|
|
Thread Tools | Display Modes |
#181
|
|||
|
|||
Fork installation - How stupid is this hack?
On Aug 28, 12:28*am, jim beam wrote:
Frank Krygowski wrote: On Aug 25, 11:38 pm, jim beam wrote: Frank Krygowski wrote: IOW, the entire intake path is below atmospheric pressure. er, that's because of the carburettor restriction. No, "jim," it's because the pistons are moving downward while the intake valve is open. *The expansion in the volume of the cylinder plus intake path (manifold, carburetor/throttle body/etc, air cleaner, etc.) causes a drop in pressure. south of the valve restriction, that's true. *but since the manifold is bigger than the valve hole restriction[s], the vacuum in the manifold is due to throttle/carb venturi and the flow rate, not "vacuum from the piston". Wow. I thought you were a _little_ better at physics. Guess I was wrong. *Everything downstream from the air cleaner's intake horn is below atmospheric pressure. *That's what sucks the air into the engine. you'll have a hard time measuring any pressure drop on the far side of the throttle krygowski. * Your sniping would be more understandable if you would define your terms better. By "far side" did you mean "upstream"? Not that it matters much, of course. Almost everything you're writing shows tremendous ignorance of fluid mechanics. First, if your venturi is venting directly to atmospheric pressure, you will get the same effect, but only because the pressure immediately downstream of the throat is almost exactly atmospheric. If that pressure is sufficiently raised in any way (say, by a restriction) the venturi throat will be above atmospheric pressure. (See the robot gripper example below.) Bernoulli's equation is a conservation of energy equation for fluid traveling along a particular streamline. *For solid objects like swinging pendulum bobs, conservation of energy makes potential energy transform into kinetic energy and vice-versa. *For fluids in motion, the same principle makes an additional change: pressure changes. *But as with a swinging weight, the changes apply to the particular particles of fluid that are flowing, not to the ones outside the pipe. The reduced cross section area of a venturi's throat causes higher speed (more kinetic energy) in that section of the fluid stream. *This is balanced by having less "pressure energy" (so to speak) at the throat than immediately upstream or downstream. But is the throat's pressure guaranteed to be below atmospheric? Definitely not. but it /is/ guaranteed to be below input pressure. Correct, but not pertinent. If the pressure downstream of the venturi is, say, 100 psi, the venturi throat might be at 90 psi above atmospheric. Drilling a hole into the throat would result in fluid spraying out into the atmosphere. This will never happen with a carburetor because the entire intake passage is below atmosphric pressure. no it's not - only the section south of the venturi is below atmosphere. Absolutely, completely false. The flow of air in the intake passages of an engine is caused by pressure drop. The more restriction in a certain location, the larger the pressure drop required across that restriction. Air first enters the "air horn" portion of the air cleaner because pressure within the air horn is lower than atmospheric. Yes, even in the air horn, pressure is lower than atmospheric. Air flows through the filter element of the air cleaner because the pressure inside the air cleaner (downstream of the filter) is lower than the pressure in the air horn. This explanation continues all the way to the intake valve, where the pressure inside the cylinder is lower than the pressure just before the valve. This is true even in a diesel engine. Its intake passages are below atmospheric even though there is no venturi. The only important exception is an engine which is supercharged or turbocharged. But even there, pressure in the intake of the 'charger is lower than atmospheric. The 'charger pumps it up in order to increase the flow of air and fuel; but from there on, the pressure gradient is downhill, except for the two-inch expansion of the venturi (where fitted). In that section, flow is maintained by inertia, not pressure drop. So once again: Supercharging or turbocharging excepted, the entire intake passage, going all the way upstream to the air horn, is below atmospheric pressure. Otherwise flow would not occur. Once again, "jim," if you restricted your posts to what you actually know about, your posting volume would drop by over 90%. - Frank Krygowski |
Ads |
#182
|
|||
|
|||
Fork installation - How stupid is this hack?
