Airbox delete on a 4v k100, understanding

[Reinier]

Are you Dutch ?

I got this set https://www.caferacerwebshop.com/nl/powerbrick-luchtfilterset-bmw-k-serie.html

The tubes are 3d printed and fit perfectly. The filters are included and high quality.
I was concerned about getting filters with sufficient airflow. And the powerbrick website and the filter brand convinced me. But they are even more expensive.
And the fit in the black and red theme of the bike.

[Mill]

There appears to be little economy options out there.

And no, but my work sent me abroad to Nijmegen for a while.

[sooprvylyn]

I understand!

The 4-way is the connector for entry, not exit.

The reason I thought they were there were some sort of BMW engineering to sync airflow evenly though the carbs to alleviate pressure differences or something, but that is not the case at all rather its just oily/dirty air going to carbs to be re-burned. I will be blocking these off.


On a side note, did you get your 40mm intake manifolds from kpartsholland? or a different site? $226/€209 is quite expensive for the rubber and intakes

Dankje

It is correct, on a 4v k bike there is a lot of enviromental control in the air intake system.  You can remove the "4-way breather" and just put plastic caps on the small holes on the back of your throttle bodies.     Attach a catch can to the breather vent at teh back of the engine.  Attach pod filters or a plenum to the throttle bodies, and make a place for the o2 temp sensor to measure the intake air temp.   I have a bracket file if you need it for the air temp sensor.  Look in the 3d parts  forum.

For the intake boots, you can actually get some 40mm silicone boots on ebay that fit perfectly.  They come in red, blue and black. Here is the link: https://www.amazon.com/dp/B07QQQ83QL?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_9&th=1

The boot that is nearest to your throttle advance lever(choke) will seem like it wont fit, just tighten the clamp and you will see it does fit.


You can see the red silicone boots from teh link above, and also you can see the o2 temp sensor bracket I mentioned, in this photo.  This photo was taken before i removed the 4-way breather on back.   Now it is gone and only has small red plastic caps on teh holes.

LAst, there is a small hole above your timing chain cover just below the radiator.  Plug it with a silicone plug(heat resistant).  This hole is also part of the emissions system.  It allows the crank case breather oil to go back ito the engine.  Once you delete the airbox, it serves no function.  If you dont block it, the timing chain will spit some oil up from that hole and it will get on your engine

[sooprvylyn]

with the caps on the back

[sooprvylyn]

here is a video I made of my setup on my 4v bike.   Sorry for some of the stuttering, old phone.

[sooprvylyn]

Be aware that an airbox delete will remove a bunch of legally required emissions controls. If your bike must pass an emissions inspection, it will fail.

[Mill]

Yeah, Iowa doesn't have emissions at all. and a question I have is why didn't you put the temp sensor in the rubber to more directly know the temp going into the engine, I feel like there would be a difference in temp from inside and outside?

And where is your it vent for your catch can?

And If any OEM farings are re-installed, would you see any decrease in airflow to the pods, I plan on having fairing(s) still be somewhat installable for winter months of driving

Thank you a ton for the extra photos and video, helped ALOT!

[sooprvylyn]

The Air Temp Sensor ideally should go inside the intake if possible.  Many people will put it into the elbow/boot of one of the pods if there is room to do so, or into any plenum they use.  I dont think there is a marked difference between the air entering the pod and the air that is 1 inch away from the air entering the pod.  I havent noticed any issues with ignition with the setup I have, but yeah, if you can get it inside the actual intake its better.

Yes, if you put the big fairings back on the bike, you will restrict airflow, and you will also be sucking hot air from the radiator instead of cooler outside air.  The OEM setup sucks air from in front of the bike for this reason.  If you are planning to use fairings, I would recommend using a plenum and routing the filter/intake nozzle outside of where the fairings will sit.

The vent for my catch can is a small pod filter on the catch can.  Watch te video again and look carefully at the catch can, you should be able to see a small blue pod up there with silver caps(upper right side of the video frame).  If you want details about this specific catch can let me know. I can link you the parts I used and how I connected it all.  99% of catch cans you'll find on amazon or ebay are massive and have a flawed design.  The one I used took some trial and error to locate, but it comes with a mounting bracket and there are 2 pretty good places you could mount it on the bike, depending on what you are doing with your frame.  This catch can unscrews the cup from the cap for emptying, and the bracket is on the cap(ie you need no tools to empty it).

[jbt]

There are lot's of pictures of K's with pod filters but hardly any mention of what to do with the tubes connected to the airbox. 

