I have a 1981 R80 G/S with a 1980 R100 motor in it. This engine has the later model starter cover and flat, plastic air cleaner box, though. Want to convert it back to the old style. I have the parts, but will bolt right up? What do I do about the breather that currently dumps into the air cleaner, and will removing the snorkel setup and changing the filter affect the running in any way? Thanks in advance, Joel Parks Yonkers, NY
Yes they will bolt up... but yes, you will want to do something with the oil breather. The old system simply dumped it into one side (right side?), but you can probably come up with something clever. You do know that the "old style" starter cover was different as well? It takes the starter cover with the curve-upwards, and the round-air-filter air cover. I did it on an R100 just 'cuz I like the looks of the old style....
The old style airbox, filter and starter cover (must use old style for all three) doesn't breath as well as the new style. So this will leave you running a bit rich. i wouldn't worry about it. Build it, run it and then adjust jetting if needed. Jets are cheap. if you look at the diagram here you see the windage setup on top of the block. Seems to me part #2 is for the old style with a hose to the Right intake and Part #3 is for the new style. http://www.ascycles.com/Illustrated...ngine&bindName=Engine_housing&bindCat=11_1725 This shows an old style starter cover and windage assembly. You need it all. http://www.ascycles.com/Illustrated...e&bindName=ENGINE_VENTILATION&bindCat=11_1734 This shows old and new style starter covers. The one with the slots (rather than the scoops) is for the flat airbox) /crap, lost thye link, well, you'll find it/ The new style windage feeds both sides. http://www.ascycles.com/Illustrated...e&bindName=ENGINE_VENTILATION&bindCat=11_1755
If you are using the stock breather set up you will need 79 on air filter housing and these 2 breather hoses 11 15 1 335 733 and 11 15 1 335 734.
When Rob Farmer was chasing a mixture problem he fitted a "O2" meter to his RS? which he could read out on the road, and found that the flat filter didnt flow enough at high revs , and stuffed up the mixture. He fitted a old style round filter which flowed better, and didnt affect the mixture as much at high revs, but it still wasnt perfect. Last I can recall he was working on modifying a flat filter so it did flow enough. So he got the opposite result to Plaka. But I am not saying either is wrong. Same thing with the snorkel set up - some folks remove them from the flat air boxes and their bikes will hardly run - others get an all round improvement in throttle response and much sweeter running. So , what is true and undeniable for some folks just doesnt work for others. I suggest you just try what you want and see what happens. And if it doesnt work as planned on your bike, try and figure out why - every bike is the sum of its parts and your bike probably has some parts different from other bikes. Some folks extend the breather hose out to a catch can in behind the battery somewhere, and vent the can through a auto breather filter - from an engineering viewpoint you want as little oil in the combustion chamber as possible anyway.
As it is often found with airheads, the devil is in the detail, not all of the Old style airbox covers are the same as they were altered to accommodate revised crankcase breather systems, if you get it wrong you could end up with an airbox that feeds unfiltered air to your engine. Jim Cray's approach to improving the breathing to flat air boxes is to reduce the length of the snorkels by about 1/2 and cutting 4 x 1.5inch diameter holes in the top of the filter cover. This does require a waterproof air filter element such as a K&N.
I like the square boxes better so I just stuck with that. I think they look just fine. I think they are a lot easier to work with. Other that removing all the air pump crap, anything I have done to them on a stock engine just kills midrange for virtually no better top end. Sport mufflers, sport cam, Dellorto's, slightly cleaned up ports. Same story. Changing the setup in about any way killed midrange. Then I raised the compression a lot and really hogged the ports out. Tons more midrange but my top end seemed a little soft. The first thing I did was take the top and filter completely off. Close to the same midrange this time! That never happened before! Up above fell flat on it's face. Rejetted from 135 mains to 165's. Now I had a lot more on top with about the same midrange. The I cut the rubber velocity stacks to just bell mouths inside of the box for a lot more midrange yet. I put just the filter on the box. No diff. I put the filter and a top with the entire top cut out of it. No diff. That's what I am running now for a big gain on top AND in the middle. No top got me more top end and much shorter velocity stacks got me more midrange. I think those stacks are setup stock to help BELOW midrange and that's how shortening them got me more midrange. In other words, they are still too long to help top end. With my latest setup that is. It ALL depends on what you've got!
