BMW K bikes (Bricks)

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1Back to top Go down   The Air Box?? Empty The Air Box?? on Sun Nov 11, 2018 6:24 am

DBRMN

DBRMN
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I was just curious what the different components of the Air Box do, and why there's two different sections. I also know that within the throttle body air box there are individual trumpets. Does this mean putting open trumpets on would be simple, or would that involve extensive modification? Basically if someone could just explain the Air box in depth and the effects of modifying or editing parts of it.

For example what is the point of the open trumpets here, besides looking cool and how is it interacting with the air box system.
The Air Box?? 61bcd510

Thanks
DBRMN

    

2Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Sun Nov 11, 2018 8:30 am

Dai

Dai
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Looking cool is all they're doing. I was instantly suspicious when I saw the plenum chamber, so I dumped the picture into PhotoShop and blew it up - sure enough, the airflow meter has been moved round and plugged into the back of the plenum chamber. No attempt to disguise it Rolling Eyes 

Because of the interplay between the airbox, the AFM, the FICU and the plenum chamber, it is just about impossible to modify the air intake system on a 2-valve K. It's a whole different ballgame on the 4-valve engine where there is no AFM. Motorbike Mike on here tried fitting a 4-valve FICU to a 2-valve engine and disposing of the AFM (yes, it needed a new wiring loom too) but found the the engine was wildly overfueling at times.

In short, the only modification you can do is to dispose of the airbox and to plug the AFM directly into the plenum chamber. You'll then need an air filter on the intake side of the AFM. What that does to the engine response I don't know, but I doubt it's good because by removing the airbox, you've removed a huge reservoir of air ready for the engine for the times when the intake airflow is disturbed.


__________________________________________________
'83 K100 upgraded to K100RS spec
Others...
'78 Moto Guzzi 850-T3, '79 Moto Guzzi 850-T3 California,'93 Moto Guzzi 1100ie California,
'03 Suzuki Blandit GSF600SK3 (NFS any more because wifey has claimed it)
    

3Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Sun Nov 11, 2018 8:36 am

DBRMN

DBRMN
Life time member
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@Dai wrote:Looking cool is all they're doing. I was instantly suspicious when I saw the plenum chamber, so I dumped the picture into PhotoShop and blew it up - sure enough, the airflow meter has been moved round and plugged into the back of the plenum chamber. No attempt to disguise it Rolling Eyes 

Because of the interplay between the airbox, the AFM, the FICU and the plenum chamber, it is just about impossible to modify the air intake system on a 2-valve K. It's a whole different ballgame on the 4-valve engine where there is no AFM. Motorbike Mike on here tried fitting a 4-valve FICU to a 2-valve engine and disposing of the AFM (yes, it needed a new wiring loom too) but found the the engine was wildly overfueling at times.

In short, the only modification you can do is to dispose of the airbox and to plug the AFM directly into the plenum chamber. You'll then need an air filter on the intake side of the AFM. What that does to the engine response I don't know, but I doubt it's good because by removing the airbox, you've removed a huge reservoir of air ready for the engine for the times when the intake airflow is disturbed.
So in short any modification is a bad idea. Can you explain the function of each section, for example what is the plenum chamber?

    

4Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Sun Nov 11, 2018 10:06 am

Dai

Dai
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Brief explanation, because I'm damned if I'm going into the thermodynamics of it! The Air Box?? 44271 

The air box takes air from the air intake and both filters it and acts as a very short term reservoir. From there, it goes through the AFM to the plenum chamber. The AFM does exactly that; it measures the air flow demanded by the engine and passes the data on to the FICU to determine how much fuel is needed. The plenum chamber acts as an equalising chamber for the four intake trumpets (venturi) because the cylinders pull air at different times. Each of those venturi acts as a restriction in the air flow which accelerates the air into the cylinder and jams more air in than would be possible without the venturi. Google 'venturi effect'.

Anyone got anything to add to that very, very brief description?


__________________________________________________
'83 K100 upgraded to K100RS spec
Others...
'78 Moto Guzzi 850-T3, '79 Moto Guzzi 850-T3 California,'93 Moto Guzzi 1100ie California,
'03 Suzuki Blandit GSF600SK3 (NFS any more because wifey has claimed it)
    

5Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Sun Nov 11, 2018 10:34 am

Laitch

Laitch
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@DBRMN wrote:For example what is the point of the open trumpets here, besides looking cool and how is it interacting with the air box system.
I think the only point of those open trumpets is decoration, similar to a 1953 Buick's Cruiserline Ventiports but with even less purpose.  Smile   The whole image looks like a concept illustration rather than a real moto. Do you have a link to it?


