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Old January 8th, 2013, 05:46 PM   #1
alex.s
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airbox volume calculations?

was wondering if someone in the know could offer some resources for calculating an optimal stack length and airbox volume for a given engine... @choneofakind?
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Old January 8th, 2013, 07:24 PM   #2
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the intake tract length was dependent on the rpm for each harmonic.
i believe chone used these two links to calculate intake length
http://www.bgsoflex.com/intakeln.html
http://www.swartzracingmanifolds.com/tech/index.htm


i ended up designing an intake with a length of 11 inches using the filter's inlet flange as one end and the intake valve as the other.... but i'm not totally sure that's correct.

not sure about the intake volume, but i'm guessing the more free flowing the intake is, the more powerful the harmonic action.
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Old January 13th, 2013, 01:27 PM   #3
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Last time I looked into that, I just used some of the online calculators. I came up with numbers that were everywhere from 8 inches to 11 inches... I understand the basic physics behind the resonance that you're trying to achieve by tuning the intake length from my phsyics lab and some thinking, but I'm not sure on the exact length that we need.

I also measured the distance from the end of my intake to where I think the valves are and it turned out to be 10.something inches? Sorry I'm not much help. I wrote it down somewhere and can't remember where

I might experiment with it later, but I have more important things to figure out first, like my fuel map and my ignition timing map. After those is tuning the intake length. BTH, I'm not sure how of an effect that will really have on the little ninjette though...
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Old February 6th, 2013, 07:34 PM   #4
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Bump on this thread. I did some more reading and I have a few articles that you might find interesting.

http://www.google.com/patents?hl=en&...onance&f=false

http://en.wikipedia.org/wiki/Inlet_manifold

http://en.wikipedia.org/wiki/Helmholtz_resonance
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Old February 17th, 2013, 01:16 PM   #5
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Another bump on this thread because I want to pick @alex.s's brain some more.


What if I kept my pod filter and 3" intake runners, but opened up holes in the front of the air box large enough to fit the clamps for my pod filter? I could then seal the pod filter to the inside of the front wall of the air box with silicon so the only way for air to get in would be through the air box lid, which is right under the seat.

Then I would be using the air box (with modified lid) as a consistent volume of cool air pulled from right underneath the seat instead of sucking hot air from right next to the engine. I would still get the high flow of the pod filter, but hopefully with smooth cool air from the air box.

You think that would be the best of both worlds? Basically all I'm looking to do is use the pod filter inside the air box instead of on its own.

EDIT: I think this would really give me more consistent incoming air temps and smoother air while moving. Looking at some of my data from my EFI logging shows me that my incoming air temp really varies with the engine temp (and if I'm idling for any period of time like at a light)

Last futzed with by choneofakind; February 17th, 2013 at 03:50 PM.
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Old February 17th, 2013, 01:47 PM   #6
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Have you seen this one? Resonant Airboxes: Theory and Applications
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3 out of 3 members found this post helpful.
Old February 17th, 2013, 02:20 PM   #7
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Nice link Blue. Good read.
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Old March 13th, 2013, 08:48 AM   #8
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Indeed. Twas a good read.
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