Page 1176 of 2209 FirstFirst ... 1766761076112611661174117511761177117811861226127616762176 ... LastLast
Results 17,626 to 17,640 of 33122

Thread: ESE's works engine tuner

  1. #17626
    Join Date
    8th February 2007 - 20:42
    Bike
    TZ400
    Location
    tAURANGA
    Posts
    3,097
    Ah, sorry Frits, yes I misunderstood simply jumping to the comment about the extra end gases causing deto.
    Ring tension in the bore is a factor that can be spec'd when the rings are made, but it usually involves huge quantities for anything special..
    54 bore is super common, so I assume Wossner had access to these from their normal supplier already.
    The VHM setup uses a flat top piston, and makes better power, but in my experience the flat top only makes better power when combined with
    a full toroidal chamber, with the plug pulled down close into the middle of the combustion space.
    This cant be done in KZ2 as its then near on impossible to measure the assembled chamber cc to the regulations, so maybe the radiused timing edge itself is making
    the whole difference - not the combination with the flat top, will have to test and see.
    Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.

  2. #17627
    Join Date
    20th January 2010 - 14:41
    Bike
    husaberg
    Location
    The Wild Wild West
    Posts
    9,934
    DETONATION vs PRE-IGNITION


    DETO!
    By Kevin Cameron The Cellar Dweller

    I first encountered detonation back in 1966, and I didn't know what it was. Fortunately for me, it was a light case, and the only symptoms were small holes being eaten into the edges of a motorcycle cylinder head's squish band.

    Later, pushing to higher compression, I would generate my share of pistons that were detonated away until their rings hung out into empty space. I would learn to look out for the tiny, ash gray flake of quenched aluminum on a spark plug, or in water-cooled engines, for the sudden and otherwise unexplained rise in engine temperature. And I would still be curious about those dusty holes, eroded into cylinder heads.

    Books will tell you what Harry Ricardo learned back in 1918; that detonation is not the same as preignition. Preignition is lighting of the charge before the spark , by some hot object in the combustion chamber usually the overheated center wire of a spark plug whose heat range was too hot for the application. Preignition soon provokes detonation, so the confusion is understandable.

    Detonation, by contrast, is self ignition of some of the last parts of the charge to burn the so-called "end gas" out at the edges of the combustion chamber after the spark has already ignited and mostly burned the charge. This self igniting endgas does not then burn normally, as a flame front spread by turbulence at the usual speed of a few tens of feet per second. This gas burns at the local speed of sound, which is very high because the temperature is high. This form of combustion, called detonation, forms a shock front, a sudden jump in pressure that propagates at thousands of feet per second.

    When it hits parts, it hits hard. If we hear it al all, it is as a high, dry, irregular clicking, not unlike the reverberating sound of rocks struck under water. Detonation's pressure front can damage bearings by its hammering shock, but the real problem is what it does to an engine's natural, internal insulation.

    In any situation in which gases move next to solid surfaces, there is a layer of significant thickness that remains largely stagnant because it is attached to the surface. In internal combustion engines, this boundary layer quite effectively shields the engine's metal internal surfaces from direct contact with combustion gas, keeping them cooler than they would otherwise be.

    When detonation begins even light deto this boundary layer is scoured off by the impacting shock waves, and heat transfer from hot gas to cool metal accelerates. In only a very few detonating cycles, piston temperatures rise dramatically, and the rest of the parts exposed to combustion gas aren't far behind.

    What is strange to many people is that as this happens, exhaust gas temperature falls. This seems odd because people associate detonation with heat, and heat with failure. But the fact is that as you jet an engine down, its exhaust temperatures peak, not when the mixture becomes lean (that is, too little fuel to react with all the oxygen in the air charge), but when the mixture is chemically perfect. Exhaust gas temperature falls when detonation begins because the engine's internal insulation is destroyed; that being so, some heat that would otherwise go out the exhaust is now being diverted into the piston, head, and cylinder walls. Because those parts are getting hotter, the exhaust gas becomes colder.

