Author Topic: i have an air filter idea (clarification update 3-14)  (Read 3290 times)

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Offline andy8190

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i have an air filter idea (clarification update 3-14)
« on: March 13, 2012, 08:45:53 PM »
Okay so I know some people go to the cone air filters but I want to make things more neat. I was thinking about buying some kind of air filter then using just the foam to cover up the hole in my stock air box on my 350f. Do you think this setup would work? what might be some issues. This way I still use the stock air box but not the filter and still use the stock boots.
« Last Edit: March 14, 2012, 10:07:08 AM by andy8190 »

Offline dave500

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Re: i have an air filter idea
« Reply #1 on: March 13, 2012, 08:47:41 PM »
probably start running lean.

Offline andy8190

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Re: i have an air filter idea
« Reply #2 on: March 13, 2012, 08:49:51 PM »
can you give me some reasons to why you think this? seems like it would be a similar setup to stock except not use the stock filter. If you want to decrease the air coming in can I just decrease the area of the opening?

thinking of using this http://www.motorcycle-superstore.com/2/9/427/32164/ITEM/Uni-Air-Filter-Bulk-Filter-Foam.aspx

Offline dave500

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Re: i have an air filter idea
« Reply #3 on: March 13, 2012, 09:15:22 PM »
unless it has the same sort of resistance as the stock paper filter itll probably run leaner,if it has more itll run richer.ive done this on a 500.a soft flame melted all the glue keeping the cage together,i reassembled it with good two part glue,then used finer filter brand foam.

« Last Edit: March 13, 2012, 09:21:23 PM by dave500 »

Offline andy8190

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Re: i have an air filter idea
« Reply #4 on: March 13, 2012, 09:23:38 PM »
yeah i wasnt even gonna go this far i was just gonna use the filter foam to cover up the inlet hole of the actual air chamber

Offline dave500

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Re: i have an air filter idea
« Reply #5 on: March 13, 2012, 09:25:58 PM »
i think just covering the hole will not filter enough.

Offline phil71

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Re: i have an air filter idea
« Reply #6 on: March 13, 2012, 09:26:47 PM »
an engine is an air pump. It takes air in, and fuel,  then shoves air out (with some nasty stuff). If you make it easier to get air in you have to give it proportionately more fuel to go with it. If you make it easier to push air out, you also need more fuel. Since you don't have the tools to measure what your super special homemade airbox is doing differently than the stock setup, you're going to have to dick with it. If you don't want to dick with it, leave it alone.

Offline flybox1

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Re: i have an air filter idea
« Reply #7 on: March 13, 2012, 09:45:35 PM »
why not just buy a new air filter to go in your stock air box, and save yourself the time and money trying to either A - rejet for your lean/rich depending on what foam you choose) condition, or
B - decrease the intake area perfectly to exactly match the given fuel supply from the jets you have in there.

why mess with something well engineered?

$30 bucks and you're riding....
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Offline dave500

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Re: i have an air filter idea
« Reply #8 on: March 14, 2012, 01:16:49 AM »
i think flybox has a pretty good idea.

Offline Deltarider

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Re: i have an air filter idea
« Reply #9 on: March 14, 2012, 01:38:38 AM »
Quote
why not just buy a new air filter to go in your stock air box, and save yourself the time and money trying to either A - rejet for your lean/rich depending on what foam you choose) condition, or
B - decrease the intake area perfectly to exactly match the given fuel supply from the jets you have in there.

why mess with something well engineered?

$30 bucks and you're riding....