In article
, Frank Krygowski wrote: The flow of air in the intake passages of an engine is caused by pressure drop. The more restriction in a certain location, the larger the pressure drop required across that restriction. Air first enters the "air horn" portion of the air cleaner because pressure within the air horn is lower than atmospheric. Yes, even in the air horn, pressure is lower than atmospheric. Air flows through the filter element of the air cleaner because the pressure inside the air cleaner (downstream of the filter) is lower than the pressure in the air horn. This explanation continues all the way to the intake valve, where the pressure inside the cylinder is lower than the pressure just before the valve. This is true even in a diesel engine. Its intake passages are below atmospheric even though there is no venturi. An internal combustion engine would be unable to operate if all those things were not true. The atomized fuel/air mixture would never get into the cylinder otherwise (slightly different in the case of fuel injected engines, which has a different mixing point for the fuel and air than a carbureted engine). The only important exception is an engine which is supercharged or turbocharged. But even there, pressure in the intake of the 'charger is lower than atmospheric. The 'charger pumps it up in order to increase the flow of air and fuel; but from there on, the pressure gradient is downhill, except for the two-inch expansion of the venturi (where fitted). In that section, flow is maintained by inertia, not pressure drop. So once again: Supercharging or turbocharging excepted, the entire intake passage, going all the way upstream to the air horn, is below atmospheric pressure. Otherwise flow would not occur. Once again, "jim," if you restricted your posts to what you actually know about, your posting volume would drop by over 90%. But what fun would that be, without "jim" tossing all those ducks in the barrel? He may be able to "do the math" but it's the fundamental understanding that eludes him. He re-enacts the "Ballad of Irving" in these threads every time: http://dmdb.org/lyrics/irving.html |
#183
|
|||
|
|||
Fork installation - How stupid is this hack?
On Aug 24, 2:33 pm, wrote:
On Sun, 24 Aug 2008 09:07:51 -0700, jim beam wrote: wrote: On Sat, 23 Aug 2008 20:39:27 -0700 (PDT), pm wrote: On Aug 23, 7:48?pm, wrote: On Sat, 23 Aug 2008 19:30:24 -0700 (PDT), pm wrote: http://groups.google.com/group/rec.b...e4627d53510adc Dear PM, Thanks for looking into things, but consider the results. First you had to decide to search for indexed + headset + crash. (There are, after all, quite a few other possibilities.) It was the first thing I typed in to Google. I did not consider any other possibilities. Perhaps you can consider some other possibilities, and report on the results? You can either find more incidents, or no more. And here's what that search finds: http://groups.google.com/group/rec.b...?group=rec.bic... You have to pick that example out of 19 hits, most of which seem to be about how the poster thinks that the indexing is _not_ related to the crash. I have to pick that example out of 1 hit. It is the first hit. There are, of course, some other hits relating to a post I made where I have bent fork and an indexed headset, with no crash. Of course I don't think my indexed headset is relate to a crash -- I didn't crash. If that's all that google will turn up, it's unimpressive. I don't actually care about whether headsets dent on impact. What's really unimpressive is that apparently grown men will spend hours shouting "but you need to do it!" at each other, when the task in question is something that takes all of 10 seconds. The situation is similar to someone implying that there are _lots_ of examples by telling everyone else to look them up. An extraordinarily fast way to refute such an implication is to actually attempt to look them up. -pm Dear PM, Actually, it's an extraordinarily _slow_ way to refute such things--proving a negative is darned hard. If Jim knows of such examples in the archives, he should find them and cite them. If he doesn't, there's no way for us to tell if he's dishonest, exaggerating, mistaken, bluffing, or just using a search string that no one else thought of. There are no black swans in my neck of the woods. I could search forever without finding any, but that doesn't refute their existence. You have to search for them in Australia. Cheers, Carl Fogel carl, with respect, i recall previous posts with exactly this corroboration from previous arguments on this subject, so i know they're there. whether i can be bothered to mess about searching for them, especially when the questioner is not only a google expert but apparently intent on just wasting electrons on b.s. black swan arguments, especially after pm's posts, is an entirely different matter. Dear Jim, So you can't be bothered to support your own claim and it's up to everyone else to do so? Okay, I'll make the obvious counter-claim. There are scarcely any such posts claiming impact damage in the archives, and the few that can be found by laborious searching are obviously vague, mistaken, and even dishonest. I can't be bothered to mess about searching for them. Last year I collided with a large tree-trunk, horizontal, at quite high speed after momentarily losing it during a singletrack descent. The wheel sustained no apparent damage. Fork sustained a slight bend. Headset was broken and ejected completely from the headtube, which was destroyed. Robert |
#185
|
|||
|
|||
Fork installation - How stupid is this hack?