    Those of us who began racing before water cooling arrived tend to think that engines get hotter the more we jet them down. With air cooling, this seems to be true, but isn't. The engine runs cool when it's rich because the extra fuel reduces peak flame temperature, and as we jet down towards chemically correct mixture, the engine runs hotter and hotter. Often, in a modified engine with high compression, this detonation begins even before we reach correct mixture and peak flame temperature. Then the engine really heats up. This leaves us with the idea that leaning down the mixture raises engine temperature, in a straightline relationship.

    Now we know, from our experiences with water-cooled engines, that power, engine temperature, and exhaust gas temperature all rise as we jet down until we go beyond chemically correct mixture. When we do, power, engine temperature, and exhaust gas temperature all begin to fall again. We couldn't see this before, with air-cooling, because the power we were making was overwhelming the engines the engine's cooling ability. But it makes perfect sense because heat release in combustion depends upon finding enough oxygen so that each and every hydrogen and carbon in the fuel is completely reacted to form water and carbon dioxide. Any fuel left over is potential chemical energy unreleased which is why running lean makes less power. On lay well cooled engine that is not detonating, you can jet down until it starts to slow down.

    Now back to detonation. The above explanation is the common one, but it leaves important questions unanswered. For example, why does detonating combustion travel at the local speed of sound, and not at normal burning speed? Why does the endgas auto ignite, rather than simply wait there like a stand of trees in the path of a forest fire? Understanding how this comes about helps to understand how the variables that affect detonation generate their effects and it helps to fend off the phenomenon that sets the upper limits on performance.

    There are two basic forms of combustion, deflagration and detonation. In deflagration, the propagation of combustion is carried out by simple convection; the hot combustion gas heats what is ahead of it, raising its temperature to the ignition point. Because this process of heating what lies ahead takes time, it is relatively slow. The burning of a quiescent gasoline air vapor is in fact slow only a foot or so per second. Combustion in an engine cylinder is much faster than this because of turbulence, which so wrinkles the flame front that its area becomes hugely enlarged. This area, multiplied times the slow quiescent combustion speed, computes out to a very large volume combustion rate.

    Detonation is a different animal, and not all gaseous mixtures will support detonation. It is a form of combustion in which the unburned material is heated to ignition at least partly by shock compression, as the detonation wave moves a the local speed of sound through the medium. This has to happen very quickly, so fuels with simple molecules or those with low stability lend themselves to this form of combustion. Now how does the endgas ignite by itself? It does so when its temperature is raised by any combination of effects to some critical value in the range of 900-1000 degrees F.

    In a running engine, air is drawn in at some ambient temperature, and this air then begins to pick up heat from the hot internal engine surfaces it contacts. Finally it enters the actual cylinder, where is it heated by even hotter surfaces. Trapped there, it is heated again by the process of compression.

    In this heating process, some little discussed chemical reactions begin to occur in the fuel. Called preflame reactions, these take the form of slow, partial breakdown of the least durable types of fuel molecule. Fuel hydrocarbons have three basic forms; straight carbon chains, branched chains, and ring structures. Temperature is a measure of average molecular activity, but there are always some gas molecules moving significantly faster than the others. These faster moving molecules hit and break some of the less durable fuel molecules, dislodging some of their more weakly bonded hydrogen atoms. This released hydrogen is very reactive (normally hydrogenous travel in bonded pairs, but his is atomic hydrogen) and instantly pairs with an oxygen from the air to form what is called a radical, a chemical fragment that is highly reactive because if contains and unpaired electron. Its attraction for the missing electron is so great that it can snap one out of other chemical species it happens to collide with, thereby breaking it down as well.