if you plug any unused holes on the engine side of the filter housing you don't have to worry about unfiltered air. The round filters could be crushed if you installed them carelessly and then they wouldn't seal around the rim. The K&N sometimes had this problem. They were a bit too small and wouldn't fit around the pins easily. I've seen QA problems on the flat K&Ns too. A recent article I read indicated that while they do flow better they filter worse. I won't be using one again. measuring the flow through a filter is very simple and pretty cheap. You use a mechanical differential manometer. Dwyer makes them (intended for permanent installation across filter banks, I've installed them in auto paint booths) but you can make your own with a length of plastic tubing, some water and maybe a bit of food coloring. You can set one up on your airbox in the driveway and then just wind the motor up and watch the pressure change. Also handy for knowing when your filter is getting clogged and needing changed. The trick with the flat airboxes is that they are a tuned system. I recall BMW made a number of changes to the snorkels trying to get the tuning right. The latest version (two long snorkels) is considered the best. If you bore holes in the top of the box you just screwed up the tuning. You might want to do this to get better flow at a particular RPM (and tune the carbs for that) but my guess is you would lose tractibility throughout the RPM range. The carbs are depending on a particular airflow/mass through the venturi to operate. The CV carb has a vacuum operated piston that adjusts both the effective throttle opening and the mixture at the same time. Pretty sensitive to flow. Good touring carb. Not so great performance carb. At any rate if you aren't getting as much air as you want at high RPM, just decrease the main jet size. But I would assume someone looking for high rpm performance is not using CV carbs. A carb change could push the upstream tuning out of it's envelope and all bets are off. As an aside, those flat filters are $$$. I'm thinking of making up a simple pressure testing box to evaluate them so I know when to change them---and when not to. Couple of boards, a manometer and a shopvac running without a filter to provide a known airflow.
"The trick with the flat airboxes is that they are a tuned system. I recall BMW made a number of changes to the snorkels trying to get the tuning right. The latest version (two long snorkels) is considered the best. If you bore holes in the top of the box you just screwed up the tuning. You might want to do this to get better flow at a particular RPM (and tune the carbs for that) but my guess is you would lose tractibility throughout the RPM range." I think it's fair to say that a stock airhead IS a tuned system, any changes will affect that system . Jim is a very well respected UK based tuner who does check his work on a dyno. His alterations to the airbox were done as well as porting, dual plugging and squish band modifications. At that time the engine had standard carbs and silencers and went very well indeed. I'm fully aware of various discussions regarding K&N filters.
When did those tops have anything but the same length horns? Cast or plastic? They first came in sand cast aluminum. Those are the tops that had the bulletins and whatnot for their castings being very irregular. The plastic caps have always had one large/one small and two large horn tops. All the horns are the same length. Stock to modified with cam, carbs, and exhaust I thought my setup ran best with a stock one small/one large horn setup. Modifying it past that changed everything. It know runs best with no top at all. I have read many an internet report that K+N's don't filter as well as the stock paper filters. Judging from the amount of dirt I have seen get into square airboxes with stock paper filters compared to K+N's, K+N's filter TEN times better than the stock paper filters. I have changed literally hundreds of filters in those boxes and, from what I can see with my own eyes, properly maintained and oiled K+N's filter better than any setup I have seen. That's the only reason why I use them. K+N's keep my box and snorkels SPOTLESS. Stock and foam has those boxes looking like a cat's well used litter box. I have seen this difference bear out time after time after time. The tests? I have looked into a couple and they were right there with photos testing K+N's with virtually no oil on them. They don't filter like that. I can tell you that. On that subject I think it is funny that 9 out of 10 K+N type filters I see here on the net and in person do not have enough oil on them to filter properly and it is not hard at all to keep them oiled properly!
