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Old 10-09-2011, 10:06 PM   #55336
Aerocycle
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Originally Posted by Biker Buzz View Post
Ok. I just bought a new 2011 DR650 this weekend. While checking out different postings on this much exhaused subject, I have a theory...like everyone else. At the risk of beating a dead horse here's my take on the subject.

Makes sense, huh?

What do you think?

However, I do think the shape of the snorkel is helpful in keeping debris/water out of the airbox.
I see you've smelt the coffee brewing...

DR650 + cut air box + TM40 carb + K&N + New Exhaust + $800 = Suck, Squish, Bang, Blow.... Faster in/Faster out, more power to ya....
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Old 10-09-2011, 10:20 PM   #55337
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Originally Posted by Aerocycle View Post
I see you've smelt the coffee brewing...

DR650 + cut air box + TM40 carb + K&N + New Exhaust + $800 = Suck, Squish, Bang, Blow.... Faster in/Faster out, more power to ya....

That is the way it works!
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Old 10-09-2011, 10:20 PM   #55338
doug s.
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Originally Posted by Biker Buzz View Post
Nope. Not more air...faster air. Volume is not increased... but velocity is increased. The restriction, as you mentioned, is not the size of the snorkel, it's the shape of the snorkel. Volume remains the same. (If the inside diameter of snorkel is same as hole in which snorkel is inserted...or close in size.)
nope, not faster air - MORE air. even if the opening is the same size, the snorkel is still a restriction, letting less air in. prolly is putting the airbox into a slightly negative pressure situation. less air is being pulled in w/the snorkel. cut open the air box, and you will let even more air in.

actually, w/the snorkel, the air in that situation is likely moving faster - yust not as much of it. making air travel further, which the snorkel does, makes it move faster. yust like making air travel faster over the longer dimension of the top of an airplane wing vs the shorter distance it travels under the wing, which provides the lift. but in the case of an airplane wing, it IS faster air, not more air, cuz there's no restriction - the wing is out in the open.

because the snorkel puts bends in the path of the air, the air is traveling faster than w/o it. unfortunately, it's also restricting the quantity of air. which is why removing it, and cutting a hole in the airbox means you will likely have to re-jet so you won't run too lean - MORE AIR not "faster air".

actually, there will be faster air going thru the carb itself, if there's more air, cuz the carb itself is a specific size. when it moves more air, it has to also be faster.

doug s.

doug s. screwed with this post 10-09-2011 at 10:24 PM Reason: clarification
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Old 10-09-2011, 10:44 PM   #55339
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Originally Posted by motolab View Post
...As long as you don't mind replacing the parts a bit more often.

See:
Slide guide, used
Slide guide, new
Slides, new and used
Emulsion tubes, new and used
Jet needles, new and used

Scroll down for description and links. Click image for high-res view.

Consider that there is an intake pulse every 720 degrees, which is what raises the slide. Between those pulses, the slide spring and gravity try to push the slide back down. In order for the slide to be allowed to be pushed back down, the vacuum above diaphragm has to bleed off through the slide lift holes. The larger the slide lift holes, the faster that vacuum can bleed off, and therefore the greater the distance the slide can be pushed down before the next pulse. At the next pulse, the slide has to be pulled back up by the distance it fell (more if there is acceleration, less if there is deceleration). Conversely, the smaller the lift holes, the slower the vacuum can bleed off, and therefore the smaller the distance the slide can be pushed down before the next pulse, and therefore the smaller the distance the slide has to be pulled back up at the next pulse.

My opinion is that the perceived benefits of slide drilling may be at least somewhat related to resultant changes in fuel metering rather than to the speed at which the slide is allowed to move, in which case one should instead concentrate on achieving the correct float height, pilot jet, needle profile and clip position. Then most if not all of the benefits could be achieved without additional wear on a carburetor that is already chronically wear prone.

Regards,

Derek
Excellent stuff Derek. I hope anyone who ever wants to have a clue about what really is going on in a carb is paying attention. It's complicated ... and
every change affects something else ... but your explanations and clear and precise.