    At some point in the compression stroke, the spark ignites the mixture and combustion begins. The burned gases, being very hot, expand against the still unburned charge, compressing it outward into the squish band. This compression rapidly heats the unburned charge even more, accelerating the preflame reactions in it. As a rule of thumb, the rate of chemical reaction doubles every seventeen degrees F. All this while, the population of reactive molecular fragments radicals is increasing in the unburned endgas. If this process of heating takes long enough, and reaches a temperature high enough, this population of radicals becomes great enough that its own reaction rate one radical creating more and more through further reactions accelerates into outright combustion. This is autoignition.

    Now why does this heated, chemically changed endgas detonate instead of simply burning? The fuel in the endgas is no longer ordinary gasoline. The preflame reaction that have taken place in it have changed it into a violent explosive much like a mixture of hydrogen and air, or acetylene and oxygen. It is in a hair-trigger state, being filled with reactive fragments from preflame reactions. When it autoignites spontaneously, combustion accelerates almost instantly because the material is so easily ignited now. The combustion front accelerates to the local speed of sound, igniting the material it passes through simply by suddenly raising its temperature, through the shock wave it has now become.

    STOPPING THE SHOW

    Anything that contributes to lowering the temperature that the endgas reaches will make detonation less likely. Anything that slows the process of conversion from normal gasoline into a sensitive explosive, will make detonation less likely. Anything that speeds up combustion, so that is it completed before the conditions needed for detonation can develop fully, will make deto less likely.

    Therefore the following will work;

    (1) Lower intake temperature

    (2) Lower throttle position, lower volumetric efficiency, or reduced turbo boost the less mixture that enters the cylinder, the less it is heated by compression.

    (3) Lower intake pipe, crankcase, and/or cylinder, piston, or head temperatures. This year's Yamaha 250cc road race engine, for instance, has a copper cylinder head insert to conduct combustion heat away faster, resulting in a lower combustion chamber surface temperature.

    (4) Lower compression ratio. The less you squeeze it, the less it is heated.

    (5) A more breakdown resistant fuel, such as toluene or isooctane. If straight chain molecules are not present, the fuel will not be broken down so rapidly by preflame reactions.

    (6) A negative catalyst something that will either pin down active radicals or convert them into something harmless. Tetraethyl lead, MMT, or other antiknock compounds are the medicine.

    (7) Retarded timing shortens the time during which proknock reactions can take place.

    (8) Incylinder turbulence or anything else that will speed up combustion (faster burning fuel such as benzene). This works by completing combustion before the time bomb of preflame reactions cooks long enough to cause autoignition.

    (9) Higher engine rpm This simply shortens the time during which the mixture is held at high temp. In Honda experiments in the 1960's, they found that an engine's octane requirements began to decrease steadily over 12,000 rpm, and were under 60 octane up near 20,000. In a more accessible example, note that engines knock when they are "lugged" run at low rpm, wide open throttle and stop knocking promptly when you shift down a gear and let the engine rev up more. This stops deto by not allowing enough time for the reactions that cause it.

    (10) Redesigning troublesome exhaust pipes. Some pipes give great numbers on the dyno, but can't be used because they cause seizures. They either simply overcharge the engine in some narrow rpm band (pushing it into detonation just as too much turbo boost would do), or back pump mixture from the header pipe that has picked up too much heat (this is why nobody heat wraps header pipes anymore).

    (11) Avoiding excessive backpressure. Exhaust pipes always create back pressure, but the more there is, the higher the fraction of hot exhaust gas that will be unable to leave the cylinder during exhaust. Its heat, added to the fresh charge that next enters the cylinder, may push the engine over the line into detonation. Sometimes a one or two millimeter reduction in tailpipe ID will get you a couple of extra horsepower, but it may also push enough extra heat into the charge to make the engine detonate after a few seconds.