__________________________________________________
1995 K75 73,000 miles
The Air Box?? Usa-lo10
    

6Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Sun Nov 11, 2018 10:36 am

Point-Seven-five

Point-Seven-five
Life time member
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Good explanation, Dai. 

I would only add that requirements for a 100,000 mile service life on the air filter by the EPA dictated it's size and the size of the airbox below it.  The design criteria of the box is to allow uniform airflow across the entire surface area of the filter.


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

7Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Sun Nov 11, 2018 10:41 am

Point-Seven-five

Point-Seven-five
Life time member
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I just wanna know how they get them to keep from falling down when they're parked without a side or center stand.


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

8Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Sun Nov 11, 2018 10:43 am

Laitch

Laitch
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@Point-Seven-five wrote:I just wanna know how they get them to keep from falling down when they're parked without a side or center stand.
It has a gyroscope linked to pump-activated helium-filled stabilizer bags linked to storage tanks. The whole system is hell on battery life.


__________________________________________________
1995 K75 73,000 miles
The Air Box?? Usa-lo10
    

9Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Sun Nov 11, 2018 4:13 pm

DBRMN

DBRMN
Life time member
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@Dai wrote:Brief explanation, because I'm damned if I'm going into the thermodynamics of it! The Air Box?? 44271 

The air box takes air from the air intake and both filters it and acts as a very short term reservoir. From there, it goes through the AFM to the plenum chamber. The AFM does exactly that; it measures the air flow demanded by the engine and passes the data on to the FICU to determine how much fuel is needed. The plenum chamber acts as an equalising chamber for the four intake trumpets (venturi) because the cylinders pull air at different times. Each of those venturi acts as a restriction in the air flow which accelerates the air into the cylinder and jams more air in than would be possible without the venturi. Google 'venturi effect'.

Anyone got anything to add to that very, very brief description?
Wow I love this kind of stuff its amazing how complex just the air system can be, ye I'm definitely not going anywhere near that to modify it. Thank you so much this explained alot.

    

10Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Sun Nov 11, 2018 4:16 pm

DBRMN

DBRMN
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@Laitch wrote:
@DBRMN wrote:For example what is the point of the open trumpets here, besides looking cool and how is it interacting with the air box system.
I think the only point of those open trumpets is decoration, similar to a 1953 Buick's Cruiserline Ventiports but with even less purpose.  Smile   The whole image looks like a concept illustration rather than a real moto. Do you have a link to it?
This is a video about the bike but the original creators are from Brazil, its one of the bikes hat inspired me to chose the K100.

    

11Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Mon Nov 12, 2018 2:33 am

Laitch

Laitch
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@DBRMN wrote:This is a video about the bike but the original creators are from Brazil, its one of the bikes hat inspired me to chose the K100.
Thanks for the video link.

As soon as I heard the guy with the robo-voice that sounds like he's about to swoon in his excitement about this moto, I recalled having viewed it previously. I'd sure like to understand the function of those velocity stacks because, as Dai has observed, the engine still seems to have an air flow meter attached to it elsewhere.


__________________________________________________
1995 K75 73,000 miles
The Air Box?? Usa-lo10
    

12Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Mon Nov 12, 2018 11:51 am

DBRMN

DBRMN
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Found something really interesting, look at the video below at about 6:30, this guys completely gotten rid of the right hand side air box. What does everyone think of that, I think it's brilliant makes so much space for other stuff.

BTW this guy is doing a brilliant series on his K100 build finding it so useful.

    

13Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Mon Nov 12, 2018 2:14 pm

Dai

Dai
Life time member
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Seems to be a fairly common mod in the cafe racer crowd. Don't forget you'll now need some form of filter on the end of the AFM.


__________________________________________________
'83 K100 upgraded to K100RS spec
Others...
'78 Moto Guzzi 850-T3, '79 Moto Guzzi 850-T3 California,'93 Moto Guzzi 1100ie California,
'03 Suzuki Blandit GSF600SK3 (NFS any more because wifey has claimed it)
    

14Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Mon Nov 12, 2018 2:19 pm

DBRMN

DBRMN
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@Dai wrote:Seems to be a fairly common mod in the cafe racer crowd. Don't forget you'll now need some form of filter on the end of the AFM.
This is defo a mod I'm going to consider because it would provide space for ECU and ABS unit.
He he used this beautiful K&N Filter:

The Air Box?? Screen10
The Air Box?? Screen10

    

15Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Mon Nov 12, 2018 5:50 pm

Point-Seven-five

Point-Seven-five
Life time member
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@Dai wrote:Don't forget you'll now need some form of filter on the end of the AFM.