What do you want to do? Take a photo of your K or ride it?
If you want to ride it, don't touch to the airbox.
An atmospheric engine, overall a fuel injected 4 inline motorcycle engine is designed to work with an airbox. The FI system needs to work properly that the intake is enclosed in a quiet environment, without turbulence. That's the first purpose of the airbox. It permits to  control the pressure and the amount of air available. Don't worry, the dimension of the airbox and the air filter is far enough: it could feed 4 K engines at full throttle. By the way, you'd be surprised how performance, measured on a power bench,  could be changed by a single subtle change of the intake airbox diameter...never to be enhanced, always to be degraded. BMW engineers of the eighties were not idiots. ( Today... )
Another purpose of the airbox is to measure the air temperature accurately: this is crucial for the ECU as, without air flow meter like there is on K2V, the amount of air sucked is estimated by its temperature in the airbox and the RpM value. You know that pressure and temperature are linked... By removing and relocating the air temperature sensor elsewhere without calibrating it or re-mapping the ECU, the value it sends will be inaccurate.
Crankase case pressure management is also important: if you reduce the ventilation flow of the crankcase, it will reduce power of the engine, but also will create stress on the gaskets and provoke oil leaks. If you replace it by an shiny chinese cheap air pod that will clog within a few kilometers, you will also have to face very regular maintenance issues.
Recycling oil vapors is another function of the airbox. Yes, I know, you don't care about environment policies. You probably have another source to breathe air, or gills?  But your engine needs this oil also. It lubricates, modestly but usefully, the admission valve stems and the guides. Why do you thing there are valve gaskets?
Last but not least, you will notice that when opening the airbox, each port has a velocity stack dedicated. With a very specific lenght and shape so it's accorded to erase flat spots of the power curve at some rpm . Remove it and replace it by standard crap pods and it will ruin the admission harmonics. And, at it is usually measure, will reduce the amount of air that could be admitted in the engine: anyway they will never improve it as it only depends of how the engine sucks.

If it's only to shine on social media, do anything anyhow.

[Kaos]

If you want to ride it, don't touch to the airbox

If you replace it by an shiny chinese cheap air pod that will clog within a few kilometers, you will also have to face very regular maintenance issues.

Not entirely true. I've done multiple tours (about 12k in kilometers since deletion) with a deleted airbox and MAF sensor on a 2 valve (using a temp sensor and a v2.1 ecu). And it runs and rides like sunshine. However, I am still in the phase of regular checks minor ajustments since I've came up with the solution of the airbox/maf sensor delete on a 2v.
Just do keep in mind some things might be different. It takes some fiddling with the intakes to get it smoothly [as in ajusting the throttle body].
You will probably have a higher fuel consumption. Well at least I do have more fuel consumption, but that was what I expected and was warned for.
What you'll notice on a cold bike with Low RPM that it tends to feel more clunky.

when it comes to an airfilter on the crankcasebreather, which I currently use (for a BMW M3) works fine, but its messy as hell. Dont recommend using an Airfilter.
I dont know about the clogging, since mine hasnt, but it sure as hell makes me have to clean the empty open oven. Also people dont like riding behind me. So 10/10 I would recommend a catchcan.

The Air Temp Sensor ideally should go inside the intake if possible.  Many people will put it into the elbow/boot of one of the pods if there is room to do so, or into any plenum they use.  I dont think there is a marked difference between the air entering the pod and the air that is 1 inch away from the air entering the pod.

Frankly there is having it out in the open will cause a detection of colder air due to airflow on a higher speed, than the actual air inside the elbow or airfilter. Would recommend sticking it inside the pod or elbow as close to the front as you can.

There appears to be little economy options out there.

Economy option: https://cafe4racer.eu/en/air-filter-adpaters-bmw-k-100-k75-k1100/23096-bmw-k1-k100-16v-k1100-set-of-4-air-filter-with-rubber-adapters.html?srsltid=AfmBOoqYe_aITbvwjbnArD1crIpD-XeYEJp_stHV5VQc-CPXq0V7p-7K
these fit perfectly and arent rebranded fancy smancy airfilters and you could always get some others later on. These are rubber elbows btw, not printed.
Otherwise check this dude's shop: https://customcaferacerparts.com/nl/collections/all  he spend quite a bit of effort to craft and design his sets.

When it comes to hoses. All  fuel hoses go back where they belong.
Airbox delete == airbox delete, this includes the hose to the crankcase and (can you call them that?) hoses from the plenum chamber to the throttle body.
If you are going to use a car CrankCase breather filter like me, it will come with a - i do believe 21mm hose + clamp, but dont pin me down on the size - and some catch cans do as well.
Other than that it's pretty straight forward

[Kaos]

here is a video I made of my setup on my 4v bike.   Sorry for some of the stuttering, old phone.

