Hey everyone,

I want to start getting ideas for my 1987 K100 Resto / Cafe build. I am not particularly sure what route I want to go or what I want it to look like, but one thing that has been on my mind for a while is the intake setup. Being a 1987, I am under the impression that I don't have many options. What is the best-looking / appealing intake setup that you've seen or run? 

Thanks!

Keedo wrote: What is the best-looking / appealing intake setup that you've seen or run? 

Thanks!

The OEM one. Others can't run.

What's not being said is that the AFM unit is required to send a signal about the airflow and thus can't be removed.

You will see cone filters attached directly to the AFM, with the airbox removed. Personally I think that looks pretty janky.

My favorite solution is mine of course. Instead of the snorkel I use a small velocity stack esque inlet with it's own mesh screen to keep large debris out.

I don't see much reason to remove the airbox entirely. Unless you are really going to dedicate effort into rewiring and removing the fusebox as well, you will always have plastic boxes under the tank.

https://imgur.com/LjfsGlO

It's pointless to use a velocity stack here. There's a lot of obstacles before the air reaches the intake valve: air filter, flowmeter...any gain of air speed will anyway be instantly lost once the velocity stack ends into the airbox. Dura Bernouilli lex, sed lex.
And there are genuine velocity stacks into the airbox, but directly fitted to the throttle bodies! Well hidden, but there are:





And they even are finely tuned to give the best intake resonance and the best flow possible to the head port.
Removing the airbox will only have negative consequences. The flowmeter is calibrated to work into a quiet environment, with a constant air pressure that the airbox provides.
If you watch the genuine schnorkel, the diameter of it section is increasing from the intake to the airbox: this is to reduce air pressure and turbulences by reducing its speed. It's the very opposite of a velocity stack.
Note that the OEM air filter is absolutely not a restriction to the airflow. There's no difference of power output on a dyno whether there is a filter or not.
And, as always, it's not because you create a big hole for the air to come into an engine that the engine will pump more air. That's because an engine can pump more air (bigger bore, longer intake valve opening) that you have to enlarge the air admission. No confusion between cause and effect!

I think we can agree there is no functional difference, owing to the large airbox, the restriction of the AFM, the apt plenum and internal velocity stacks. Dura lex, sed lex.

The 90 degree turn at the base of the snorkel into the airbox also owing to it's own inefficiencies and lack of import. Rather it serves it's purpose as an inlet for air colder than what you'd find bottled up in the fairings.


All of this ignoring that the OP asked a question based on appearances.

Correct, this is solely for aesthetics. I am not building the bike for performance.

The question is not how to increase or not performance, but how not to reduce it for aesthetics...

Keedo wrote:Correct, this is solely for aesthetics. I am not building the bike for performance.

https://pipeburn.com/beastly-brick-bmw-k100-silverback-gorilla-by-two-wheels-empire/

I kind of dig the plenum side of this one. I like seeing the more pronounced individual routing on the intakes.

The airbox side is done better than others I see, but the photos are dark so hard to say what they've done with the AFM. Buried in there somewhere. About as much modification as you could do on the intake bits.


Clever bit of dress-up on the plenum on this one. But the AFM with a small cone filter fitted and just sort of awkwardly hanging out isn't much of a solution to me. I think it warrants more attention and actual fab if you go that route. Just my opinion of course.
https://pipeburn.com/bmw-k100-ed-turner-motorcycles/

On the first bike the AFM is mounted off the frame rails. Also that 'ram air' setup is more likely to destroy the air flow than make it better, unless the intake length has been tuned (it hasn't. For example, a reverse-head Triumph T140V needs six inches of intake to slow the air down enough for the carbs to use it. Kawasaki tried ram air in the mid-Nineties as a sales gimmick and ended up with over two feet of intake though fairing ducts before the air flow was useable).

On the second bike the AFM is hanging in the breeze as on most K100 customs. The only pic that shows the AFM directly is slightly confusing because there's a cable running in front of it. However, this one is only the second custom I've seen that has successfully dealt with the tank/subframe line.

jbt wrote:The question is not how to increase or not performance, but how not to reduce it for aesthetics...

A very good point often not realised along with what Dai says.

If it's all about aesthetics, well, don't ask any questions. Do it.
You'll be altering another K to make one more boring clone, so-called racer, with all the fashionista's gimmicks and the full set of uniform gear on it: the saddle (brown, mandatory brown, to respect the original look of vintage seats that all were actually black) too short to be usable ("It's OK, I'll never ride with a passenger anyway"), the too short too large fork with a reduced offset that will smash the tank ("It's OK, I'll never turn at full angle anyway"), an altered angle that will give a terrible agressive look but a very poor road handling ("It's OK, I'm riding carefully anyway"), the missing fenders ("It's OK, I'll never ride in rain anyway") that hardly hide too large off road tyres ("it's OK, I won't really ride off road anyway"), the rear one being fitted on a too large and misaligned rim (It's OK, I'll never post on Instagram any rear view anyway).
And to make sure that everybody notices this so casual unique clone, of course, a shorten but noisy exhaust that will complete the list of alterations of the essential qualities of this bike ("It's OK, I'll ride only out of town, anyway")
Fortunately, the crappy chinese instruments and "simplified" wiring will protect you to be affected by all these alterations. ("It's OK, I won't ever get it running nor ride it anyway").

