The Physics Involved with Intake Design
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From: High Point
One restrictive looking part of the intake that ive noticed is the stock arm going from the throttle body to the filter. The crinks and ripples in it, would that be a restrictive piece as well. I have noticed that the CAI's totally replace that part, as well as the other "tube" intakes. What about this idea... replace that piece with a smoother pipe to the airbox, larger maybe if necessary and running the spoon snorkel? I guess like a ram air, to stock airbox (except the aftermarket filter, K&N maybe) to spoon snorkel. And as far as the scoop on the hood, i think thats a logical idea too, but please dont make it look so "Viper'ish", ive already heard people say it looks like a mini-Viper, which is cool on some points but not so cool on others. Gotta originate!! 
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From: Scottsdale
The thing about Fluent is that the person who sets up the model has to be very skilled to get results that mean anything. When I say skilled, I mean they have to understand the flow system so that they can set the nodes up properly.
If you don't set the model properly, then the results are junk.
If you don't set the model properly, then the results are junk.
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Joined: Aug 2003
Posts: 3,660
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From: Midlothian
Thx Silvershadow for your posts - a lot of work, and good solid info. I agree with what you have said about ail filtration, and that is one reason why I also plan to stick with the OE filters. Paper media filters have somewhat poor filtering until the large holes fill up, so that is why changing them every month is a bad idea. Of the 3 important fdiotration criteria, they do good to excellent in all three.
The downside of the gauze type filters (K&N) is that they flow great, but their claim that flow does not drop off because the filters remains permeable (the "rocks in front of a cave" analogy) does not really hold up. Plus, they let in a lot more dirt.
Foam should be ideal, as closed-cell foam theoretically should allow few particles of any signficant size to pass through without being trapped, and held, in the filter medium, But they do not seem to flow as well as a K&N, and often less so than a quality paper style filter. The Honda OE filter is very well made.
Foam and gauze oils can cause problems downstream, esp when the MAF is located quire lose to the filter. They can and do cause buildup of tacky glop on the mAF wire, causing driveability problems (at best) and up and down lean/rich cycles which can be dangerous (too lean).
Silvershadow (SS for short?) also confirmed my thought that laminar airflow is not often achieved in a car filtration system, and certainly not maintained for long even if it were obtained.
I believe a lot of thought went into the S2000 airbox; and yes, the boxes can be tuned using resoance techniques to cause a spike in air delivery. This is usually to fatten the torque curve, and the S2000 has needed some more of that from Day1. The whole design of the lid and the interior layout are as complex as I have ever seen in a car. If I had to speculate on what the engineering design team hoped to accomplish with the S2000's airbox it would be (in no order of significance):
1) More than adequate airflow for the engine's needs (that is, not modified)
2) Low noise, to comply with drive-by regulations in the US, japan, and Europe
3) Excellent filtration
4) Complete reduction in susceptibility to hydrolocking, and water damage to the filter medium - a wet paper filter, even treated paper, will allow a lot of damaging dirt to enter the intake.
5) No air rushing, resonances, vibrations, etc to the driver's ears
6) Long filter life, esp by ensuring that large debris cannot easily slam into the filter medium - if you open a "virgin" airbox at 20K miles, you will see sand, bits of pebbles, large bugs, all sorts of things you would not want in your filter
7) Adequate resistance to heat soak, as in-bay filtration must a must have
8) Ease of serviceability for technicians
9) Air horn to pull air in just in front of the radiator, at a low air pressure zone with some mechanical induction activity (slight ram effect)
Overall, I think they did a great job. And gutting the box to make it "look like it makes more pwer" may in fact either not achieve the result intended, or may just produce peak HP, with little or no benefits in the area below. Heavy mods might reduce 1 or more of the 9 benefits. Shadetree mechanics can do "gut feeling" mods, and sometimes they get lucky or, like Smokey Yunick*, they were blessed by God with amazing mechanical instincts.
The only mod I have made is putting in the Spoon snorkel. And after several days of driving, and everything settled in, I have a slight continuous drone in the 500 Hz range.
*Smokey's books are a must-read for any gearhead. His "Best damn garage in town" is full of wisdom, humor, strauight-talk, and kindness from one of the immortals of the American auto scene. I highly recommend them.
The downside of the gauze type filters (K&N) is that they flow great, but their claim that flow does not drop off because the filters remains permeable (the "rocks in front of a cave" analogy) does not really hold up. Plus, they let in a lot more dirt.
Foam should be ideal, as closed-cell foam theoretically should allow few particles of any signficant size to pass through without being trapped, and held, in the filter medium, But they do not seem to flow as well as a K&N, and often less so than a quality paper style filter. The Honda OE filter is very well made.
Foam and gauze oils can cause problems downstream, esp when the MAF is located quire lose to the filter. They can and do cause buildup of tacky glop on the mAF wire, causing driveability problems (at best) and up and down lean/rich cycles which can be dangerous (too lean).
Silvershadow (SS for short?) also confirmed my thought that laminar airflow is not often achieved in a car filtration system, and certainly not maintained for long even if it were obtained.