Just curious.   Why does a cafe racer need an air filter???


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

16Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Mon Nov 12, 2018 7:46 pm

RicK G

RicK G
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When you race a cafe it often wins and they do kick up a lot of dust


__________________________________________________
"Man sacrifices his health in order to make money.
Then he sacrifices money to recuperate his health.
And then he is so anxious about the future that he does not enjoy the present; the result being that he does not live in the present or the future; he lives as if he is never going to die, and then dies having never really lived."   Dalai Lama


Bikes 1993 K1100 LT, 1998 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 for now
    

17Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Mon Nov 12, 2018 7:49 pm

DBRMN

DBRMN
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I’m thinking of hiding my battery, ECU and ABA unit there will it be too hot? What about with heat sheilding and a gap?


__________________________________________________
https://www.gofundme.com/manage/helping-fund-my-motorbike-project
    

18Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Mon Nov 12, 2018 7:50 pm

DBRMN

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Rick G makes good points you wouldnt know the problem in your stock world 😂 lol


__________________________________________________
https://www.gofundme.com/manage/helping-fund-my-motorbike-project
    

19Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Mon Nov 12, 2018 7:56 pm

Point-Seven-five

Point-Seven-five
Life time member
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And the coffee grounds...Oh, the coffee grounds.  Cafes spew them everywhere.  It's the reason I avoid cafes.


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

20Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Mon Nov 12, 2018 8:33 pm

K75cster

K75cster
Life time member
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I've been thinking about those velocity stacks and I believe they are to allow you to still reach the big brass screws. I'm not big on Café racers but then again I have a preference to just sip coffee even when it's Loffee. Although I guess I can gulp down the last of it if they're all waiting on me.


__________________________________________________
Keith - 1987 K75c with r100rt replica fairing and half of a 1984 K100rt 1992 K1100LT a blue one

The Clever are adept at extricating themselves from situations that the wise would have avoided from the outset - QUOTE from david Hillel in Out of the Earth.
    

21Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Tue Nov 13, 2018 8:29 am

ERasberg

ERasberg
Silver member
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@Dai wrote:Brief explanation, because I'm damned if I'm going into the thermodynamics of it! The Air Box?? 44271 

The air box takes air from the air intake and both filters it and acts as a very short term reservoir. From there, it goes through the AFM to the plenum chamber. The AFM does exactly that; it measures the air flow demanded by the engine and passes the data on to the FICU to determine how much fuel is needed. The plenum chamber acts as an equalising chamber for the four intake trumpets (venturi) because the cylinders pull air at different times. Each of those venturi acts as a restriction in the air flow which accelerates the air into the cylinder and jams more air in than would be possible without the venturi. Google 'venturi effect'.

Anyone got anything to add to that very, very brief description?

@ Dai : Awesome explanation !


__________________________________________________
Present
1988 K100 RS SE - VIN# 0146971K100RS - 105,000 km
1998 R1200C
1971 R75/5

Previous
1999 Virago XV125
1981 R65
    

22Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Tue Nov 13, 2018 2:34 pm

charlie99

charlie99
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@Dai wrote:Brief explanation, because I'm damned if I'm going into the thermodynamics of it! The Air Box?? 44271 

The air box takes air from the air intake and both filters it and acts as a very short term reservoir. From there, it goes through the AFM to the plenum chamber. The AFM does exactly that; it measures the air flow demanded by the engine and passes the data on to the FICU to determine how much fuel is needed. The plenum chamber acts as an equalising chamber for the four intake trumpets (venturi) because the cylinders pull air at different times. Each of those venturi acts as a restriction in the air flow which accelerates the air into the cylinder and jams more air in than would be possible without the venturi. Google 'venturi effect'.

Anyone got anything to add to that very, very brief description?

yes ,
just to mention that the size and location of the air box (in the system ) reduces induction noise very markedly

a requirement to attempt to satisfy the noise regulations across all manufacturers ,  in some cars you will find a small box attached to the inlet path after the air cleaner ,. which is designed just for that reason , but other wise seems of little value , until you remove it and hear the change in induction noise, it is quite apparent .

the intake trumpets , commonly called velocity stacks are designed to affect the peak induction velocity at certain revs (as dai says , to do with cylinder filling ), and can often be designed to improve performance of the motor at the designed rev range expected , so enhances the whole system if designed correctly , like exhaust but in reverse

the length of the air induction system , from valve seat to air inlet snorkel opening can also enhance low end engine efficiency and torque,