Frank Krygowski wrote:
On Aug 28, 12:28�am, jim beam wrote: Frank Krygowski wrote: On Aug 25, 11:38 pm, jim beam wrote: Frank Krygowski wrote: IOW, the entire intake path is below atmospheric pressure. er, that's because of the carburettor restriction. No, "jim," it's because the pistons are moving downward while the intake valve is open. �The expansion in the volume of the cylinder plus intake path (manifold, carburetor/throttle body/etc, air cleaner, etc.) causes a drop in pressure. south of the valve restriction, that's true. �but since the manifold is bigger than the valve hole restriction[s], the vacuum in the manifold is due to throttle/carb venturi and the flow rate, not "vacuum from the piston". Wow. I thought you were a _little_ better at physics. Guess I was wrong. idiot. �Everything downstream from the air cleaner's intake horn is below atmospheric pressure. �That's what sucks the air into the engine. you'll have a hard time measuring any pressure drop on the far side of the throttle krygowski. � Your sniping would be more understandable if you would define your terms better. By "far side" did you mean "upstream"? idiot. Not that it matters much, of course. Almost everything you're writing shows tremendous ignorance of fluid mechanics. idiot. First, if your venturi is venting directly to atmospheric pressure, you will get the same effect, but only because the pressure immediately downstream of the throat is almost exactly atmospheric. If that pressure is sufficiently raised in any way (say, by a restriction) the venturi throat will be above atmospheric pressure. (See the robot gripper example below.) Bernoulli's equation is a conservation of energy equation for fluid traveling along a particular streamline. �For solid objects like swinging pendulum bobs, conservation of energy makes potential energy transform into kinetic energy and vice-versa. �For fluids in motion, the same principle makes an additional change: pressure changes. �But as with a swinging weight, the changes apply to the particular particles of fluid that are flowing, not to the ones outside the pipe. The reduced cross section area of a venturi's throat causes higher speed (more kinetic energy) in that section of the fluid stream. �This is balanced by having less "pressure energy" (so to speak) at the throat than immediately upstream or downstream. But is the throat's pressure guaranteed to be below atmospheric? Definitely not. but it /is/ guaranteed to be below input pressure. Correct, but not pertinent. no, correct and very pertinent. in fact, to ignore it is a fundamental mistake on your part. you can't just ignore facts just because they're inconvenient krygowski. If the pressure downstream of the venturi is, say, 100 psi, the venturi throat might be at 90 psi above atmospheric. Drilling a hole into the throat would result in fluid spraying out into the atmosphere. This will never happen with a carburetor because the entire intake passage is below atmosphric pressure. no it's not - only the section south of the venturi is below atmosphere. Absolutely, completely false. ok, let's clarify since you don't seem to be clear on the principles: only the section south of the venturi is significantly below atmosphere. the section north of it, for flow purposes, is completely negligible. The flow of air in the intake passages of an engine is caused by pressure drop. that much is true, but not pertinent or significant to pressure differentials. The more restriction in a certain location, the larger the pressure drop required across that restriction. duh. but not north of it. as above. Air first enters the "air horn" portion of the air cleaner because pressure within the air horn is lower than atmospheric. Yes, even in the air horn, pressure is lower than atmospheric. Air flows through the filter element of the air cleaner because the pressure inside the air cleaner (downstream of the filter) is lower than the pressure in the air horn. This explanation continues all the way to the intake valve, where the pressure inside the cylinder is lower than the pressure just before the valve. the biggest pressure drop in an intake, north of the throttle, is due to the filter, not simply the air duct. you don't seem to understand that. This is true even in a diesel engine. Its intake passages are below atmospheric even though there is no venturi. and the filter is /where/ exactly? The only important exception is an engine which is supercharged or turbocharged. But even there, pressure in the intake of the 'charger is lower than atmospheric. The 'charger pumps it up in order to increase the flow of air and fuel; but from there on, the pressure gradient is downhill, except for the two-inch expansion of the venturi (where fitted). two inch??? that's random crap from you having one specific example in mind, that's not evidencing a proper