Performance tuning pdf

There are so many times the query needs to restructure,. There are so many parameters which will impact the performance of PostgreSQL. The PostgreSQL database admin has to check the load and tune the parameters according to the load. Following are few parameters we require to check for performance tuning of PostgreSQL. You can set it to high value. Setting this too low decreases crash recovery time, as more data is written to disk, but it hurts performance too since every checkpoint ends up consuming valuable system resources.

These are some most important parameters which we require to check at the time of PostgreSQL performance tuning activity. I hope this article will be useful to you. If you like this article or if you have any issues with the same kindly comment in comments section. Your email address will not be published. Skip to content. Of course the Suzuki case reed system was originally designed for motocross and later enduro bikes. It is in these 66 applications where this type of induction is in its element.

It highlights, once again, the importance of the transfer ports. With conventional reed engines the back transfer port, or boost port, can be made very large and, as it enters right into the inlet port and is free of obstruction, it flows well.

Case reed engines have two tiny boost ports and, because the transfer passagrs which feed these ports enter at such a strange angle, directional control of the transfer streams is not good.

Naturally, the entrance of the reed cage must be perfectly matched to the inlet manifold to ensure minimal air flow disruption. If the reed fixing screws protrude into the air stream, grind them off flush with the reed cage.

However, if the screws are well below the surface, fill the holes with Devcon F. Be sure to put a drop of Loctite blue grade on the fixing screws each time that they are refitted. Within the reed cage you will often find little steps and ridges which can be filed out.

When you do this, be sure to leave a 1mm wide seat for the reed to seal against and, when you refit the reed petals, carefully line them up with the cage openings. Unfortunately, some manufacturers make the petal fixing holes so much larger than the diameter of the fixing screws that the petals can be fitted seating over an area 2mm wide on one side and barely covering the cage opening on the other side. If you are not after a huge increase in high speed air flow, then I would recommend that you retain the standard reed cage and fit phenolic reed petals or, better still, a set of dual Boyesen petals.

Phenolic petals wear out fairly quickly, which is why most bike manufacturers prefer stainless steel petals. However, phenolic petals respond to the air requirement of the engine more quickly and they do not flutter and rebound off the cage to the same extent as stainless steel petals.

To increase the life of phenolic petals they should be carefully sanded around the edges, using grit wet and dry carborundum paper, before being fitted. Some petals are smooth on one side only, so be sure to fit these with the smooth side sealing against the reed cage.

When a large increase in high rpm air flow is required, a larger reed valve assembly will be necessary. There are special assemblies available for some engines but often it will be necessary to adapt a reed valve from a larger, or more potent, engine. This can be quite frustrating, as you won't find many dealers with reed valves in their parts bins for you to inspect for size.

The best way is to go to a motorcycle wrecker, cylinder in hand, and look through his range of reed valves. Don't look for a reed valve which will drop straight into the inlet tract of your cylinder, as it probably won't be much bigger than the standard assembly. Instead, look for a valve which is a little wider and perhaps a little higher than standard.

The fixing holes probably will not line up with the holes in your cylinder, but that is not a great problem providing the wrecker has the inlet manifold which matches the reed valve. Check that the inlet manifold has a hole of the correct size to suit your carburettor; if it does, you are in business. The next problem is enlarging the inlet cavity to suit the bigger reed cage. To accomplish this, you will have to use your judgement. Start by measuring the reed assembly and comparing its size with the reed cavity in the inlet port.

If it's 4mm wider, then grind 2mm off each side of the cavity and so on. When the reed valve fits the cavity, you can then decide what has to be done to fix the reed valve and manifold to the cylinder. If the fixing holes are close, then it may be possible to elongate the holes in the reed cage and manifold to align with the cylinder. In some cases, it will be a matter of filling the stud holes in the cylinder and then drilling and tapping new fixing holes.

In this instance, an aluminium plate with fixing holes to suit the TZ reeds is welded to the RD cylinder face. Before some special replacement reed assemblies are fitted, they have to be 68 modified in ways different to that outlined on preceding pages. This reed flows very well but it falls short in two areas, which could easily catch the unsuspecting tuner out. The first problem is that the screw heads on the lower side of the reed prevent the cage from seating properly against the base of the cylinder.