__________________________________________________
cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%OThe Air Box?? Au-log10

"redframe" rs "bitsa"  with many contributions from the k100 community ,,with many thanks
    

23Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Tue Nov 13, 2018 8:03 pm

DBRMN

DBRMN
Life time member
Life time member
@charlie99 wrote:
@Dai wrote:Brief explanation, because I'm damned if I'm going into the thermodynamics of it! The Air Box?? 44271 

The air box takes air from the air intake and both filters it and acts as a very short term reservoir. From there, it goes through the AFM to the plenum chamber. The AFM does exactly that; it measures the air flow demanded by the engine and passes the data on to the FICU to determine how much fuel is needed. The plenum chamber acts as an equalising chamber for the four intake trumpets (venturi) because the cylinders pull air at different times. Each of those venturi acts as a restriction in the air flow which accelerates the air into the cylinder and jams more air in than would be possible without the venturi. Google 'venturi effect'.

Anyone got anything to add to that very, very brief description?

yes ,
just to mention that the size and location of the air box (in the system ) reduces induction noise very markedly

a requirement to attempt to satisfy the noise regulations across all manufacturers ,  in some cars you will find a small box attached to the inlet path after the air cleaner ,. which is designed just for that reason , but other wise seems of little value , until you remove it and hear the change in induction noise, it is quite apparent .

the intake trumpets , commonly called velocity stacks are designed to affect the peak induction velocity at certain revs (as dai says , to do with cylinder filling ), and can often be designed to improve performance of the motor at the designed rev range expected , so enhances the whole system if designed correctly , like exhaust but in reverse

the length of the air induction system , from valve seat to air inlet snorkel opening can also enhance low end engine efficiency and torque,
Wow so it could potentially be a very worthwhile upgrade, I'm assuming you'd  have to get it done by a specialist though. What kind of kit would you need? I don't even know what type of shop could do something like that

    

24Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Tue Nov 13, 2018 9:25 pm

charlie99

charlie99
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a couple of pockets of money , a dyno , and some good engineering and maths skills

as usual, I have none of the above .

these days an additional complexity , actually an advantage is the new modern programable ecu  to get the most out of it all


__________________________________________________
cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%OThe Air Box?? Au-log10

"redframe" rs "bitsa"  with many contributions from the k100 community ,,with many thanks
    

25Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Tue Nov 13, 2018 9:42 pm

jahearne

jahearne
active member
active member
BSK has some cool looking throttle bodies with stacks

http://www.bskspeedworks.co.uk/k-throttle-bodies.html

The Air Box?? K_bill10


__________________________________________________
The Air Box?? 1181537659 - John
    

26Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Tue Nov 13, 2018 10:05 pm

Laitch

Laitch
Life time member
Life time member
The Air Box?? Screen28


__________________________________________________
1995 K75 73,000 miles
The Air Box?? Usa-lo10
    

27Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Tue Nov 13, 2018 10:48 pm

Point-Seven-five

Point-Seven-five
Life time member
Life time member
Stacks will require a different ECU and programming to work with the throttle position sensor that replaces the MAF for determining air input for mixture calculations.  Mapping the correct mixture requires a fair bit of time on a dyno at around $100+ per hour.

Since most cafe projects seem to be just for photos and don't really need to run, I guess you could use the stacks and trailer the bike back and forth to photo locations.


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

28Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Wed Nov 14, 2018 7:31 am

Dai

Dai
Life time member
Life time member
@jahearne wrote:BSK has some cool looking throttle bodies with stacks
No use. They're for the 4-valve engine only where the Moronic unit does all the fuel/air calculations.


__________________________________________________
'83 K100 upgraded to K100RS spec
Others...
'78 Moto Guzzi 850-T3, '79 Moto Guzzi 850-T3 California,'93 Moto Guzzi 1100ie California,
'03 Suzuki Blandit GSF600SK3 (NFS any more because wifey has claimed it)
    

29Back to top Go down   The Air Box?? Empty Re: The Air Box?? on Wed Nov 14, 2018 8:19 am

charlie99

charlie99
VIP
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@Dai wrote:
@jahearne wrote:BSK has some cool looking throttle bodies with stacks
No use. They're for the 4-valve engine only where the Moronic unit does all the fuel/air calculations.

ben runs an after market  ecu

so suitable for his builds …
just a heads up

but yes  in normal practice  motronic ecu would be required


__________________________________________________
cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%OThe Air Box?? Au-log10

"redframe" rs "bitsa"  with many contributions from the k100 community ,,with many thanks
    

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