+1
To renew my airfilter element it will take me 10 seconds max!
This includes: insert key in seatlock, open the seat, remove tool tray, remove cover, remove retaining clip, pull out the old element and vice versa.
Further advantages: best filter medium available, never have to worry about anything.
Bonus: You'll contribute to maintain demand for Honda Genuine Parts and that's a good strategy for the long run.
« Last Edit: March 14, 2012, 01:41:46 AM by Deltarider »
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Offline Terry in Australia

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Re: i have an air filter idea
« Reply #10 on: March 14, 2012, 01:51:19 AM »
Do you mean just covering the air inlet hole in your airbox with foam mate? 350F's are great little bikes but with 32 BHP (at the crank) they're not overly endowed with power, so I'm guessing that you're trying to put a little more pep in your step? Heffay put pods on his 350F and after playing with the jetting, he got a pretty good result.

My advice (FWIW) would be to either try to find a freer flowing filter (K&N?) for your airbox, or go the pods route. Either way, you'll need to play with the jetting. Cheers, Terry. ;D
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Offline TwoTired

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Re: i have an air filter idea
« Reply #11 on: March 14, 2012, 02:07:14 AM »
Okay so I know some people go to the cone air filters but I want to make things more neat. I was thinking about buying some kind of air filter then using just the foam to cover up the hole in my stock air box on my 350f. Do you think this setup would work? what might be some issues. This way I still use the stock air box but not the filter and still use the stock boots.

Are you thinking of something as depicted below?
Lloyd... (SOHC4 #11 Original Mail List)
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Offline faux fiddy

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Re: i have an air filter idea
« Reply #12 on: March 14, 2012, 03:13:38 AM »
Okay so I know some people go to the cone air filters but I want to make things more neat. I was thinking about buying some kind of air filter then using just the foam to cover up the hole in my stock air box on my 350f. Do you think this setup would work? what might be some issues. This way I still use the stock air box but not the filter and still use the stock boots.

Are you thinking of something as depicted below?

There was a plenum for sale on e-bay with a setup like this. It didn't have the filter with it but the oval was replaced with a plate and standard (ish) size round fitting for a K$N or foam filter.
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Offline jessezm

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Re: i have an air filter idea
« Reply #13 on: March 14, 2012, 06:07:58 AM »
Can you provide a link to this?

Offline flybox1

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Re: i have an air filter idea
« Reply #14 on: March 14, 2012, 08:05:20 AM »
Okay so I know some people go to the cone air filters but I want to make things more neat. I was thinking about buying some kind of air filter then using just the foam to cover up the hole in my stock air box on my 350f. Do you think this setup would work? what might be some issues. This way I still use the stock air box but not the filter and still use the stock boots.

Are you thinking of something as depicted below?

TT, I think he was going to plug the inlet hole under the seat with foam....
 
As he's described it, he'll be using the stock airbox.  from the outside of the bike, nothing has changed.  is he trying to cut corners and save a few bucks, or trying to get more out of this little 4.
I cant see how this makes it more 'neat'. you're either servicing a paper element, or the foam you crammed in. not to mention the change in AF mix.  re-jetting may be required. 
I think he needs to define "neat".   :)
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Offline Duke McDukiedook

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Re: i have an air filter idea
« Reply #15 on: March 14, 2012, 08:27:01 AM »
Just stuff some dirty old socks in there, it will give about the same effect.
Filter!?!?! Phushaw...  ::)
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Offline FrankenFrankenstuff

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Re: i have an air filter idea
« Reply #16 on: March 14, 2012, 09:22:09 AM »
I like the K&N option. I am going to make one for myself....is anyone else interested?

Offline andy8190

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Re: i have an air filter idea (clarification update)
« Reply #17 on: March 14, 2012, 10:06:43 AM »
guys just to clarify I do not want to use the stock airbox I just want to keep part number 15 below



TwoTired yes I was thinking of using a setup like that or just making a flat one that fits over the inlet hole to the part above. I cut up my triangle where the stock airbox would attach to so I have to come up with another option. Here is my set up of the triangle are


Offline flybox1

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'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

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Offline TwoTired

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Re: i have an air filter idea (clarification update 3-14)
« Reply #19 on: March 14, 2012, 12:03:54 PM »
Across any filter media, there exists a pressure drop from one side to the other, because the filter media cause the direction of air flow the change and or turbulate.
The magnitude of the pressure drop relates to the speed of the air moving through it as well as how dense the filter media is and the shape of the fibers doing the filtering.

