Both of my 1984 R100's have 2 large snorkels, both have 40mm Bings, both have large valve heads, and both were delivered with 8.2:1 pistons, which I have recently replaced with 9.5:1. My understanding is that BMW moved to the asymmetrical snorkel arrangement sometime around late 1983 production, and they did it to move the torque curve to the midrange area of the powerband, but the upper RPM range flattened. I'm curious to know if this was a US-only specification, done perhaps to improve rideability that might have suffered from the leaner jetting specification, or if 1984 model year 9.5:1 CR bikes delivered to the rest of the world also had the asymmetrical arrangement? Does the one small snorkel still detract from the upper RPM performance of these 9.5 engines?
I can’t notice much/any difference with or without snorkels on my ‘81 RS. And it gets revved to the top floor.
I never noticed any difference in power with snorkels on or off...in any combination. But on my 400km weekly commute at the time, what I did notice was fuel economy - you sure notice a 20km drop in range to reserve. Better fuel economy without snorkels. My R65 Mono has the torque dip between 4,000 and 5,000 rpm...what I suspected and later confirmed on the dyno, I have shifted the dip out of my cruising speed, giving better fuel economy. Snorkels were just one of my experiments. And I have them on at the moment, fuel economy not being a concern these days.
I know from a service bulletin that they replaced one of the snorkels on European R65's and did some re-jetting to make them run right. This was done mid 82. The way I read it, this is a tuned intake system and they didn't get it quite right when the flat airbox and snorkels were introduced in 81. Hard to believe a dyno wouldn't show some impact of the snorkels being removed otherwise why did BMW fit them.
This is a big part of the reason. If they lesson the intake noise it gives them more room for fin noise and exhaust.
I like that Amazon auto-loaded an ad for this on this thread. Those know-it-all robots need to work a little bit harder.
Here are some torque curves from Moorespeed advocating for their pistons and airbox (with no snorkels). I suppose this has been gone over before, but I find it interesting. (Yes, I know giving too much weight to HP curves provided by manufacturers is perhaps not always wise.) The green run is a stock R100 with the stock square airbox and snorkels. The maroon curve is stock airbox with Moorespeed long skirt pistons. Pretty much the same curve with a slight shift. Maybe a bit more than slight. The blue curve is the same configuration as the maroon—but for the switch from stock airbox to the open Moorespeed box. Bit of a difference. Above 3500 and it's all looking good for Moorespeed, but the low end is not only "less good"—it could be interpreted by some riders as really bad. Torque is in a hole at 2500, then comes on in a rush. I think the BMW philosophy was to value the more gradual buildup to peak torque. Call it low end tractability, or something like that. And it's a very reasonable approach, no? That's what the snorkels give you, I guess, in addition to what surely was required as intake silencers. And here is the Moorespeed airbox.
I ride the bike at 2500 about every 100 yards. Nothing drives me crazier than a bike that's lazy off a stop light.
If you look at the parts diagram, the tuned length for the intake tract is done with parts #12 & #13. The snorkels being discussed here (#1) are purely for intake noise reduction.
Snorkels were used on car airfilters for decades, they were always called air silencers. These days they use Helmholtz chambers and stuff to cut intake noise. That's the snorkel function on an Airhead airbox, to read anymore into it is just fake news.
Assuming that they are strictly for intake noise reduction, why would BMW modify the design, making one smaller than the other? It's the decision to go asymmetrical that has me scratching my head.
Tighten a loose fit between snorkel and air-box, wind monofilament fishing line into the groove at their joint. - read on 'net, works.
From the few times I have run CV carbs on the dyno, ( because they are junk) the 2500rpm dip is due to the throttle butterfly being open fully, and the slide faltering before I opens in true CV form. CV carbs also exhibit a natural accelerator pump function due to the slide opening slowly whilst the airspeed under the slide has increased. The 2500rpm dip could be either or both of these. I would like to see the dyno run again with slide carbs ( preferably small diameter TM Mikunis) or with well jetted accelerator pumps ( tiny pump nozzle) OR the stock 32mm carbs which will open much faster not everything is what you think on a dyno sheet. We ran HD Evo engines on the dyno hundreds of times, the dip from the initial "snatch" was similar on Evo 80 with Mikuni HS/HSR carbs, the engine would also spit, as though it was running weak. It turned out (after we stuck a Lambda probe in a drilling near the exhaust port that it wasn't weak it was RICH.) we reduced the accelerator pump nozzle to the smallest and it picked up much better... no dip
One mans junk is anothers' jewel.The CV is reliable, economical, robust, long lived. They self adjust for altitude changes. They will run on bad gas that will stop a Mikuni.This makes them popular with the small aircraft crowd. They are laggy compared to a slide (or pure butterfly) throttle carb so they do best in constant throttle applications, like small aircraft and touring motorcycles. if you are running torque curves on an airhead methinks you are missing the point of the machine.
"They will run on bad gas that will stop a Mikuni" Plaka, you are displaying your ignorance with that one. Explain how that works.
I think that the engineers discovered the one part on an airhead that WASN'T asymmetrical and had to fix it.
"They will run on bad gas that will stop a Mikuni" a carburettor is a fuel metering device, the better the carb the better it will meter the fuel. I struggle to see how a Mikuni will falter, where a Bing wont. Please quantify the phrase " bad gas", low octane, full of water, dust dirt, bad as in naughty ? Bing were used by BMW because they were cheap, and of course pure nepotism as they were German, Bings were a fine carb in around 1953, but then the japs arrived with proper carburettors and the rest is history, anyone who truly believes that a Bing is better carburettor ( from an objective standpoint) than a Mikuni is just in denial. Peculiar isn't it, that when you change the Bing for Mikuni the bike livens up, revs better, drinks less fuel, creates more torque, weighs around 30lbs less ( Bing boat anchor) However if you are happy with your Bing, then that is fine, but please don't " big up" what is a fairly mediocre instrument at best.
maybe the different snorkel lengths was to silence different frequencies. one thing is for sure they are noise suppression devices. I am just increasing the volume of the airbox with a 34mm high aluminium "band" welded on top of the OEM late model airbox. anyone any experience of this ?
