Topic: Yes, Another AIRBOX mod!

[Bru-tom]

Hey guys, im in two minds whether this mod of mine will work.

I dont want pods as im sure you all know why, and i made the other bracket to fit a cone filter, but it looks messy to me. So i started building this!

got the basic shape, then plasma cut the inner, also basic shape, its a pain in the arse to use 



after a quick file and also cut the outside lip that i will weld around the circumference of the plate



Found some SS mesh to stop the filter material from getting sucked in:



one two skip a few, DONE! i will be drilling 3mm holes in each corner to rivet to the plastic box, the nuts you see are to attach the cover which will also be a mesh.

 

excuse the welds, im tired and it was a pain to weld!



Now, i have some of this filter material:



im not sure if i shouldn't just use a sponge, or what? it is designed to filter the air, i dont have any specific micron values but its designed for automotive apps.

will this small filter mod not hamper the flow too much?

any idea?

many thanks

brutom

[Lostboy Steve]

Looks nice! Great idea. What filter are you thinking of using?

[Bru-tom]

well, the filter you see there. or a sponge type, depending what i can get my hands on...

[iron_worker]

Seems like a pretty small area to be drawing through. You may find it ends up giving you more restriction. You'll know if your bike starts running very rich.

IW

[dave500]

good fabrication,im with iron worker though,that square mesh looks quite restrictive?

[Bankerdanny]

Nice job.

You might consider chicken wire rather than the grating you have in there now. It will hold your your filter media just fine while not restricting airflow at all.

[mono]

i like it - and i would use foam (personal preference, seems like it'd be easier too)

and i don't see it as being any more restrictive than the stock, since the stock filter is in an effectively airtight plastic housing which breathes from an even smaller vent under the seat, right  (seriously, correct me if i'm wrong here) ?  i think your draw will be greater.

[TwoTired]

Measure each of the mesh opening sizes length and width.  Multiply those numbers for cross section area of each rectangle.  Then count the rectangles and multiply the area by the number of openings that are present.
This gives you total inlet area.  Compare that to the stock inlet area of the filter box. 

The CB550 F models have a 4.5" x 1.5" inlet area. Area = 6.75 sq inches
The Cb500 (74-76 K models should be the same) I just measured is about 5" x 1.5".  Area = 7.5 sq inches.

You'd want your air plenum screen to measure at least what the filter box inlet area.  Further, those square inlet edges introduce turbulence closer to the carb inlets than does the stock filter.  The eddys from this, become physically longer as air speed increases, which increase restriction exponentially, if I recall correctly.

Filter media.
The stock filter media consists of 18 or 36 sides of pleats about .75 x 2.5" in size.  The area of each of the 36 sides is 1.875 sq inches, and 36 of them make a membrane 67.5 square inches in area.  If you chose a pleated material, I'd try for that area to replicate.
The unknown variable here is the permeability of the selected filter membrane.  This can vary among paper pleat types and certainly with the various foam filter types available.

A membrane more permeable can have a total are size smaller than the stock paper type and still yield the same pressure drop across it for the same rates of flow.  Generally, this also means that larger individual particles are allowed to pass through it, if that is of any concern to you.

Note that the stock set up had about nine times the filter area than the inlet area (not the same as air passage area, as the filter fibers are part of the membrane area measurement.).  This airflow area does reduce as it collects dirt though, as that is the function of the filter, and dirt can block inlet passageways.

Do understand that you are still shortening the inlet duct (from that of the air filter entrance  and this brings atmospheric pressure closer to the carb jets.  Thus, the jet outlets receive a pressure closer to atmospheric than the lower pressure the engine creates.  They will therefore provide less volume of fuel for the air entering the cylinders.  I've not quantified this, but you may have to alter jets sizes to restore the factory ratios.  Such is the way of experimentation.

You should be able to figure out what you want to do from this.

[Bru-tom]

thank you all! TT, thank you for the detailed explanation. i have since removed a few ribs in that square "grating". before its area measured 2950mm squared, now it measures 4200mm squared. the stock as TT mentioned is 4300mm squared. so its a little lower than stock.

i have since found some ss 10x10mm mesh:



should i rebuild the entire thing using it?

As TT mentioned, wont the squareness cause turbulence? or way less compared to the previous material used?

thanks for everyones input

[TwoTired]

Round wire is better than sharp edges, particularly at low speed.  However, realize that anything in the air flow path presents an obstruction, and increasing turbulence as the air speed increases.

Ever see a flag on a pole in the wind?  Notice how the flag undulates down wind of the pole?  Those are air current eddies that occur on the lee side of the flag pole.  The size of the eddy swirls change in width with the airspeed.  But, they never go away as long as the air is moving past the obstruction.

[Bru-tom]

Thanks TwoTired i fully understand what you are talking about.

this is what i have basically done to the original:



I am trying to get the best possible out of my air intake system without using the large stock system. I know that it will never be perfect, but i hope to get it operational as best i can. I thank you for all your advice.

If you look at the pic i posted above, i could get rid of more squareness by removing the centre cross member too, therefore only having vertical lines. that would be even better, not? more so than the mesh?

[TwoTired]

You should plan ahead and select the filter material, as pleated paper will be easier to hold in place than foam and require a bit less restraint.  I recommend you smooth out all those nubs, at least.  Anything in the air path is better off feeling like a used bar of soap.

[Bru-tom]

thanks mate!

i posted a picture of the pleated filter material in my first post. its a 10x10. not sure of micron filtration though.

That pic was one i did in MS paint to illustrate what i did. here is the actual pic of the piece...



im not sure now if i should even bother redoing it and replacing it with mesh instead?

rather leave it be as is, maybe remove the last few vertical segments?

[Bankerdanny]

At this point I would add the filter, install and see how it works.