Thus an air leak can develop and spoil engine performance. What must be done is file the edges of the screw heads flush with the cage mounting face, so that the cage can seal against the cylinder base. The other problem involves the reed stop for the main i.

The stop is too flexible and actually rebounds the reed petal when it comes against the stop. This sends the petal into flutter and reduces high speed power. You will note that the Suzuki stop is much thicker, so longer fixing screws are required. If these are unobtainable, the holes in the stop can be countersunk to give the screws more bite. Before we close the subject of reed valve induction, there are a couple of don'ts which you should keep in mind. Don't ever bend the reed stops to increase reed lift and don't ever fit a spacer under the stop to increase reed lift.

Either practice will cause petal flutter at higher rpm, because the reed becomes unstable i. On the average motocrosser, increasing reed lift by just 0. The other don't is this: don't waste your time cutting the back out of the piston or enlarging the skirt windows. This weakens the piston and there is little or no gain in hp anywhere in the power range. The only exceptions to this rule would be in the case of desert racers, or bikes which are very pipey, if they don't have any holes high up on the piston skirt.

Drilling a pair of round holes just below the ring land will help cool the piston crown and little end, or if the bike is very peaky and nothing else has tamed the push of power, maybe a pair of holes will help. The holes shouldn't be too large: 10 to 13mm is plenty big enough for a or , and larger engines could use holes about 14 to 16mm in diameter.

After the holes are drilled, carefully chamfer them on the inside and outside of the piston, then dress the holes with grit wet and dry. These precautions will help prevent premature cracking of the piston skirt. Originally, the exhaust pipe was designed to get burnt gases out of the engine as quickly as possible. Then, as designers learned more about pressure waves, they attempted to make use of them to scavenge the cylinder of exhaust gases.

The basic theory of pressure waves is quite easy to understand, but the practical application of pressure wave phenomenon is very difficult to formulate. This is not to imply that the first exhaust you fabricate will be perfect. The Japanese manufacturers, and in particular Yamaha and Suzuki, know as much as anyone about exhaust tuning, but you will find they are constantly updating the expansion chambers on both their works and production racers, proving they are still looking for the best design.

Understanding exhaust design begins with an appreciation of the behaviour of sonic waves travelling through a pipe. These waves travel at a speed determined by the temperature and pressure of the outflowing exhaust gas. This speed always equals the speed of sound, which averages around ft.

Sonic waves have the strange property of being reflected back along the pipe they are travelling through, regardless of whether the pipe has an open or closed end. Even more peculiar is another fundamental law of acoustics which causes a pressure wave to invert its sign on reaching the open end of a pipe. A positive pressure wave, on reaching the pipe's open end, goes back up the pipe as a negative wave, and vice versa. Reflection from a pipe's closed end does not change sign, a positive wave stays positive.

The earliest exhausts were a piece of straight pipe, but these were not able to take 70 full advantage of putse waves to 'suck' exhaust gases out of the cylinder. On reaching the end of the pipe it was reflected as a negative wave, but with reduced intensity because much of its wave energy was lost to the surrounding atmosphere. However, some energy did rerriain and if, when the negative wave reached the exhaust port, the port was still open, it would assist in a small way in evacuating the cylinder.

This being the case, the wave would turn round and travel back down the exhaust still negative, then, on reaching the open end of the pipe, be reflected up again as a positive pressure wave. In theory it sounds good, but in practice the straight pipe exhaust never worked too well, primarily because so much kinetic energy was lost each time the sonic wave reached the open end of the exhaust pipe.

A megaphone, more correctly called a diffuser, is in effect a relatively efficient energy inverter. In a diffuser the walls diverge causing the sonic wave to react just as though it had reached the open end of the exhaust.

However, the reflected wave retains most of its energy and can create a vacuum as low as 6 psi. Obviously a pulse wave of this magnitude can be very effective in drawing exhaust gas out of the cylinder, and in pulling the fresh charge from the crankcase up through the transfer ports.

