Airhead airbox

Discussion in 'Airheads' started by vacantstare, Sep 28, 2010.

  1. vacantstare

    vacantstare Been here awhile

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    I am very close to purchasing my first airhead, and one of the candidates is an early 80s r100. I like a lot about it, but one thing I hate is the plastic looking airbox. I know the air filter design changed at some point (79ish?). Could one, if they were not concerned about preserving the stock configuration, replace that airbox with one of the earlier design?
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  2. Sniper X

    Sniper X De Oppresso Liber

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    Good question as a buddy of mine with a 86 R80 wants to do the same thing for asthetic reasons as well.
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  3. Beater

    Beater The Bavarian Butcher

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    Ya'll correct me if I'm wrong, but it can be done ... but you need more parts than you think. You need the two airbox covers, the two carburator air tubes, new filter, the long bolt, and several shims/holders so the tranny and engine block can 'hold' the case.

    But in a word ... it can be done, and I do like the aluminum one's over the plastic ones ... but a word of caution ... the aluminum one's use a hard to find air filter and they are a PITA.
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  4. Sniper X

    Sniper X De Oppresso Liber

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    I was going to look at my air filter this weekend on my 1978 R100RS, by PITA what do you mean? Hard to get back in right?
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  5. wirewrkr

    wirewrkr the thread-killer

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    There's nothing hard to find about the70-79 round airfilter and associated parts. You must have gotten some bad info somewhere.
    Actually some performance oriented folks claim that there is better airflow with the early round style because of more surface area than with the flat airfilter.
    Also the round airfilter is way cheaper than the flat one, and easy to find. BMW dealers have plenty of access to them.
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  6. wirewrkr

    wirewrkr the thread-killer

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    Very doable BUT, you should find the latest air filter housing (79)
    that has the two breather hoses rather than the single one. Use all the associated plumbing from the 79 model and you'll be fine.
    If you try and go backwards with the engine breathing, your motor won't be very happy.
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  7. bmwrench

    bmwrench Long timer

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    Get a '79-only starter cover while you're at it. It will match the line of the early airbox and won't have the rubber hood to deal with-it has a cast in hood/scoop.
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  8. vacantstare

    vacantstare Been here awhile

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    Ah, I hadn't thought about the fact that the crankcase breather is in there. You guys give great info- thanks again.
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  9. Rob Farmer

    Rob Farmer Long timer

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    I've got one on mine. They flow more air than the standard box if you have 40mm carbs fitted. I fitted mine to sort out a jetting issue with my non standard engine. There are two clamshell covers to choose from. The larger carb machines have a perforated one to flow more air. The cover for bikes with 32mm carbs is completely enclosed and relies on the starter motor cover to supply air into it.

    As mentioned by the guys above you need the starter motor cover to go with it and will have to mix and match breather pipes. The standard inlet tubes on mine simply swapped straight over.

    You will need the wire clip and small cover from the early bikes that stop all the crap from the clutch being blown up into the air filters. Parts 10 & 11 on the diagram.

    There are a few bits and pieces to sorting it all out but they are cheap straight from the dealer.

    [​IMG]

    You do get more induction noise but thats not a bad thing.

    [​IMG]
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  10. supershaft

    supershaft because I can

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    They flow more air? That is debatable since some think the later boxes flow more. For instance, the last road race versions of San Jose's Wrecking Ball had a square airbox. It was running better than ever like that before he put a pressurized box on it for land speed records. My own non standard sport cammed, 38mm Dell'ed, ported, and piped R100 jetted perfect with the square box. I even run one large and one small intake horn versus two large ones because the two large horns give up too much midrange for very little gain if any anywhere else. Of course, the air pumps are gone and I run my crankcase breather out the back door. I think the square boxes are easier to work on too. Looks? I don't think I have ever given that much thought. I guess they look alright to me.
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  11. AntonLargiader

    AntonLargiader Long timer

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    Quoting the whole post with pic clutters the thread up a bit...
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  12. Rob Farmer

    Rob Farmer Long timer

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    Sorted mine out a treat and all setup on dyno. Make your own descisions.
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  13. supershaft

    supershaft because I can

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    Make your own decisions? + a Mcmillion. That is exactly why I am adding a different view on the subject.

    Wrecking Ball had just a bit of setup time on the dyno!

    Anton, I will try to figure out how to axe the photos next time.
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  14. Max Headroom

    Max Headroom lost in the '70s

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    By now you'll have figured out that it's a fairly straightforward exercise to retrofit an earlier airbox as long as you have access to the bits you'll need, and that for most purposes (perhaps other than racing) you won't notice any significant difference.
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  15. supershaft

    supershaft because I can

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    I don't know about that. The air horns and velocity stacks in those square airboxes are tuned real well for midrange. There very well could be a significant difference. You are right in that since he is just getting the bike, if there is a difference he won't notice it.
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  16. Max Headroom

    Max Headroom lost in the '70s

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    I would consider the definition of "a significant difference" to imply something in the order of 20% or more. An airbox change on its own won't do that, 'cos if it did, those of us with earlier bikes would all be changing over to the later pancake filters in the quest for free horsepower. The later bikes deliver their peak power and torque at lower rpm compared to the earlier bikes, but that was in tandem with changes to compression ratio, electronic ignition, jetting and cam timing. The biggest factor with the improved midrange on the later airheads was attributed at the time to the second exhaust balance pipe IIRC.
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  17. Rob Farmer

    Rob Farmer Long timer

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    Since it's got nothing to do with the original question Let's save this argument For another place.
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  18. supershaft

    supershaft because I can

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    Who's arguing? We've got your experience and mine. Two different takes on the same subject. Nothing to do with the original question? What are we talking about? Airboxes?
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  19. supershaft

    supershaft because I can

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    Is that what you consider a significant difference? 20%? Or more? I thought significant meant anything of meaning or consequence? That comes in fifths for you? Slow down and take one sip at time. :norton

    Even by your high standards, an airbox change alone can do that. For instance, with my bike changing just one air horn from a small one to a large one would net you a significant drop in power at a particular rpm right around 3500. No, that isn't across the board but . . . . It isn't on a race track either.

    But that couldn't be 'cos if it did, . . . . Now that's funny! On a lot of different levels. I can see a lot of airhead riders going for free but horsepower? Their bikes won't go clickity clack, leak, smoke, and shudder side to side if they get much free horsepower. Their cat skull might fly off and they would need brakes! :rofl
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  20. wirewrkr

    wirewrkr the thread-killer

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    A new forum, a whole new audience...............
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