I believe a lot of thought went into the S2000 airbox; and yes, the boxes can be tuned using resoance techniques to cause a spike in air delivery. This is usually to fatten the torque curve, and the S2000 has needed some more of that from Day1. The whole design of the lid and the interior layout are as complex as I have ever seen in a car. If I had to speculate on what the engineering design team hoped to accomplish with the S2000's airbox it would be (in no order of significance):
1) More than adequate airflow for the engine's needs (that is, not modified)
2) Low noise, to comply with drive-by regulations in the US, japan, and Europe
3) Excellent filtration
4) Complete reduction in susceptibility to hydrolocking, and water damage to the filter medium - a wet paper filter, even treated paper, will allow a lot of damaging dirt to enter the intake.
5) No air rushing, resonances, vibrations, etc to the driver's ears
6) Long filter life, esp by ensuring that large debris cannot easily slam into the filter medium - if you open a "virgin" airbox at 20K miles, you will see sand, bits of pebbles, large bugs, all sorts of things you would not want in your filter
7) Adequate resistance to heat soak, as in-bay filtration must a must have
8) Ease of serviceability for technicians
9) Air horn to pull air in just in front of the radiator, at a low air pressure zone with some mechanical induction activity (slight ram effect)
Overall, I think they did a great job. And gutting the box to make it "look like it makes more pwer" may in fact either not achieve the result intended, or may just produce peak HP, with little or no benefits in the area below. Heavy mods might reduce 1 or more of the 9 benefits. Shadetree mechanics can do "gut feeling" mods, and sometimes they get lucky or, like Smokey Yunick*, they were blessed by God with amazing mechanical instincts.
The only mod I have made is putting in the Spoon snorkel. And after several days of driving, and everything settled in, I have a slight continuous drone in the 500 Hz range.
*Smokey's books are a must-read for any gearhead. His "Best damn garage in town" is full of wisdom, humor, strauight-talk, and kindness from one of the immortals of the American auto scene. I highly recommend them.
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Joined: Oct 2002
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From: Scottsdale
The only thing I would add is - I'm waiting for my snorkel from Muz as we speak.
Well I do have one more thing to add - there are two areas of concern regarding the design of the inlet air box
1. yes they did put on a good transition air horn at the inlet, and they have a smooth turn attached to the lid of the airbox - but the inlet looks small to me. I would estimate that the inlet is about 3.5" by 1.5 inches (If I weren't too lazy I would go measure it) for an open area of about 5.25 sq. inches. The velocity would be quite high entering the box at WOT and 9000 RPM - probably over 200 ft/sec.
2. The opening in the stiffener in front of the filter (OEM air box) looks pretty small, and I think they could put in a transition piece there that would smooth the air flow and reduce pressure drop.
Road Rage - do you have any information on the paper media that is used for filtration - who typically makes it, and what is the pore size (average or absolute) measured by bubble point? If I knew that kind of information, I could get a pretty good handle on the removal rating of the filter media.
PS thanks for the kind words, Road Rage. Like I say, this is the stuff I do for every project I get in. However, I do not deal with Helmholtz tuning, so I try not to say anything that will make me look stupid.
Well I do have one more thing to add - there are two areas of concern regarding the design of the inlet air box
1. yes they did put on a good transition air horn at the inlet, and they have a smooth turn attached to the lid of the airbox - but the inlet looks small to me. I would estimate that the inlet is about 3.5" by 1.5 inches (If I weren't too lazy I would go measure it) for an open area of about 5.25 sq. inches. The velocity would be quite high entering the box at WOT and 9000 RPM - probably over 200 ft/sec.
2. The opening in the stiffener in front of the filter (OEM air box) looks pretty small, and I think they could put in a transition piece there that would smooth the air flow and reduce pressure drop.
Road Rage - do you have any information on the paper media that is used for filtration - who typically makes it, and what is the pore size (average or absolute) measured by bubble point? If I knew that kind of information, I could get a pretty good handle on the removal rating of the filter media.
PS thanks for the kind words, Road Rage. Like I say, this is the stuff I do for every project I get in. However, I do not deal with Helmholtz tuning, so I try not to say anything that will make me look stupid.
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Joined: Oct 2002
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From: Scottsdale
So I'm laying in bed last night, and it hits me that the Honda engineers may have been trying to get some form of cyclone separation in the inlet. Hence the high air velocity at the inlet with the 90 degree turn right after the inlet. Any big stuff in the inlet air would be thrown to the outside of the turn, where it would drop into the first chamber.
HMMMM, I've got to look more closely at the inlet design to see if that's what they are doing. It would remove some of the particulate before it reaches the filter, prolonging filter life (see dirt holding capacity in my filter post).
I am going to be sooo impressed if Honda did that - that would be a pretty sophisticated design. (It's kind of like what we (the company I work for) do on turbine inlet filters).
Blitz - At this point I don't think drilling some holes would be the way I would go. It needs some further thought.
HMMMM, I've got to look more closely at the inlet design to see if that's what they are doing. It would remove some of the particulate before it reaches the filter, prolonging filter life (see dirt holding capacity in my filter post).
I am going to be sooo impressed if Honda did that - that would be a pretty sophisticated design. (It's kind of like what we (the company I work for) do on turbine inlet filters).
Blitz - At this point I don't think drilling some holes would be the way I would go. It needs some further thought.