Fair is fair, looks good. But it also looks like you've overcomplicated it for yourself. Not as complicated like the dude i've met running Carburators on a k100. But still

[Reinier]

@jbt you are right with some points. This bike will not be a daily driver but a fun project for sunny days so looks are a part of it.
And as this a old police bike it is highly over engineerd. Maximum top speed is not a goal, or even allowed on the road. And as I have remover 50kg from a 300kg bike acceleration is great. So a little dip in performance ( if it would happen) is not a real problem.
I also think it depends on the quality of the filters.

And the BMW engineers where no Fools but they did have to work with the available materials and knowledge. An they where only human.
It breather is as critical as you say they should have made the cyclinic seperator maintanable and not fill it with materials that decrade over time and then seal it. After 30 years it does not work anymore and part of the filter can get in your engine. Also everybody has at sometime a leaking breather hose and that does not instantly result in the issues you described.

And a little extra maintenance ? After 250.000km it requires and deserves some extra maintenance anyway.

[Kaos]

or even allowed on the road.

And esp  the respective BMW hobbyist would never ever disobey any traffic laws   

In all fairness, stripped down without windshields none of us will hit the maximum speed without internal bleeding from the turbulence and lose all sense of comfort at 130 kmph plus

[sooprvylyn]

Fair is fair, looks good. But it also looks like you've overcomplicated it for yourself. Not as complicated like the dude i've met running Carburators on a k100. But still

What's complicated about my intake? It's about as uncomplicated as it can be.

[Kaos]

What's complicated about my intake? It's about as uncomplicated as it can be.

I am Used to the 2v throttlebody setup, and my 4v TB on a 2v,  and because of that I thought you've risen your throttlebody taking extra steps with all placements of the components, thus over complicating.
But I was wrong, I didnt think of the fact that I was looking at an actual 4v and not some hybrid frankensteined version.

[Laitch]

Fair is fair, looks good. But it also looks like you've overcomplicated it for yourself. Not as complicated like the dude i've met running Carburators on a k100. But still

But still, that Brick with the tri-carb setup looks pretty good—carburetors not withstanding. Here are some photos from 2024

[Kaos]

I do fancy the looks of it. All i've understood from the brick enthousiast i've encountered with his carbed k100 is that its quite a configuration hassle to get it running smoothly

[Laitch]

I do fancy the looks of it. All i've understood from the brick enthousiast i've encountered with his carbed k100 is that its quite a configuration hassle to get it running smoothly

If the carbs have clean passages and undamaged jets, all it should take is clean, high octane fuel, the experienced use of an accurate manometer, acute hearing, and good spark plugs. The use of E10 shouldn't be a problem. It certainly takes more effort than having an effective electronic engine management system, but think of the multitude of copulation opportunities it's sure to attract. The Brick's fuel injection system just isn't as shiny. 

[Kaos]

Sold.
If, and only if there appears another wild brick on my path this shall be the route ill take. From a wiring point of view this would be a pretty clean build.

[Laitch]

Sold.
If, and only if there appears another wild brick on my path this shall be the route ill take.

Maybe you'll find one of these 35 year-old Luftmeister systems discarded along your route.

[sooprvylyn]

Sold.

Was it the multitude of copulation opportunities that sealed the deal?

[Kaos]

Was it the multitude of copulation opportunities that sealed the deal?

I would be lying if I said it wasnt.

Maybe you'll find one of these 35 year-old Luftmeister systems discarded along your route.

These are somewhat of a holy grail. I would most definitely pick these up if they came on my path (unless they'd cost me a second mortgage)

also: 
airbox discussions are dangerous.

[Reinier]

Hi all,  it took some time. I had some other projects like a child's wedding. But the bike is finished ( some minor details still to do ).

The airbox is removed, the frame powder coated and the rest painted.

Here is a video of it's first startup after the build.

[Laitch]

I had some other projects like a child's wedding.

Isn't the minimum age for marriage Holland still 18 years? I've got to admit, it probably makes wedding gift-giving less expensive if it isn't—xboxes, skateboards, stuffed animals, dolls, gift certificates for Happy Meals at McDonald's, robotic puppies, Legos, etc.

[Kaos]

Isn't the minimum age for marriage Holland still 18 years?

Same as the USA. 16 to 18 with the parents consent, 18 is legal. However then you're allowed to drink at your own wedding. Still a child though and the groom would probably still be happy with an xbox. Bride.. less often.

Anyway. Good going Reinier. Hidden battery - a anti gravity batt under the tank? -
Did you do something with the can? As in sprayed it with some 2k?
Some unwanted advice. Go for a rear fender/mudguard otherwise you're going to have a bad time keeping it clean.