You'll note that the stock filter media is pleated.  This is not just for cool looks.  If you removed the paper and stretched it out accordion style, you'll find there is a lot of media there packed into a small space, far more than if the media was just stretched around the outside shape of the filter.
This is done to lower the air speed moving across any section of filter.  A given volume of air moving through a small area must move faster than the same volume of air through a larger cross section of area.  Generally speaking, faster air creates more turbulence around a pathway obstacle.

The paper type filter has a very large number of small pathways, so that the air speed through each pathway can be kept low and suffer from fewer air turbulence, speed robbing effects.

You CAN find alternate filter membranes that have larger pathways through it and make the overall filter media size footprint smaller and still have nearly the same pressure drop characteristics.  But, it doesn't come about with just casual visual inspection.  Therefore, it is generally accepted that if you change the filter media type and or size, you WILL change the pressure drop across the membrane.

The pressure drop factor is important as all the fuel jets react to the pressures inside the carb throat to change the flow rate of the fuel entering the carb throats.  And, the filter membrane is one of the barriers for outside air pressure to reach into the carb throat.  Remember, it is the outside pressure that pushes the fuel through the fuel jet into the lower pressure of the carb throat.  You may have observed that the fuel jet supplies no fuel into the carb throat when the pistons aren't moving in the cylinders and that is because the pressure inside the carb throat is equal to the outside air pressure, so no fuel movement is possible.

The jet sizes/adjustments in the carb was selected by engineers/mechanics for the particular characteristic pressure drop the stock filter provided, and there is no mechanism in engine or carb to automatically alter the fuel jet metering parameters in response to a filter media pressure drop change.

Your question:
Okay so I know some people go to the cone air filters but I want to make things more neat. I was thinking about buying some kind of air filter then using just the foam to cover up the hole in my stock air box on my 350f. Do you think this setup would work?
A qualified yes.  Assuming you wish to also change the pilot jetting, the main jetting, the slide or throttle valve jetting, and possibly the slide cutaway angle.
Also note that with decreased filter area high speed pressure drop effects are more severe and begin to reduce that actual volume that can be delivered to the engine.  Reduced volume means less oxygen getting to the cylinders, and reduced resultant power, (even if you do readjust the A/F ratio to ideal.)   So, it may seem to work out ok for idle and even some mid-range speeds, but you can easily lose power up around red line RPMs.  Of course, that won't effect how it looks in the garage or in parking lots or pictures where people can ogle your bike and say, "neat".

what might be some issues.

I think this was covered...

Cheers,
Lloyd... (SOHC4 #11 Original Mail List)
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Offline andy8190

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Re: i have an air filter idea (clarification update 3-14)
« Reply #20 on: March 14, 2012, 11:47:21 PM »
okay lets say i keep the original set up in the picture above, do i really need part number 7 because I wont have a hole for it to fit in under my seat anyways and even if I did I am running a fiberglass seat so will be hardly no air flow into it?

Offline TwoTired

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Re: i have an air filter idea (clarification update 3-14)
« Reply #21 on: March 15, 2012, 03:11:18 AM »
Technically you should have it, assuming you are not wanting to rejet/adjust the carbs, as it is part of the entire duct.  See:
http://forums.sohc4.net/index.php?topic=83904.msg945765#msg945765
Practically, it's probably ok to not have it, and will only lean the mixtures slightly.  How long is # 7,  6-7 inches?  What is the distance between the filter box inlet and the intake valve in the head?
I will ask if there is going to be a rear fender to keep the tire from throwing mud, dirt, water, oil droppings, and grease picked up from the road at the filter box opening to be sucked in.
Lloyd... (SOHC4 #11 Original Mail List)
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