grasp of the general principles. In that section, flow is maintained by inertia, not pressure drop. so finally, we get to the subject that is /way/ more significant than your other bleatings. air has mass and therefore momentum. dynamic supercharging depends on it, and has the potential, get this, to pulse pressures from dynamic supercharging that can be considerably higher than atmospheric when an intake system is tuned right. So once again: Supercharging or turbocharging excepted, the entire intake passage, going all the way upstream to the air horn, is below atmospheric pressure. Otherwise flow would not occur. Once again, "jim," if you restricted your posts to what you actually know about, your posting volume would drop by over 90%. you're confused. in an intake system, the pressure drop north of a restriction is negligible because the restriction is the limiting factor, not the tube. restriction 1 - intake valves/head ports. restriction 2 - throttle body restriction 3 - filter. pressure differentials elsewhere in the system are negligible. fyi, when tuning cars, someone that knows their business is much more worried about flow dynamics than they are pressure differentials. for hondas, that's why people that spend money on enlarged port throttle bodies seldom show power increases on the dyno. because what matters is going on with the dynamics of the intake tubes south of there like intake tube resonance, valve restrictions, the dynamics of valve timing crossover, and of course, exhaust flow. like an intake tube, properly designed, an exhaust header can improve exhaust scavenging significantly, and tube diameter has much less to do with it than the dynamics of the flow path, contrary to your thinking. |
#186
|
|||
|
|||
Fork installation - How stupid is this hack?
On Aug 26, 5:57*pm, wrote:
[Discussion of forks that eventually wandered into headset pitting and indexing and something about the wind from passing trains and airfoils] I see we are stuck with selective citations from Bernoulli (Swiss) and Brinell (Sweden). *Those damn Italians mess up this newsgroup no end. Guys with names like that must have some Italian ancestry. If only Sheldon Brown were here, he might regale us with the tale of Bruno Brinelli, the little-known black-sheep cousin of Cino Cinelli. Bruno Brinelli's great innovation in the Italian bicycle industry was to introduce the indexed bottom bracket, which promised to modify the rider's pedal stroke, accelerating and retarding it so as to eliminate the dreaded "dead spot" in the pedal cycle. Now you wouldn't have to be Coppi or Bartali to "pedal circles"! Sadly, Brinelli's breakthrough was compromised by his insistence on using the Canadian bottom bracket standard, with French threading a la droite and English threading on the left. He fretted over such indignities for several years, until, disillusioned by the failure of the traditionalist Italian industry to take up his lead, he left to seek his fortune in the Far East. Here the chronicles become hazy. It is thought that, years later and under a different name, Brinelli-san was behind Shimano's introduction of Biopace chainrings, which the cognoscenti have always known may be pronounced "Bio-pa-chay" in true Italian style. But alas, Sheldon is not here, so I fear we will never hear of the further innovations of Bruno Brinelli. Ben Weiner |
#187
|
|||
|
|||
Fork installation - How stupid is this hack?
|
#188
|
|||
|
|||
Fork installation - How stupid is this hack?
On Aug 29, 12:16*am, jim beam wrote:
Frank Krygowski wrote: On Aug 28, 12:28 am, jim beam wrote: Frank Krygowski wrote: This will never happen with a carburetor because the entire intake passage is below atmosphric pressure. no it's not - only the section south of the venturi is below atmosphere. Absolutely, completely false. ok, let's clarify since you don't seem to be clear on the principles: only the section south of the venturi is significantly below atmosphere. * the section north of it, for flow purposes, is completely negligible. :-) Hilarious! The section upstream of the venturi is negligible ONLY if you don't want air to flow into your engine! But if you DO want any air flow into your engine, its intake passages, starting at the air horn, will have to be below atmospheric. (Unless you've got a supercharger or turbocharger, as I previously said.) If intake is not below atmospheric, there's nothing to cause air to be sucked into the air horn, air cleaner, etc. So your unqualified statement, "only the section south of the venturi is below atmosphere," is absolutely, totally, flat wrong. And your current attempt to fudge in the word "negligible" is flat wrong, too. "jim beam," why not just restrict your posts to things you actually know about? Think of the time you'd save! - Frank Krygowski |
#189
|
|||
|
|||
Fork installation - How stupid is this hack?