I don't think BMW was even trying to tune the intake until they went to the flat filters. They fielded normally aspirated race bikes, they had the technology, but they didn't put it on the street. I gather they saw their niche as reliable, long lived touring bikes. They offered factory luggage instead. When they started slipping backwards and loosing HP to emission restrictions, then they started playing with the intake. I found I can do all sorts of stuff to the airhead motor to make it more powerful (I had a reasonably firebreathing 90/5 once) but then I gotta do even more stuff to the chassis and brakes or all I've got is a stoplight dragster that likes to rip the spline hub off the crown wheel (only time I had to push that bike home). i'm currently building my '83 R100 motor back to the '77 spec because I live at high altitude (no oxygen) and burn the boiled boar urine that they sell for gas around here (no BTUs)...major decrease in HP and mileage. But it's still an airhead. It does very well those things that airheads do very well. If I wanted a competent sport bike I'd go buy one. Back in the day I can see playing a lot with the tuning, but not now. That said, I do have a spare upper airbox and snorkels, I might screw with it and see what I can get
Plaka, I think that BMW was more concerned in the the early 80s about getting their bike through increasily difficult Noise and emission regs. I think that improved airhead engines are great, helps you keep up with modern traffic that goes much faster than it did 35 years ago. I agree that some attention to brakes and suspension is needed!
Ya, especially California. To my knowledge there were no Ca. specific models so they were applying those standards to everything. of course the first thing the owners did was rip off the emissions crap (and they still do). Some of it was harmless ( aside from extra complexity and weight) but other stuff hurt the HP. I was just going through jim Roches article on road rod tuning. With high flow heads and exhaust he is drilling big holes in the top and back of the dual snorkel airboxes. I've seen drilled drum style airboxes as well but I suspect it's cafe racer styling more than anything. I'm running a very high flow exhaust but I haven't fooled with the intake tract until I get the fresh heads in. I'm working on some thermal efficiency issues and I want to finish that up first as it may involve adding some ductwork to the airbox. If I end up doing this I'll add a mild ram air directly into the airbox to try to recover sea level pressures in the box at speed (60-90mph). I had a K100RS for a while and while there were some things to like about it and a whole lot not to like, one of the bottoms lines was that it was too fast (even with a changed rear ratio). I sold it.
Plaka -air flow aint the only thing that affects the slide position - ever wondered why SU sell eight different slide springs? They fit Bings------. BMW list two, and it is always worth trying the late, stiffer version.
I spent some time on the Dyno with my PD seeing what worked and didn't work The flat airbox was spot on for bikes fitted with 32mm carbs but just didn't flow enough air for my 40mm carbed bike. The problem I had was the lack of main jet sizes for the bings. The early airbox made the mixture too weak at the top end and I couldn't buy main jets in the right size to get it right.I really want to fit a set of Amal mark II carbs before I start messing around again. What you do appear to get with the early airbox, as long as you have the higher comp pistons, is a much more linear power delivery. My PD going though it's paces. You can see the early airbox. I also had it rigged with a air/fuel ratio meter for road testing This is an interesting read
Since your post about your findings is often brought up in airbox discussions Rob, I think is important to point out that it is actually the airbox top and not the airbox itself or the filter that is actually restrictive. Well, that and those stock velocity stacks. For instance, in '95 San Jose's race bike Wrecking Ball broke ALL BMW Daytona track records and it was using a square airbox. Without the top, of course. After modifying my bike to a higher level, I run my square airbox with no top but the filter itself doesn't effect the mix any appreciateable amount. I suspect it might work better than a claim shell in that you can have two big bell mouth stacks underneath a filter in a square airbox. My box is now basically a velocity stack support with a filter on top at this point.
They can't get it right? I thought you were supposed to poke a few pinholes in the diaphragms to tune slide motion?? You can file down the needles too to reduce the weight on the piston. Seriously, if you went with a stiffer spring would you be going after an altered torque curve?
Don't forget the lift holes in the slide. That's why modern jet kits come with not only different springs but quite often a drill bit to change the lift hole diameter.
