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Thread: 1986 BMW R65 airbox removal?

  1. #1

    1986 BMW R65 airbox removal?

    Has anyone successfully eliminated the airbox on the 1986 R65's
    Looking to clean up that section of the bike and thinking filter directly mounted to the carbs would look much better.

    Reason I ask is all the extra hoses etc that run thru there and what they operate.

    Any help is appreciated

  2. #2
    MOA #24991 Pauls1150's Avatar
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    The "extra" stuff is the "secondary air system"; sorry but I don't have the details on that and don't know if it can be pulled off as easily as the system on some of the larger R bikes.

    Be advised that separate filters (sometimes called "pods", like the conical clamp-ons) probably will NOT breathe as well as having a complete airbox ... which may be why nobody else has responded yet.

    From Snowbum's website:
    "For an all-out motor for racing; individually mechanically supported gauze intake horns to avoid fuel foaming from vibration are desirable, but these do NOT work well for street/touring, where the clamshell or square air-cleaners are far better, particularly if insulated from engine heat. Even the original paper filter elements are BETTER than those racy-looking intakes!
    ...
    Definitely give a lot of thought to additional air, COLDER air, to the intake system. A very significant power boost can be had. Insulating the intake system can be very helpful, if you are using, more or less, the standard rectangular airbox and snorkels. Help for the clam shell type is also had. This type has far too much heat given to the intake air. If you use the rectangular airbox system with its snorkels, vast tuning possibilities exist, for both street and mild to moderate racing. With some insulation, performance is quite enhanced, with proper jetting, etc. By modifying the snorkels, you can move the torque peak all over the place!"

  3. #3
    Airmarshal-IL James.A's Avatar
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    There are 2 systems at work in an un-modified air cleaner assembly with the square filter. The crank case ventilation system delivers the oily mist from the motor bottom end in to the carburetors to be burned up. You will have to deal with that. Additionally, your bike would have originally been delivered with a "Pulse Air" system as an emission control device. This system delivers filtered air from the air cleaner box to the exhaust port on the head(s) to facilitate the burning of any pollutants in the exhaust. Many have been removed and blocked off, but we still occasionally find a motorbike with that system intact. The motor will run just fine if the pulse air system was removed and all the plumbing plugged up and dealt with correctly. The crank case ventilation system is another matter. What some owners do for that is to extend a hose to deliver the misted motor oil to the atmosphere. I have seen these draped to the underside of the transmission or extended to the rear of the bike near the tail light. Zip ties are usually involved in securing the extension to where ever it is placed.
    1973 R75/5

  4. #4
    Registered User STEVENRANKIN's Avatar
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    Oil breather lines

    I have seen people route the oil breather lines both properly and improperly when they "removed" the air filter system to go to carburetor cone filters as a "performance" modification. In the case of improperly routed or conceived oil breather systems, Oil mist can build up places it is not supposed to, and occasionally there is enough oil blown out the system to cause puddles (worn engines are most likely for this to happen).

    I removed the pulse air system and plugged it on my bike years ago when it quit working, it is not difficult to do and does not cost a lot. There is NO noticeable performance difference I can find. I didn't remove the system for performance reasons, I just didn't see myself paying the cost of BMW parts to make it work again for what little it may have been doing.

    As for removing the air cleaner, and going to cones on the carbs, in all honestly, there are people who swear it makes a terrific HP increase. I find most of the people I know who did this reverted back to the stock air filter system because A; they couldn't see huge difference in performance. B; the cone filters don't filter nearly as well as the stock system. Finally C; the oil breather line and dealing with the oil mist from the crankcase was a pain to deal with using the methods the owners used.

    Don't get me wrong, I am NOT against increasing HP and torque but, I question a lot of people's methods and their results. the 2hp and 4ftlbs of torque you might get out of putting cones on along with the messing around resetting the carbs and rerouting the oil breather, in my mind just is not worth the effort on a street bike. Oh yeah on a race bike, every HP and ftlb may mean the difference between first and second place.

