Technical What does the air induction housing actually do?

[smart51]

The air filter housing has a very long induction pipe with a tiny inlet port. There are lots of small holes here and there, then a long hose to the carburettor. What is all this for? Normally, elaborate induction systems are either to reduce noise or to pulse tune the inlet for better breathing in a particular RPM band. The 500 isn't quiet, nor does it seem to breathe well. What is the reason for such a convoluted air intake?

 

[smart51]

The inlet is only about 10mm x 20mm. That has got to be a restriction.

 

[Bounding Bambino]

My understanding of this setup is multi fold, however, IIRC the main jist that i understood its funky design was to help prevent "back flow" fuel spit/mist going upstream. And in theory the air pressure from the fan inside the blower housing helped keep mild back pressure against the stock style carb to help prevent fuel from flowing upstream the intake tube. Especially since its at a slight downward angle.
If anyone had a vintage 2 stroke, especially a old skidoo from my neck of the woods, the engines would constantly spit and barf fuel out of the carbs onto the driver, something like this internal to the air cooling system would help keep backwash at bay.

I might be way off, but i believe that was the design ideal behind this system. The "simple style" factory carbs can spit and sputter fuel backwards at specific resonations/rpm

 

[bugsymike]

May be unrelated but we used to get "fuel stand off" on racing Karts back in the late 1960s at certain revs and a longer bell mouth to the carb improved things.
A longer inlet tract helped give more tractability/torque over a wider rev range on some circuits and if we needed a quicker throttle response a shorter inlet tract was used.
Obviously these were tuned two strokes so slightly different.
Factory air cleaner systems are designed to reduce the sound and provide a good air flow under a variety of conditions and temperatures.
Boy racers often fit pancake air filters and wonder why the car sounds "sporty" but spits back and doesn't go as well as before with original setup. They are allowing more air flow but the carb or fuel system hasn't been adjusted to match it. Plus the original set up was designed to get cooler clean air, far away from the engine. Hot and dirty fumey air has less oxygen in it, so less power.
The skidoo was a high performance two stroke in those days with port timing fairly extreme hence the "fuel stand off", much the same as Motocross bikes of the time, bags of power but a "bit of an animal", still great fun.

 

[vitorio]

Hmm, i wasnt aware that the channel between the cooling fan and the intake tract was so restrictive. The positive pressure from the fan might compensate, but going from a 615 mm^2 carb (28mm diameter circle, 452mm^2 for a 24) to a 200mm^2 opening is still going to choke things off. Not to mention the turbulence caused by the weird plate opening at the front of that channel.

Ive considered fitting one of those intake trumpets on the carb, but the lesser filtration and it sucking in hot air from the engine bay held me back.

Might put my newly acquired die-grinder to use and open up that hole a bit more, at least get it to the point where the channel itself is the restriction, not the front plate.

 

[bugsymike]

If you are referring to the oval hole at bottom of photo it looks like a steel plate pressed into the base and crimped over so it may be possible to ease the crimps and remove the oval plate, then if it gives a negative result it may be replaced.

 

[Goldnrust]

It's worth considering that removing any restrictions in the intake, or especially switching to an open filter / intake trumpet, is likely to upset the jetting in the carb. The carb will have been set-up to work with the restricted air flow offered by the intake and could well run lean without it. So to see any improvement you'll likely need to get the carb setup to match your new intake.

 

[The Panda Nut]

It always suprises me how people want to undo the work of the development engineers.
If you are going racing then you want to change the engine charcteristics, and probably the engine maps too and I can see the point.
On a road car the ECU is mapped to behave its miserable self with the original equipment in place, and as you largely cant fiddle with the map its almost certain that you will have worse emissions for messing with it, and almost definitely more noise, The air flow is messed with to produce the best compromise for road use and for certifications. The equipment is designed to ensure the air is filtered and available at the right place, pressure and time. It is also tuned for sound and to avoid resonance. ECU's read athmospheric pressure so it must be important to keep within the preset limits for best operation.

I understand the desire to tweak and fiddle but persoanally I think the current day resitrictionson whats going to improve things are removal of rough edges and burrs on the pipes and more importantly immaculate service records. The cost of even a secon hand air box are eye watering these days and I would be frightened of wrecking one.

It would be fun to see rolling road outputs on some of the minor mods which are done so often and see which have effects, both bad and good.

One of the reasons I loved the Panda 100 so much was that it ws beautifully quiet and refined and when driven off sounded reaaly smooth, while being able to scare the socks of all manner of bigger cars if pushed hard. Noise just attracts the wrong kind of attention!

 

[bugsymike]

"Factory air cleaner systems are designed to reduce the sound and provide a good air flow under a variety of conditions and temperatures."
As a youngster many years ago most of my vehicles were modified with "sportier exhausts" and other things, that plus my driving habits at the time meant attracting the attentions of the boys in blue. As I matured? I realised a quiet powerful car could be fun also.

 

[smart51]

It always suprises me how people want to undo the work of the development engineers.

Former development engineer here. Just because something was designed by a professional, it doesn't mean it is the best it could be. Cheapest perhaps.

Engine components are designed to work at full load, with the cheapest fuel, in both death valley and a snowy mountain top. They're also designed to be reliable and fool proof. An air restriction like this will have its most effect at high revs and full throttle. It may be there to deliberately curtail engine power so it won't rev over 5000 RPM so drivers don't burst the engine.

Edit to say that it is fine to change parts that a professional has designed if you accept the new compromises it delivers. You can get more top end power if you want that sort of thing. You have to accept the risk of over revving the engine, accept that the car may struggle in some extreme geographical environments or may have to use higher octane fuel.