    The number of ways of playing footsie with detonation is endless, but nothing works every time. This guarantees that we will never be bored, and will never run out of seized pistons
    Plus an interesting related spiel on Fuels
    Studies have shown that if the fuel is divided, simply, into light, medium and heavy components, by the time the mixture reaches the combustion chamber, 70% of the light ends have evaporated, and only 30% of the heavier components have evaporated (thanks to Kevin Cameron who found that study last Sunday). Then, if that mixture of vaporized fuel in the combustion chamber is between 10/1 and 17/1, clean burning can begin, creating heat, and the eventual vaporization and burning of most of the rest of the fuel. And probably those “tail ends” help cool the piston, as they are the last to evaporate when all of the oxygen has been consumed in 13/1 mixtures. If you’ve seen the Youtube videos of combustion taking place in an engine, you can see that it’s not an explosion—it’s more like a controlled bonfire—ignition of mostly front end vapors takes place while droplets of heavier ends are still flying about, then the droplets seem to disappear as they finally become vaporized and burn as the piston continues to move through TDC and downward, and if tuning and fuel is optimal the highest pressure should occur at about 18 degrees ATC.
    Below is something I glued together also from Cameron but a lot less wordy and it has pics.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Cameron Detonation Cameron Pre ignition.jpg 
Views:	99 
Size:	642.6 KB 
ID:	311869  

  3. #17628
    Join Date
    5th April 2013 - 13:09
    Bike
    zuma50
    Location
    illinois
    Posts
    314
    I've often wondered if a piston machined in such a way that only a slight edge of the periphery of the crown was made to have a slight interference fit with the bore. It would act like a molded in ring... and with careful break in conform and wear to cylinder shape. It would still use a conventional ring underneath.

  4. #17629
    Join Date
    20th April 2011 - 08:45
    Bike
    none
    Location
    Raalte, Netherlands
    Posts
    2,822
    Quote Originally Posted by husaberg View Post
    DETONATION:...
    I won't quote husa's complete text here; I'd just like to say that I could not find anything wrong with it .

  5. #17630
    Join Date
    20th January 2010 - 14:41
    Bike
    husaberg
    Location
    The Wild Wild West
    Posts
    9,934
    Quote Originally Posted by Frits Overmars View Post
    I won't quote husa's complete text here; I'd just like to say that I could not find anything wrong with it .
    Other than it has a lot of Four stroke stuff.
    In some other more Four stroke related stuff he wrote the EX temp actually goes down when deto is occurring.

    I found something interesting that was written a few years ago about forged pistons heat vs Cast
    I know cast technology would have improved a lot since but I do wonder if some of the generalisations still hold true.
    I will scan it and add it soon.

  6. #17631
    Join Date
    22nd November 2013 - 16:32
    Bike
    STRIKE trike & KTM300 EXC TPI
    Location
    Perth, Western Australia
    Posts
    636
    Good stuff Husa. You must be in the lead for the most productive Googler for the year so far.
    “The only reason for time is so that everything doesn’t happen at once”

  7. #17632
    Join Date
    20th January 2010 - 14:41
    Bike
    husaberg
    Location
    The Wild Wild West
    Posts
    9,934
    Quote Originally Posted by ken seeber View Post
    Good stuff Husa. You must be in the lead for the most productive Googler for the year so far.
    As long as I get to keep my least productive bucket engine builder and KB soft porn King titles.

    The bit that interested me was on Page four to do with crown and ring land temps.
    As always keep clicking on them to get them easier to read.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	piston 1.jpg 
Views:	101 
Size:	581.2 KB 
ID:	311877   Click image for larger version. 

Name:	piston 2.jpg 
Views:	95 
Size:	691.9 KB 
ID:	311878   Click image for larger version. 

Name:	piston 3.jpg 
Views:	84 
Size:	752.0 KB 
ID:	311879   Click image for larger version. 

Name:	piston 4.jpg 
Views:	85 
Size:	774.0 KB 
ID:	311880   Click image for larger version. 