    I ride briskly and smoothly on the streets and my bikes in normal stock tune and configuration work very well for my style of riding. Personally, I have installed fork braces and suspension enhancement with noticeable difference in handling. But, any change I have done to the engines would not be worth the cost to me. Let me put it this way, back when I first started riding this bike, I was riding a whole lot faster and more aggressively than now. I got it in my head, I needed to buy "sport" tires so I could ride better. After a summer of wearing out four sport tires, I went back to touring tires and found the performance difference for my riding style meant I has wasted a ton of money on sport tires. I couldn't tell the difference.

    As I have said in other posts today, I am bored, it is raining, so I am bugging people on the forum. St.

  5. #5
    MOA #24991 Pauls1150's Avatar
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    Bug away, and send us some of your rain!

    With an airbox setup, the air is literally channeled directly to the carbs' or throttle bodies' intakes, but with pods, there is only turbulence surrounding them. It may work at higher speeds and rpm, but as you point out, why bother if it's just a "street" bike. Also, on MANY bikes (not just BMWs) and cars, that box is actually a significant part of the overall engine tuning.

  6. #6
    Liaison 20774's Avatar
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    Paul brings up a good point. LKChris has pointed out in the past that the middle initial of BMW stands for motor. I would hand it to the engine designers to figure out what works and what gives overall good performance. It's typically a zero-sum game...you might be able to improve the top end but you might suffer in the mid range.

    And this reminds me of something I read quite some time ago. We think of the air coming into the carbs as just a steady stream of air, when in reality it is in the form of pulses. The air is pulled into the intake tract due to the intake valve being open and the piston moving to BDC. But then the intake valve closes. What happens to that inrush of air? It tends to bounce against the closed system and create a wave back the other way...in essence a series of standing waves are created. Ideally, the wave needs to be coming towards the intake valve, but if for some reason, the intake tract timing creates a slight "vacuum" or negative pressure area right in front of the valve, that will hurt performance.

    I think one potential example of intact tract tuning is what BMW did for the lowly R25/3. The R25/2 has a whopping 12hp...DAMHIK!!! The intake tract is pretty basic...there's a "rock strainer" filter on the aft side leading to a tube through the carb towards the intake valve. For the R25/3, then actually moved the opening for the air in front of the gas tank, down low. The intake tract is built into the tank. That was routed around to behind the carb, then turned forward at the usual spot. The results...13hp!! Small value for horsepower increase, but it was around 8% increase...wowser! There might have been some ram effect, but for whatever reason, likely all together, they got the air intake to match up better with the valve operation. For the R26, they went to a different intake system.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  7. #7
    Registered User STEVENRANKIN's Avatar
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    I concur

    Yep, the BMW guys really do know their stuff, and it shows in the quality of the airheads, the performance available at the time for each bike as designed within parameters set by physics, and the EPA later.

    Quite a few years back, we had a radio host who was on the air early in the morning. He would leave his quiet suburban cut de sac at two riding his HOG with straight pipes. He was on the air one day bemoaning the fact his neighbors had turned him in for his loud pipes and he had been given a fix it award. Of course, a vast majority of people called in with support in regard to his right to have loud pipes and such nonsense but, and here I tuned out, later someone big into the HOG scene contacted him and gave him an education regarding HP, torque back pressure, and a whole lot of very good knowledge. The DJ installed a pair of mufflers and was surprised how much better his bike performed as well as being happy the neighbors weren't going to shoot him anymore. He learned the fact that what works on a race track to add performance, Ie open pipes makes no sense on the street and may impair real road performance.

    I am not a race engine builder, don't race, and don't like spending money unless I see major results, I don't like making needless work for myself unless there is a big reward. So, I go with the BMW design, and despite what some people say, I avoid things like air cone filters fitted to the carbs, and open pipes. While they may be great on a race track, I ain't riding on a race track.

    let me see, an 8% gain on my R80RT would be 4HP, not bad if the gain was cheap and easy, but not much for a big buck of parts and labor. LOL by labor I mean taking the hour of wrenching or so to reset the carbs after adding cone filters. Lazy am I. St.

  8. #8
    Thank you everyone for the replies!!!
    Seem like a great bunch here and HELPFUL!

    Will post some pics of the build

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