PLUS ONE on the wear prone reference regards the BST40. I'm on my 2nd carb due to slide and jet needle wear ... which was causing a stumble off idle. Instead of pulling the old carb apart & buying very expensive stock parts ... I simply bought a nice near new used DR650 Carb for $60. Installed my jetting and DJ needle into it ... All good. The first carb went 30,000 miles before showing wear and affecting running very slightly.
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Old 10-09-2011, 11:13 PM   #55340
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Quote:
Originally Posted by doug s. View Post
nope, not faster air - MORE air. even if the opening is the same size, the snorkel is still a restriction, letting less air in. prolly is putting the airbox into a slightly negative pressure situation. less air is being pulled in w/the snorkel. cut open the air box, and you will let even more air in.

actually, w/the snorkel, the air in that situation is likely moving faster - yust not as much of it. making air travel further, which the snorkel does, makes it move faster. yust like making air travel faster over the longer dimension of the top of an airplane wing vs the shorter distance it travels under the wing, which provides the lift. but in the case of an airplane wing, it IS faster air, not more air, cuz there's no restriction - the wing is out in the open.

because the snorkel puts bends in the path of the air, the air is traveling faster than w/o it. unfortunately, it's also restricting the quantity of air. which is why removing it, and cutting a hole in the airbox means you will likely have to re-jet so you won't run too lean - MORE AIR not "faster air".

doug s.
The Size of the snorkel determines its volume...not its shape! For instance: A 1"x12" pipe bent in an "S" shape will have the exact same volume as a 1"x12" pipe that is straight. In other words, 12" is 12"...doesn't matter what shape it is. Which weighs more? A ton of feathers or a ton of rocks? See what I mean? Even if you took the airbox off completely and ran the engine, the lean/rich mixture wouldn't change. It would get the air in and out easier because of less restriction. That's why people use K&N filters and free flowing mufflers. Easier in and out.

"because the snorkel puts bends in the path of the air, the air is traveling faster than w/o it. unfortunately, it's also restricting the quantity of air."

How can it restrict the volume of air when the snorkel diameter is the same as the size of hole left after removing it? (pretty close in size, anyway.) I didn't mention anything about cutting another hole in the airbox.

I think by merely removing the snorkel it wouldn't have any significant change in the air/fuel mixture ratio. The hole in the box is pretty close to the size of the snorkel. I agree that the snorkel will restrict the velocity of air.

That's why building codes only allow so many bends in pipes, ducts, etc..in a given length. Bends restrict velocity of flow...not volume.
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Biker Buzz screwed with this post 10-09-2011 at 11:19 PM Reason: typo
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Old 10-09-2011, 11:45 PM   #55341
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Originally Posted by Biker Buzz View Post
The Size of the snorkel determines its volume...not its shape! For instance: A 1"x12" pipe bent in an "S" shape will have the exact same volume as a 1"x12" pipe that is straight. In other words, 12" is 12"...doesn't matter what shape it is. Which weighs more? A ton of feathers or a ton of rocks? See what I mean? Even if you took the airbox off completely and ran the engine, the lean/rich mixture wouldn't change. It would get the air in and out easier because of less restriction. That's why people use K&N filters and free flowing mufflers. Easier in and out.

"because the snorkel puts bends in the path of the air, the air is traveling faster than w/o it. unfortunately, it's also restricting the quantity of air."

How can it restrict the volume of air when the snorkel diameter is the same as the size of hole left after removing it? (pretty close in size, anyway.) I didn't mention anything about cutting another hole in the airbox.

I think by merely removing the snorkel it wouldn't have any significant change in the air/fuel mixture ratio. The hole in the box is pretty close to the size of the snorkel. I agree that the snorkel will restrict the velocity of air.

That's why building codes only allow so many bends in pipes, ducts, etc..in a given length. Bends restrict velocity of flow...not volume.
Try sucking through a long drinking straw and then cut a short piece of and suck through that. It's harder for the motor to suck air through the snorkel so it needs a bigger pressure differential, so there has to be a lower pressure in the air box. So although the volume of the air box remains the same, there is less air in it.
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Old 10-10-2011, 12:25 AM   #55342
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This thread SUCKS
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Old 10-10-2011, 01:17 AM   #55343
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Question side cover protectors

hi guys... where do you get the stick on side cover (case) protectors?

search seems reluctantat the moment...

cheers fish.
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Old 10-10-2011, 02:13 AM   #55344
NordieBoy
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Quote:
Originally Posted by Biker Buzz View Post
Nope. Not more air...faster air. Volume is not increased... but velocity is increased. The restriction, as you mentioned, is not the size of the snorkel, it's the shape of the snorkel. Volume remains the same. (If the inside diameter of snorkel is same as hole in which snorkel is inserted...or close in size.)
The only way to increase velocity without increasing volume/cfm is to restrict the aperture.
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Old 10-10-2011, 03:39 AM   #55345
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Quote:
Originally Posted by fishbulb View Post
hi guys... where do you get the stick on side cover (case) protectors?

search seems reluctantat the moment...

cheers fish.
procycle
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Old 10-10-2011, 03:53 AM   #55346
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Bikerbuzz.... it is more air. It is the same volume but it is more air. Confused yet. Air is a compressible substance so anything you do to restrict its flow causes a loss of pressure which means less molecules are present in the same volume. Bikes that have major modifications to exhaust or intake without changing the jetting typically run very badly because the air fuel ratio is way off.