Name:	piston 5.jpg 
Views:	76 
Size:	698.3 KB 
ID:	311881  

  8. #17633
    Join Date
    13th September 2014 - 05:14
    Bike
    '76 RD-400C
    Location
    The Emerald City
    Posts
    240
    Could be I didn't see it, but the comments I've seen here on the ring groove gas-ports (whether drilled down vertically from the piston crown to hit the back of the ring groove, or horizontally above the ring as in Wobbly's photo) miss what I understood as the original idea . . . which was that in the event that the ring got to "floating" up to the top of the groove and thereby pinching off the gas pressure in back of the ring, leading to blow-by, these ports would always offer a continuous path for the gas pressure to the back of the ring. For what that's worth, LOL.

    Frits' description of the ring-groove findings at Aprilia certainly blows big holes in what I thought I "knew" about prudent practice as related to ring groove dims and placement. But that's why I'm here!!

    One thing does seem (emphasize that word) clear: Wobbly's suggestion that the area of the water jacketing of the head that lies directly over the squishband should be cooled as effectively as possible would seem to address several problems here. You want to minimize the "crevice volume" of trapped A/F mixture above the ring by various means, including placing the ring as high as possible, and reducing groove dims to a minimum per Frits/Thiel (scary to me!), for a power gain. Cooler squish area, so cooler and thus mechanically-stronger piston edge, should allow high placement of the ring without piston failure there, right?? And a cool squish area (and piston edge) ought to tend to quell detonation of whatever "crevice" gases remain. This idea of Wobbly's just seems to me like the deal sheneille for water-cooled two-strokes, a win-win, and easy to accomplish if you make your own two-piece cylinder head and water-jacket cover.

    Wobbly, when your piston-builder does those tiny half-moon gas-ports, they make them before turning the groove, right? And do they drill them or use an end-mill that small? IF it's an end mill, I wonder if they could rotate the piston slowly, without breaking that itty-bitty endmill in this high-silicon aluminum, to make slots instead of just half-holes, which might address your finding that the holes become less effective at high rpms when there is less charging time . . . ???

  9. #17634
    Join Date
    8th February 2007 - 20:42
    Bike
    TZ400
    Location
    tAURANGA
    Posts
    3,097
    The super cooled squishband concept has now proven itself beyond doubt in one application that needs it the most
    My KZ2 race engines with a straight line analogue ignition, that has way to much advance at peak and beyond, are now deto free.
    Under normal circumstances the squish gap would have to be held way big up at 1.3mm or the piston would begin to be eaten away
    over the boost port side with no provocation at all.
    Now I am down at 0.8mm with no divergent taper and its a mm wider as well - this would have spelled instant deto death previously due to the trapped end gases
    being overheated by the failing boundary layer conditions between the piston and head.
    Next step is the radiused piston with matching cool head squishband area, and yes I am hoping the two ideas will be synergistic ( better word for the day than ameliorated ).

    I havnt asked Wossner about the machining process, but I would imagine that the 1/2 moons are machined after the groove is done, as trying to keep the
    groove surface finish high when bouncing thru radial drilled holes would be nigh on impossible.

    The Celler Dweller is probably one of the most insightful engine technology commentators we have, and anyone would be hard pressed to find anything he has written that could be deemed suspect.
    Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.

  10. #17635
    Join Date
    20th January 2010 - 14:41
    Bike
    husaberg
    Location
    The Wild Wild West
    Posts
    9,934
    Quote Originally Posted by wobbly View Post

    I havnt asked Wossner about the machining process, but I would imagine that the 1/2 moons are machined after the groove is done, as trying to keep the
    groove surface finish high when bouncing thru radial drilled holes would be nigh on impossible.
    I wonder what order are the Pegs done then, they often overlap too.
    Where's Ken. Get him out of Bed.
    This is a kit the V8 crowd use.
    One of the DIY threads mentioned using a SS Hose clip as a drilling guide
    http://www.goodson.com/Repl.-Drill-Bit-.040-5-Pkg/
    Click image for larger version. 

Name:	GPT-BITS.jpg 
Views:	35 
Size:	8.0 KB 
ID:	311883Click image for larger version. 