On 2008-08-29, Frank Krygowski wrote:
On Aug 29, 12:16*am, jim beam wrote: Frank Krygowski wrote: On Aug 28, 12:28 am, jim beam wrote: Frank Krygowski wrote: This will never happen with a carburetor because the entire intake passage is below atmosphric pressure. no it's not - only the section south of the venturi is below atmosphere. Absolutely, completely false. ok, let's clarify since you don't seem to be clear on the principles: only the section south of the venturi is significantly below atmosphere. * the section north of it, for flow purposes, is completely negligible. :-) Hilarious! The section upstream of the venturi is negligible ONLY if you don't want air to flow into your engine! But if you DO want any air flow into your engine, its intake passages, starting at the air horn, will have to be below atmospheric. (Unless you've got a supercharger or turbocharger, as I previously said.) If intake is not below atmospheric, there's nothing to cause air to be sucked into the air horn, air cleaner, etc. Well it could just be pushed in by your foward speed. In other words, pressure in the horn could be atmospheric, but greater than atmospheric just in front of it because of the "headwind" due to your forward speed. So air would get pushed in. People have used funnel-shaped forward-facing intakes to get that effect, which is like a mild supercharger. Of course that isn't the only way to get air in or you wouldn't be able to start the engine while stationary for one thing. |
#190
|
|||
|
|||
Fork installation - How stupid is this hack?
On Aug 29, 1:02*pm, Ben C wrote:
But if you DO want any air flow into your engine, its intake passages, starting at the air horn, will have to be below atmospheric. *(Unless you've got a supercharger or turbocharger, as I previously said.) *If intake is not below atmospheric, there's nothing to cause air to be sucked into the air horn, air cleaner, etc. Well it could just be pushed in by your foward speed. Not in real life, Ben. (Although I realize you're just trying to cover every wildly hypothetical case.) In other words, pressure in the horn could be atmospheric, but greater than atmospheric just in front of it because of the "headwind" due to your forward speed. So air would get pushed in. Practically speaking, you might use that to get a little air to flow into the air horn. But the next restriction is the air filter. Can you imagine the size of the air scoop, and the speed of the vehicle, necessary to get an engine's air flow rate through the air filter? We're not talking about ramjets, after all! People have used funnel-shaped forward-facing intakes to get that effect, which is like a mild supercharger. People have done all sorts of strange and unproductive things, laboring under beamish misconceptions. Such forward facing scoops consume more power by aero drag than they add by "mild supercharger" effect. This is the reason NACA ducts were invented. See http://en.wikipedia.org/wiki/NACA_duct Of course that isn't the only way to get air in or you wouldn't be able to start the engine while stationary for one thing. Indeed. - Frank Krygowski |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Stupid Americans! -- Stupid... Stupid... STUPID!!! ___________ ylojceq | Tom Kunich | Rides | 672 | December 3rd 04 07:49 AM |
Stupid Americans! -- Stupid... Stupid... STUPID!!! ___________ | David Reuteler | General | 0 | November 11th 04 07:41 PM |
Stupid Americans! -- Stupid... Stupid... STUPID!!! _____________ vyphih | Hunrobe | General | 11 | November 11th 04 03:45 AM |
Stupid Americans! -- Stupid... Stupid... STUPID!!! ___________ ylojceq | Tom Kunich | Rides | 4 | November 10th 04 05:26 AM |
Stupid Americans! -- Stupid... Stupid... STUPID!!! ___________ ylojceq | Tom Kunich | Social Issues | 2 | November 10th 04 05:26 AM |