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Pod filter trick. Can it be done?

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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When going to pods I've heard that you have to rejet. Has anyone tried to restrict the flow of the pod filters to reduce the air flow so that rejetting is not needed. I would think you could do something to reduce air flow of the filter and this might be easier and cheaper than rejetting. Just tell me if I'm thinking with my arse. :)
 
I think you can match the flow and vacuum for only a portion of the rev range, and most probably not the lower ranges where response will suffer.
 
ummmm... if you're just going to restrict the flow again, whats the point? :?:
 
spots25 said:
ummmm... if you're just going to restrict the flow again, whats the point? :?:
Click to expand...

I posed that question not too long ago on another thread, as far as why hasn't anyone tried to match pods airfloe to the stock airbox. My reason was to get rid of that danged air box. So it was more for convenience of working on the machine that increased performance and spending all the money to get that perfomance.
 
ummmm... if you're just going to restrict the flow again, whats the point?
Click to expand...

Airboxes are a pain in the a$$. Unfortunately, they work. Like a charm too. Damn engineers did thier homework.

I'd be willing to bet that there is more to the whole airflow thing than most of us think of. Recently I got into a discussion with someone (can't remember who, long time member) that questioned why there was more more airflow at all with pods, that the stock airbox should flow as well as pods. At first I explained that the airbox ports must be smaller than the carb throats. After some debate I finally measured the ports on my airbox. There are two holes of almost exactly the same size as the carb throats in the air box. The air filter itself in a stock airbox is huge, so that can't restrict much flow, and as only two carbs are sucking at a time, this would seem like an unrestricted setup! I'm not smart enough to argue that further.

There has to be more to it. Maybe there is some delay in getting the air from the ports to the carbs? Maybe there is some kind of vortex or cosmic voodoo that only the Japanese know of?

If someone can explain- what say you??
 
After some debate I finally measured the ports on my airbox. There are two holes of almost exactly the same size as the carb throats in the air box. The air filter itself in a stock airbox is huge, so that can't restrict much flow, and as only two carbs are sucking at a time, this would seem like an unrestricted setup!
Click to expand...

That would seem to be the case, but is not in reality. There is a global flow that the airbox must handle and it is NOT two carbs at once, it s the total volume of air the engine is putting through. My 1100E will flow somewhere around 170 ft^3/min of air at redline (assuming a volumetric efficiency of 100%, which is not far off). If you draw that air through two 2" diameter ports, that gives a velocity of about 65 ft/sec. More than fast enough to generate significant flow losses. When you force the flow to follow a convoluted path, it causes flow resistance. Which causes pressure drops. Which cause low charge density and less power. Pods simply offer less restriction and lower pressure drops, which lead to more power. Don't assume that the OEM pleated paper filter is not a restriction just because it is big. That style of filter offers a lot of flow resistance. That is why adding a K&N filter in the box can add some power - it offers lower flow resistance. The paper element type get plugged very easily (even a small amount of trapped dust can seriously reduce the flow) and that again causes less power.

Pods may also cause less desireable effects on low end and midrange power/response and mess up smooth running due to the much smaller intake volume in front of the carbs, but that is not a guarantee either way, good or bad.

Properly designed, an airbox will make more power with smoother response than pods, but our old bikes don't really fit into that category. The bike OEM's didn't start spending a lot of effort on designing really good airboxes until government regs forced them to. The latest ones are fantastic, but you cannot TOUCH them or you will lose power. And how much fun is that? :)


Mark
 
The answer to this is CFM's that can be flowed, and the difference is big. The size of the airbox doesn't matter, it's the size of the hole supplying the airbox that matters. In my case the outlet from the filter is approx. 2.25", which gives an area of 3.976 in.sq. that supplies ALL the carbs.

Each pod outlet is approx. 2.1" which means 3.464in.sq. to EACH carb or a total of 13.854in.sq. to all carbs.

You can do the same math for surface area of the filter material in each case and let's not forget that the material (in K&N's case) flows better than stock material. Obviously the stock carbs can flow alot more air than the airbox is capable of.
 
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