Name:	gasportingtoolkits_10104188.jpg 
Views:	61 
Size:	108.1 KB 
ID:	311884

    Quote Originally Posted by marsheng View Post
    Thanks for the posts. For some reason I don't get emails when others post!! Need to look into that.

    The suggestion is exactly what I needed. Sounds like it's worth a try.

    Cheers Wallace
    Its on your setting one minute please caller.
    Click image for larger version. 

Name:	Email notifications.jpg 
Views:	46 
Size:	254.5 KB 
ID:	311887

    Added a few Maico Pics as well
    Disk Valve.
    Click image for larger version. 

Name:	normal_1974_Maico_MD250_Schnittmotor_HDB___.jpg 
Views:	66 
Size:	141.5 KB 
ID:	311896Click image for larger version. 

Name:	normal_1974_Maico_MD250_Schnittmotor_HDB__.jpg 
Views:	59 
Size:	152.8 KB 
ID:	311897


    Quote Originally Posted by wobbly View Post

    The Celler Dweller is probably one of the most insightful engine technology commentators we have, and anyone would be hard pressed to find anything he has written that could be deemed suspect.
    Sounds like a holiday Challenge but all to easy the answer, tis the pipe opening reeds but he was adamant he got that from Macolloch guy (brooks?)

  11. #17636
    Join Date
    13th April 2009 - 22:30
    Bike
    Maico Bimota 250
    Location
    Christchurch
    Posts
    269

    Maico Posting

    Thanks for the posts. For some reason I don't get emails when others post!! Need to look into that.

    The suggestion is exactly what I needed. Sounds like it's worth a try.

    Cheers Wallace
    ........Rules are for fools and a guide for the wise ..............

    http://www.marshland.co.nz

  12. #17637
    Join Date
    2nd March 2013 - 15:04
    Bike
    CBX125F NS50F NS90F NS-1
    Location
    Lower Hutt
    Posts
    330
    Quote Originally Posted by wobbly View Post
    The Celler Dweller is probably one of the most insightful engine technology commentators we have, and anyone would be hard pressed to find anything he has written that could be deemed suspect.
    I agree. Kevin Cameron wrote the following letter to someone named Muir in Australia a long long time ago.
    I was given a copy in 1976 or 77, so nearly 40 years. You might be surprised at how insightful he was that long ago.
    Apologies for the quality. Copiers were pretty crap in those days. Well worth a read though.
    Click image for larger version. 

Name:	Cameron, K Letter 1.pdf 
Views:	140 
Size:	1.09 MB 
ID:	311898

  13. #17638
    Join Date
    2nd March 2013 - 15:04
    Bike
    CBX125F NS50F NS90F NS-1
    Location
    Lower Hutt
    Posts
    330
    In another letter from Kevin Cameron to Mr Muir about 1975, he draws a diagram of how to create what we now call Boyesen ports, from the reed block to the transfers.
    Interesting that Boyesen patented this idea in 1975. I wonder who thought of it first?

  14. #17639
    Join Date
    12th May 2011 - 23:52
    Bike
    razor scooter(pink)
    Location
    Australia
    Posts
    370
    I asked Murray Sayle he's bound to know

  15. #17640
    Join Date
    13th June 2010 - 17:47
    Bike
    Exercycle
    Location
    Out in the cold
    Posts
    4,962
    Quote Originally Posted by lodgernz View Post
    In another letter from Kevin Cameron to Mr Muir about 1975, he draws a diagram of how to create what we now call Boyesen ports, from the reed block to the transfers.
    Interesting that Boyesen patented this idea in 1975. I wonder who thought of it first?
    Given that the US karters were adding reed blocks and additional carbs over the transfers very early on, probably one of them who didn't want to do the welding...

Thread Information

Users Browsing this Thread

There are currently 8 users browsing this thread. (1 members and 7 guests)

  1. jamathi

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •