem with their tuning. If you've ever raced a 2-stroke bike you know what I'm talking about too.

So that's my take on stuff.

My offer still stands that I will be happy to "borrow" an uncut piece to swap in and out of my airbox to see if it works. I'm not going to spend the $15 myself to clear this one up because I feel that the cut tube works. I have no dragstrip data to back that since mine was already cut the first time I went out.

[Hatchman]

I did the mod. It is definitely LOUDER. Don't do this mod if you don't like a loud truck. There is a big sucking sound right when you hit the gas, and a big whoosh sound as it revs through the rpm range. Big words I'm using there, 'sucking' and 'whoosh', but those that did it know what I mean. Once at cruising speed, I can't tell any difference, but the moment you get back on the gas, you can hear it again. Sounds a like like an open cone filter, but with more of a resonating sound. Not too annoying, would sound better with an aftermarket exhaust to match it.

Can't really say about mileage or performance yet. Only have the butt dyno and haven't checked mileage yet.

[Titan4x4Aggie]

Originally Posted by CLASH4X4

How does picture 2 show the filter exposed to more of the intake air stream? They are seeing the exact same air stream (in volume) because of the intake tube diameter, only the air stream is now being allowed to "stir" more inside the airbox before reaching the filter. I'm sorry, but your diagram of technobabble does not prove anything. Please call and ask the Nissan engineers why the airbox is designed that way before submitting your "calculations" as fact. Also, there is a point where the restriction increase caused by the filter element itself is almost neglegable because of it's relation to the engine's force. Like I said before, it's about less turbulance and a cleaner flow. Moving the tube opening further away will at most just make more noise (resonance).

And please...enough with the "Owned" bull****. Some people need to grow up.

Also, I said I am a mechanical engineer because I am one. Shall we exchange business cards?

I dont even care anymore. All this is saying is that a free air box mod w/ drop in filter will yeild similar results to a $250 voltant.

who cares about proofs and what not. if you want to spend $250 for 5-10 hp, you have money to waste and no argument will coerce you otherwise.

i'm off to finish installing my amp and cap.