PV=nRT is the ideal gas law which isn't strictly applicable here but it may help. P= pressure, V= volume, n = mass, R=universal gas constant, and T = temp. Ever notice your bike run differently when it's cold. Cold air is more dense given the same mass, pressure and volume (atmospheric pressure is fairly constant, but is affected by elevation and to a lesser extent weather). If you have the same volume and same temperature but less pressure you also have less mass to make the equation balance.
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Old 10-10-2011, 04:36 AM   #55347
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Originally Posted by Biker Buzz View Post
Makes sense, huh?
What do you think?
It's a helmholz resonator. The tube and box work in conjunction with one another to solve whatever problem the designer had in mind. In this case, it may have been to get the motor to run lean enough at one RPM range to allow it to pass an EPA test cycle. It may have been to get the airbox to be quiet enough to pass some test. It apparently wasn't designed to increase power.

From the Wikipedia:

It can be shown[2] that the resonant angular frequency is given by:
(rad/s),
where:
  • γ (gamma) is the adiabatic index or ratio of specific heats. This value is usually 1.4 for air and diatomic gases.
  • A is the cross-sectional area of the neck
  • m is the mass in the neck
  • P0 is the static pressure in the cavity
  • V0 is the static volume of the cavity
For cylindrical or rectangular necks, we have
,
where:
  • L is the length of the neck
  • Vn is the volume of air in the neck
(Boring density stuff deleted for brevity....)

thus, the frequency of the resonance is:
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Old 10-10-2011, 04:58 AM   #55348
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Quote:
Originally Posted by fishbulb View Post
hi guys... where do you get the stick on side cover (case) protectors?

search seems reluctantat the moment...

cheers fish.
Bad form to quote myself, but...

Quote:
Originally Posted by jon_l View Post
Might be prudent to add case savers. These should help in case of a tip over. They install in 10 minutes with a heavy bed (cushion) of hi-temp silicone (clean and degrease with isopropyl alcohol first).

http://www.procycle.us/bikepages/dr650.html



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Old 10-10-2011, 06:05 AM   #55349
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Quote:
Originally Posted by Biker Buzz View Post
Ok. I just bought a new 2011 DR650 this weekend. While checking out different postings on this much exhaused subject, I have a theory...like everyone else. At the risk of beating a dead horse here's my take on the subject.
-------------------------------------------------------------------------------------------------------------------------------------------------------------
Just by simply removing the snorkel you will not make the bike run leaner, you'll will get the air in faster (because the 45 degree bend has been straightened out, so to speak.). And after changing to a less restrictive muffler, you'll get the air out faster, which equals better performance because... (going back to my original statement) engines are basically just air pumps...they take it in and push it out.

Look at it this way; you can only cram so much air through the carburetors jets, venturis, orifices, etc. . The reason the have a particular size air box is to have a particular size filter necessary to do the job. You can remove the air box/filter assembly all together and the only thing that would change would be the ability to FLOW air more efficiently, not flow MORE air efficiently...not increased volume...increased velocity. Makes sense, huh?
What do you think?

However, I do think the shape of the snorkel is helpful in keeping debris/water out of the airbox.
First, Congrats on the new bike!
I won't even attempt explaining carb theory (probabaly better for all), But I will tell you that opening up the air box and exhaust will result in a lean condition. You may get away with pulling the snorkel, depending on your altitude, but anything much more will result in a lean conditon. In fact on the DR the change can be rather dramatic. My own experience with jetting and opening up the air box hole resulted in some pretty wild swings until I got the jetting and new hole size to match up.

But feel free to experiment away, the simplicity of the DR kind of encourages it. Good luck!
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Old 10-10-2011, 06:28 AM   #55350
doug s.
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Try sucking through a long drinking straw and then cut a short piece of and suck through that. It's harder for the motor to suck air through the snorkel so it needs a bigger pressure differential, so there has to be a lower pressure in the air box. So although the volume of the air box remains the same, there is less air in it.
thank you!

doug s.
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