K&N pod filters...

devlin · Post by **devlin** » Thu Nov 15, 2007 1:26 pm

Wouldn't pod filters create still air as the air passes through the filter? Once it is inside the filter would it not be laminar as it flows down the throat of the carby. Just trying to understand the physics of what is happening to the air. My thinking assumes the main idea of pod filters is to increase filter surface area to create more air flow. I can see this happening if they were still inside the air box where the air flow would be more laminar to the pods. Has anyone ever tried ram air into the inlet side of the air box?

Post by **phuk72** » Thu Nov 15, 2007 1:40 pm

How an airbox works is surprisingly complicated - it is not just a box full of static air. Ever wondered why they are so big? Ever thought about volumetric efficieny and pressurised units?

Seriously, the physics behind them is mind boggling!

Also, proper ram air is not just a matter of flowing air into the airbox via a big tube. To achieve decent results is complicated and expensive.

devlin · Post by **devlin** » Fri Nov 16, 2007 8:45 am

Yes I certainly won't pretend to understnad. I think i'll have to do some research as I am now intrigued.

devlin · Post by **devlin** » Sat Nov 17, 2007 12:08 pm

Here is a good article that helps understand what an airbox does.

http://www.calsci.com/motorcycleinfo/Airboxes.html

Now can someone tell me why the FCR's run with out one?

Post by **phuk72** » Sat Nov 17, 2007 2:32 pm

To understand that you'll need to understand the differences in CV carbs and FCRs.

Probably best to google as I'll only confuse the issue

devlin · Post by **devlin** » Sun Nov 18, 2007 12:47 pm

Cheers. I'll do some more research. It is actually very interesting reading.

Quan-Time · Post by **Quan-Time** » Mon Nov 19, 2007 2:37 am

the best airbox is the biggest one possible. Thats what the ferrari F1 team found, you can also have velocity stack inside an airbox if needed (such as changing carbs)

Carbies work on a "venturi" effect.. Get a cup of water, put a straw inside the cup, and one outside, now suck. This is "pressure difference effect". (incidentally you can make a "manometer" like this, and make a home made flow bench)

The ratio in which fuel is mixed with air depends on the air velocity thru carbie, NOT the amount of air.. If you put a too big a carb on an engine, you LOOSE efficency, as the air required to make the carb function properly is not achieved.
Airboxes will slow down the velocity of air going into a carbie, unless you have another effect on it, such as a funnel.

As stated previously, the maths / physics is HUGE in this area.

ALso note than many GP / SBK bikes now run the whole duck tail as the airbox to increase static volume.

youngy · Post by **youngy** » Mon Nov 19, 2007 7:56 am

They also run pressurised systems and have a lot of clever elctrickery to handle the fuelling.

Post by **phuk72** » Mon Nov 19, 2007 8:58 am

All of the above is very true.

Now who wants to explain why FCRs work so well with pod filters then

devlin · Post by **devlin** » Mon Nov 19, 2007 9:47 am

Because you don't need a vacuum to open the slide as it's done via the throttle? I'm having a stab at that without doing any further research or knowing how the FCR's work.