airbox mods

[milkman]

Morning all.
Well, I was looking through the forum past threads and couldn't find anything on this topic, so often a large one on other bike forums.

What airbox mods has anyone tried, liked, hated etc etc.
I realise a majority of you are in areas where it gets quite cold so you proabably keep teh box relatively stock for easier cold starting, maybe just put a K&N filter in?

Anyone tried removing the inlet hoses in the box, or widening the inlet hoses under the tank, or repostionig them. I would like to try extending them with a larger bell mouth inlet to just outside the tank, just to ram some more air inthere.
 
Anyone liked the small pods directly on the carbs?

I realise there are only small gains to be made, but gains none teh less in power, smoothness and feul economy.

If this is listed somewhere else and I couldn't see it, just point me there.

Thanks

[Jon_P]

i have heard abou drilling holes in the stock air box. i was kind of wondering myself. i had wondered about the air pods, when i got mine it didnt have a airbox, i was told by enough people not to do the pods because i would gain some in the upper end yet lose it in the lower and mid of the throttle. can say its true cuz i never tried. also was told that ya have to tune the carbs contiuneously depending on the weather?

[Ed Miller]

http://home.jps.net/~snowbum/R80,%201980+,%20Airboxmods.htm

I bought a bunch of airbox parts off Ebay some time back, so I could have spare emissions stuff, and it came with an airbox that had snorkles of two different sizes, so I put that on.  I couldn't tell any difference.

[milkman]

It has definitely made a difference on other bikes I've had, particularly smoothing out throttle response. If you couple it with free breathing pipes, you do need to fiddle with your jets sometimes as the increase in air can lean you fuel mixture out, but maybe BMW (or Beemer people) are different? MAybe the practicality of the german engineering isn't benefited like the old british bikes I've had? Still going to have a play though....

[Rob Valdez 79 R65]

You might try the older "clamshell" type airbox that uses a round air filter.  Some have the rear drilled with holes and some do not.

My bike, being a '79 US model, was the last year for the clamshell in this country.  It DID come with a drilled airbox from the factory.  Some say this drilling makes the intake noiser.  It never bothered me.

While the individual "pod" filters look cool and can lead to some interesting café stylings, I hear nothing but bad things about them from the elders.  The two biggest drawbacks are increased dirt-flow, and sucking in water in the rain.

I don't see any reason to use a K&N filter in the stock airbox, either.

These bikes run fine with the stock airbox and filter, which ever style.  If you are trying to get the bike to run right by changing these, something more serious is wrong, and should be corrected.

[Semper Gumby]

I have the K&N aitr filter and it works fine and I don't have to buy filters anymore.  I also remove the air injection system to get rid of the popping sound. (It worked)  

I see no need or reason to further modify the air induction system.  If I install a Hannigan fairing on then I might consider some cold air hoses leading to the intakes.  Right now my R65 works really well.  Why mess with a good thing? 8-)

[Scout39]

Something I learned from my engine tweaking experiences is that the air in your intake system has inertia -  several engineers have worked with intake tracts which vary in length in response to engine rpm to take advantage of this effect. I found that the K&N "pod" type air filters provided little gain unless the original intake system was hopelessly inadequate to begin with. When I punched out my Sportster (yes, as in Harley Davidson) I kept the original 883 heads and carb since the smaller valves and intake tract create higher velocity flow at low-to-mid rpm, effectively packing more mixture into the cylinders. Above 5,000 rpm a stock 1200cc Sportster will start to pull away but, below that, where most of us ride, the smaller-valved version is a torque monster and much zippier to ride. These days, I look for a rideable powerband though it's always fun to look for those "hidden" horses.

My other "new" bike is an '82 R65 - go figure. The only commonality is that I've found that some Beemer riders consider the R65 to be not quite a "real" BMW and HD riders openly deride the Sportster as a "girls" bike. Oh yeah, and they're both black - the proper color for motorcycles.

[Rob Valdez 79 R65]

My Sportster of yesteryear:




I like yours!

[Scout39]

nice Sporty - looks like you used those flat Holland bars I also have... good color too!

[ignatz]

I did the individual K&N's back in 81 on my 79R65 because I felt my bike needed more air. They look and sound great, but are not practical for an everyday rider. While sitting at a traffic light in the pouring rain I went to pull out when the light turned green. The left carb coughed (cause the K&N was soaked) and the carb popped off and was hanging by the cables. I reached down, stuck it back on, and fired it back up with more throttle. It was so cool! I did't have much further to go to work and I was laughing all the way. I then added more holes to my clam-shell air box case and use only stock air filters. I feel my air filters need replacement often, not so much as road dirt gets in, but oil vapor from the breather mists the inside of the filter and restricts the air from coming in. When my idle gets low, I change the air filter..(and they don't look that bad) but then it runs better. My Ducati is the same way...Low idle=new Stock air filter.

[Scout39]

Now THAT is a good story!!!

[Rob Valdez 79 R65]

(snip) I feel my air filters need replacement often, not so much as road dirt gets in, but oil vapor from the breather mists the inside of the filter and restricts the air from coming in.

I rerouted my crankcase breather a long time ago.  But it wasn't until Spring of '06 that I cleaned it up and did it right.
http://www.pbase.com/tomfarr/crankcase_breather

[Justin B.]

I've stayed out of this one as I really don't have any first-hand information with Beemers.  The only bike I've ever owned that was set up like this was my old 450 Honda and I ran it with just velocity stacks with a fine screen.  The 450 had been so modded I really couldn't make any kind of objective guess as to how they affected it.

I had thought of playing with the dual K&Ns on one of the Beemers but it seems everything I read indicates BMW pretty much got it right concerning the intake and exhaust systems, and for streetability it's best to leave them alone.  All I have done is replace the paper elements with K&N elements (on our three riders) and can't really say I have noticed any difference one way or the other.

General observations lead me to believe that about the best that could be done (keeping street riding in mind) would be to maybe modify the inlet snorkels/holes and figure out a way to get cooler air into the airbox as milkman is contemplating.  There's a rule of thumb equating amount of power increase vs lowering the inlet charge by a certain number of degrees but I can't remember what it is except that a cooler intake temp DOES increase HP.  I have personally seen timeslips showing a small ET reduction on V8 hotrods at the strip after the intake manifold was iced down.  Something else that my instincts tell me would be a good thing would be to get the crankcase breather tubes out of the airstream, surely this must introduce a lot of turbulence that I have always heard is undesirable upstream of the carbs...

[Rob Valdez 79 R65]

The guys here at Indy pray for cool weather on the first day (pole position) of qualifications for the 500.
They definitely run faster.  Chemistry on the molecular level, I believe.  

[Jon_P]

thanks for the link for thecrank case breather mod Rob! going to add that to my salvage build!

i have run pods on other bikes. a 4 cylinder never seems to work because the air difference between the inner cylinders compared to the outer cylinders never worked out, always had one running lean it seemed. on the brit twins and a xs650 twin the pods worked nice except when a large truck would pass and create a low pressure on that side of the bike and it would run lean for a second or two. but other than that they worked ok, i should also say the exhaust was modified for increase flow on those bikes also.

i also like the older clam shell air box because it flows with the engine. i love that look, i feel it is the cleanest factory air box set up ever. even though i am building a cafe/street fighter look i will leave the stock air box and exhaust.