DIY - Air Box Mod

[Truck41]

go get-em aggie

[Titan4x4Aggie]

oops, there was an error in my calculations. substitution error. i am correcting it, and adding a definitions section for the vaiables.

argument still stands. long snorkel results in torque / hp loss.

[Titano24's]

Hehe I gotta love it when people get ownd hehe, and as for ignoring your post, I think not. Others on this site are engineers as well, i'm not a mechanical engineer but an electronics engineer none the less, and to me this mod just makes plan common sense.



-Shane

[the head]

Well, I won't go into calculations and stuff like that (although I could) because the last time I did that it came across poorly. And I'm also a ME.

Anyway, if someone wants to loan me their stock, uncut snorkle, especially if you're willing to meet me at the dragstrip (Houston Raceway Park) - I'll play the substitution game with it and mine that has been cut down. I did this with the stock air filter and the drop-in K&N and found that with the stock exhaust the stock air filter got slightly better averages than the K&N did (do a search in this performance section). Once the Banks went in, the K&N slightly edged the stock air filter, on average.

Anyway, this is the best way to see what it really does. Those numbers don't lie and I can make a bunch (12 or more) of runs at the track rather that relying on 1 or 2 dyno pulls.

What would be really nice is if we could do this and also get my hands on one of the CAI systems out there to try. So if you're in the Houston area and are game for some live testing bring your $8 to the track for the gate fee, your parts, and I'll do the rest.

[Titan4x4Aggie]

~~~ Fluid Mechanical Analyis of Air Box Mod ~~~

Part I: The Air Intake Model (Picture 1)

In short, the air intake system of a vehicle can be viewed as an electric circuit, with the pressure differential (votage) driving fluid flow (current) across the air filter (resistor) and through tubing with associated head losses (wires).

At a known RPM, the engine is attempting to pull in a known amount of air (swept volume of cylinder chamber). To fill the chamber, air must flow past the filter and into the chamber. The resistance of the filter prevents the air from easily flowing into the chamber, resulting in a pressure differential on the two sides of the filter.

This pressure difference also acts on the piston head in the form of a vacuum force, resisting the connecting rod which is pulling the piston down (sucking in air). This resistance results in torque loss, since the vacuum force acts over a radius (distance from center the connecting rod is attached to the crankshaft), and Torque = Force * Radius.

Going back to the electrical model, the filter can be viewed as a large piece of wire, where R=C*L/A, where as the length of the wire increases, and as area decreases, the resistance increases. Same for the filter, where if you increase filter thickness or density and decrease the filter area, you get less flow and more resistance.

This makes sense, since if you have a larger filter, the air atoms (in layman's terms) can spread out and move slower, resulting in less pressure drop.

Flowrate (m^3/sec) = Area (m^2) * Velocity (m/s)

For the same flowrate, if area increases, velocity (pressure drop) decreases.

What does this mean? (My theory is) At lower RPMs (1500-3500) and 25%-75% throttle, you get better gas mileage since there is less pressure drop for the set flowrate. However, at higher RPMs (3500 - 6000) and WOT, you get more HP since you can acheive more flowrate through the easier flowing filter and subsequently pull a denser air (higher pressure) into the engine. That part is just my theory.

Part II: Increasing Exposed Filter Area (Picture 2)

Now, to answere the question of how shortening the snorkel allows exposes more of the filter to the air flow, take a look at Picture 2. Although the air can (and will) turn 90º as it flows out of the filter, it WILL NOT turn another 90º to flow back into the filter. Some sort of force would have to re-direct the air particles, and no force is available until the air hits the box wall.

At that point, the air has hit the wall dead-on, completely stopping its velocity, and turbulating inside the box.

But cutting the tube shorter, the air molecules only need to make one turn (NOT 2) to reach all areas of the filter, and even than turn can be less than 45º. If the air does impact the box wall, it will do so at an angle (not directly), and be redirected towards the filter.

[Gig'em]

Could someone please tell me where Aggies got the reputation for being dumb?
Great post Titan4x4Aggie. Scientific answer to back up what seemed to me like a common sense solution.

[the head]

I don't know where or who started that. Personally I have a lot of friends who are Ags and Horns. I never hold it against them. But everyone knows Ags are weird and Horns are prima donnas...

[SIZE=7]GO TECH !![/SIZE]

[Gig'em]

I'm going to bite my tongue.

[hawkeye680]

Hey, I just got an email from the parts guy at my dealership. I asked them how much that would be to replace the snorkel if we wanted to reverse the change. It is only $15.67, so you don't lose much trying it out.

[Titan4x4Aggie]

$12.54 on nissanpartsdistributor.com

http://www.trademotion.com/partlocat...12&catalogid=2

[pciley]

Is there any plastic baffling at the bottom of the box that could be dremel'd out? I have the Volant and honestly can't remember if I saw any baffles worth cutting or not. I have a spare snorkel if anyone is too timid to cut their's

[Titano24's]

Originally Posted by pciley

Is there any plastic baffling at the bottom of the box that could be dremel'd out? I have the Volant and honestly can't remember if I saw any baffles worth cutting or not. I have a spare snorkel if anyone is too timid to cut their's

There is very little baffling in the bottom of the air box. The only other place I can see a resriction on the stock airbox is where the breather hoses are attached to the intake pipe. Obviously this huge box hanging off the pipe is Nissan's attempt to keep intake noise down to a minium, unless its an oil catch can.......which I seriously doubt.



-Shane

[Hatchman]

Sounds like a cheap reversal to me, worth the risk... where's my dremel...

[goathead]

so, will the dremmel work like i was asking on the first page of this thread? i see no reason why not, providing that a person was careful making the cuts.

steve

[CarolinaTitan]

I used a dremel with no problems. Go for it !!