help me understand twin filtered air box design?

[Lazy7]

Hey guys,

i replaced the filter in my bike with a k&n item, and when i did it, i couldn't help wonder what the hell the designers were doing when they designed the air box?

for some reason, the air gets passed through the filter twice.

i have drawn a small diagram (excuse the ranginess) to show you what i mean.

the air comes in from the left, through the ram air, through the filter - up into the top of the air box, over the ridge in the base, then back down through the filter again into the trumpets.

my question - if you have a good air filter - why does it need to be filtered twice. wouldn't the second filter be just added flow resistance?

can i chop the second half (back half, smaller half off)

have attached an actual picture of the filter so you know what i mean.

[White trash]

Well you'd need to rejet obviously but I guess you've done this with the K&N anyway. The horible filtration theories I've heard from a number of K&N knockers though, is that you're probably lucky it passes through the filter twice.

And with the millions spent developing the bike, I'm pretty sure the designers had an idea of what they were doing.

[Sniper]

There may be that fraction more resistance in airflow, but I seriously doubt that you will notice any difference by copping it in half. Personally I like the idea of air being filtered twice. Double protection against nasty airborne shit that can damage or clog up the motor.

[onearmedbandit]

Yeah, as WT says I'd be pretty sure they know the WHOLE picture when designing your bike. However, there can be reasons to do with compromise (ie economy, noise testing) that hinder performance. Only one way to find out.

[Ixion]

If the air filter and air box are of sufficient size, then any restriction they present is irrelevant . For example if the filter imposed such a restriction that the air volume passing through it was reduced by half (in reality, far less of course), BUT the filter had twice the area of the carb mouths then the extra ara compensated for the restriction . This is why there is an air box on the filtered side. (It's more complicated than that, because of velocities and such, real life is always more complicated, but you get the idea)

Extreme example. suppose you put a bike into a huge room, with the exhaust taken to outside, and all the air coming into the room filtered through huge filters. Now, in that event you wouldn't need an air filter on the bike (simplistic of course, because you still have the rider shedding particles etc). But you would not have any loss of power due to restriction, even though the air is filtered.

[Motu]

Looks like a pretty sensable design,making maximum use of a small space...that's not a lot of filter area,so they doubled it up.The K&N is not a good idea though - hold it up to a good light and see all the holes,maximum air flow,minimum filtering.

[Mental Trousers]

Just guessing here but I'd say the first filter it passes through is coarser than the 2nd part, so the first one takes out large stuff while the 2nd filters out smaller stuff.

Also, it's a ramair design. If there weren't any filters there you'd end up with different pressures in different parts of the airbox, leading to different amounts of air going to each cylinder etc. So having 2 filters there helps to eliminate fluctuations throughout the airbox.

[WINJA]

Looks like a pretty sensable design,making maximum use of a small space...that's not a lot of filter area,so they doubled it up.The K&N is not a good idea though - hold it up to a good light and see all the holes,maximum air flow,minimum filtering.

ID GO WITH YOUR MINIMUM FILTERING THEORY EVERY TIME , BUT ITS A FACT THAT THE LATE MODEL GIXXER PAPER FILTERS FLOW MORE THAN ANY K AND N EVER COULD , ITS ABOUT SURFACE AREA JUST LOOK AT THE AMOUNT OF PLEATS

[WINJA]

Hey guys,

i replaced the filter in my bike with a k&n item, and when i did it, i couldn't help wonder what the hell the designers were doing when they designed the air box?

for some reason, the air gets passed through the filter twice.

i have drawn a small diagram (excuse the ranginess) to show you what i mean.

the air comes in from the left, through the ram air, through the filter - up into the top of the air box, over the ridge in the base, then back down through the filter again into the trumpets.

my question - if you have a good air filter - why does it need to be filtered twice. wouldn't the second filter be just added flow resistance?

can i chop the second half (back half, smaller half off)

have attached an actual picture of the filter so you know what i mean.

STOP JUST THINKING OF IT AS AN AIRFILTER , HAVE YOU EVER FELT A CARB SPIT BACKWARDS AT CERTAIN REVS , WHAT IF THAT SPIT COULD BE HARNESSED WITH A SMALL AMOUNT OF RESISTANCE TO HELP PRECHARGE THE NEXT CYLINDER ON THE INTAKE STROKE , THERE COULD BE MORE TO IT BEYOND K AND N'S COMPREHENSION.
KAWASAKI ARE THE MASTERS OF RAM AIR ,THEY PIONERED THE FIRST BIKE TO BE SOURCED FROM A HIGH PREASURE AREA THAT WAS THE GPZ1000RX,I WOULDA LEFT THE SAME FILTER IN , CAUSE YOU WANNA KNOW THE TRUTH SEE THOSE OLD ZX7 RACE BIKES IN AMA AND WSB WITH K AND N OR BMC STICKERS ON THEM THEY HAD NO FUCKEN FILTERS IN THEM