jbt wrote:If it's all about aesthetics, well, don't ask any questions. Do it.
You'll be altering another K to make one more boring clone, so-called racer, with all the fashionista's gimmicks and the full set of uniform gear on it: the saddle (brown, mandatory brown, to respect the original look of vintage seats that all were actually black) too short to be usable  ("It's OK, I'll never ride with a passenger anyway"), the too short too large fork with a reduced offset that will smash the tank ("It's OK, I'll never turn at full angle anyway"), an altered angle that will give a terrible agressive look but a very poor road handling ("It's OK, I'm riding carefully anyway"), the missing fenders ("It's OK, I'll never ride in rain anyway") that hardly hide too large off road tyres ("it's OK, I won't really ride off road anyway"), the rear one being fitted on a too large and misaligned rim (It's OK, I'll never post on Instagram any rear view anyway).
And to make sure that everybody notices this so casual unique clone, of course, a shorten but noisy exhaust that will complete the list of alterations of the essential qualities of this bike ("It's OK, I'll ride only out of town, anyway")
Fortunately, the crappy chinese instruments and "simplified" wiring will protect you to be affected by all these alterations. ("It's OK, I won't ever get it running nor ride it anyway").

Priceless!!!

I would add "it's OK, I'm just building it to take cool urban wasteland photos of the bike so I can post them on the interweb, and turn on some cool girl with green hair, black eyes and clothes, and a face full of fishing tackle".

"Now get offa my lawn!"
 

Two Wheels Better wrote:"Now get offa my lawn!"
 

However, feel free to drop off the Brick's fairings fenders, seat, rear cowl, instrument cluster and related hardware. The gardener will collect them and put them in the shed.

This gardener has been collecting and storing their cast-offs in his shed (and garage, and attic)...in the hope the trend will end and some will wish to get dressed.

Tough crowd 

Not really, honestly.

Keedo wrote:Tough crowd 

A complete vitriol for anything K100 cafe is a signature K100 forum characteristic.


Feel free to PM me if you have questions. I've been through it all to complete mine. I ride it more than I do my RT.

I think the world weariness (rather than vitriol) comes from seeing so many bikes being butchered to be turned into cafe racers and never finished because the builders don't think ahead or think it through before starting. Those that do get finished (usually from a 'professional' shop) almost always ignore the visual problem with using a K100 as a donor and that is the tank/seat line, so the finished product never looks right. There are ways around that problem but in X years of being on this forum I have only seen three bikes that solved it and one of them was built by a forum member from scratch (yes Chris - I'm looking at you). 

The second major problem is that instead of thinking ahead with the fuel tank, there seems to be this sort-of panic that because the fuel pump is inside the tank then you can't use any other fuel tank. Not so - Moto Guzzi use an external fuel pump.

Lastly, the eight-valve engine is the wrong engine to use for such a project because of the AFM. It would be far, far better to start with a sixteen-valve engine because it doesn't have an AFM. Look at this one:

https://www.youtube.com/watch?v=fU6eHCfb9ww

That is a good cafe racer - seat/tank line solved, sixteen-valve engine and a change of fuel tank. We are not anti-cafe racer/anti-custom/K100 purists (both of mine have been hacked about in one way or another); check this thread out too:

https://www.k100-forum.com/t13161-k75-madass

Finally, if we really were anti-cafe racer then there wouldn't be a sparate forum especially for those builds. There's a lot of help in there too.

And further to what Dai says like any forum there are the crusty old pensioners with too much time on their hands who cannot help themselves and just have to criticise those of a younger generation.  Grumpy old men* who always did it better in their day and over the intervening years have lost any sense of humour that they ever had.  

We are fortunate on this forum as it is well moderated and any attempts at character assassination are shut down.  There are other forums out there which are aggressive and unwelcoming and this one definitely is not.












*  I'm working on it.

Dai wrote:  

Finally, if we really were anti-cafe racer then there wouldn't be a sparate forum especially for those builds. There's a lot of help in there too.

I'm not an anti-cafe racer. At all. I've been building BMW cafe racers some since 1995, when Internet, Instagram or Aliexpress did not exist. In those days, making a racer was really meaning to make it.
I built this one from a R75/5 20 years ago, and rode it a lot on road, hill climbing and for mountain roads japanese pilots taming.


I just don't like copycats using a inadequate basis to aproximately tinker a bike by shopping trendy parts without considering ergonomics, harmony or efficiency in their "work".
Make sparks, stack parts, park crap.

But I sincerely admire those who create their own racer, making it from scratch and paying attention to the consistency of the design and concept.

I like seeing someone do a nice job on a cafe. I hate seeing someone hack a good 75. But for me motorcycles are to have fun with so if it puts a smile on your face, that's cool.

Note: Chris, It will not bother me if you do as many 75s as you can.

The ultimate solution for those who wish to appear to have a clean intake system whilst retaining the full function of the airbox. Available in handy three or four packs for the café-d out engine of your choice.
 
Sort of clips on like a bow tie for your convenience. I reckon it'd make a swell addition to any K bike out for the day on the Distinguished Gentleman's Ride.

Don't forget to drill holes in the airbox of the same diameter of these velocity stacks to align them or they will have no effect at all...

A closer look. 

About these velocity stacks, I changed the ones installed on my R75/5 racer, made from...old cup trophies, for new shiny aluminium aftermarket ones. Because I got them for 10€ only.
Test ride yesterday: the engine has lost a lot of power at high RPM... The only difference is that the new ones are 1 cm shorter. That's enough to ruin the resonance previously set up to enhance the performance at high RPM.