The exhaust port will close before the reflected positive wave arrives, to force the mixture back into the cylinder. This type of exhaust is referred to as an expansion chamber. When the positive wave reaches the diffuser, part of the wave is inverted and reflected as a negative wave to evacuate the cylinder. However, part of this wave continues on to be reflected by the reverse cone. Because of the pressure buildup caused by the small bleed hole, the reverse cone acts like a closed pipe, reflecting the wave with the same positive sign.

This strong positive pulse arrives just before the exhaust port closes, forcing any escaped mixture back into the cylinder, increasing power output and reducing fuel consumption.

On paper that theory, too, sounds very simple, but there is much more involved when we actually set about designing a system! Obviously the expansion chamber must be of the correct length to ensure the pulse waves are reflected to arrive at the exhaust port at the proper time. OOOrpm, the tuned length would be: The length of mm is measured from the piston face to the assumed reflection point of the reverse cone.

This point is half way along the cone but, because the top is cut from the cone, the point must be calculated mathematically. The first part of the expansion chamber, the header pipe, may be either a straight pipe with parallel walls, or a tapered pipe with diverging walls.

A tapered header pipe is to be preferred, as it will improve the power and power range; however, it is much more difficult to fabricate than the straight pipe. The actual length required for the header pipe can only be determined accurately by testing. Over the years, I have devised and tried all kinds of formulae to calculate the length of the header, but I've never found one that works too well.

It has been my experience that it is much quicker to make an educated guess and work from there. However, if you were to use a single stage diffuser, the header would be a little longer at to mm. Usually, you will find the shorter length in both instances to be very close to what is required for best performance.

It is important to note that the above rule for calculating the header length can work only if the exhaust port is of a standard diameter for that particular size of engine. Single stage refers to a single stage diffuser. The Exhaust Fig. Yamaha MX36O pipe. Also, keep in mind that the calculated length of the header is the measurement from the piston to the end of the header pipe. Therefore, when you fabricate the pipe, remember to subtract the length of the exhaust port.

In the first instance it increases chamber volume, which effectively broadens the power range. Secondly, its diverging walls reduce flow resistance both in and out of the cylinder. The burnt gases flow out easily with a minimum of turbulence and any fuel mixture which has spilled into the exhaust is rammed back into the engine more efficiently.

Thirdly, and this is the most important reason for the justification of tapered headers, the shallow taper allows the exhaust gas to expand and cool more gently. This results in less loss of kinetic pulse energy than if the gases were to expand rapidly and abruptly on passing from a straight header into the diffuser section of the expansion chamber.

The taper of the header is normally between 1. However, some manufacturers have used tapers as shallow as 0. If the diffuser taper is very shallow i. Conversely, if the exhaust port and flange is very long i. The total length of the header will be 40 x 6. The taper of the pipe will be 1. The next stage of the expansion chamber, the diffuser, is, as we mentioned earlier, a wave inverter. The duration and intensity of the inverted return wave is determined by the diffuser taper.

A shallow taper returns a wave of long duration and low intensity. Maximum power will be increased but at the expense of narrowing the power band. The length of the diffuser is determined by the diameter to which it expands, which should normally be 2.

If you have room on the bike, and you wish to experiment, you may be able to spread the power range by making the diffuser taper to 2. This move will at times suppress maximum power, but the improvement lower down the scale usually compensates. On many bikes, it is difficult to find room for a large diameter exhaust, so you may have to be satisfied with a less than perfect chamber. Most bikes have trouble catering for an exhaust in excess of mm diameter, so this could restrict the diffuser outlet to something closer to 2.

Generally, a two or three section diffuser is utilised, although some tuners. Road race engines and motocross engines with near road race porting require a three stage diffuser, due to the need for steeper angles of taper to pick up peak power. For example, a twin cylinder road race would use a diffuser with the first section tapering at 4.

If, after building an expansion chamber with a diffuser like this, you find that the engine is too peaky, then increase the length of the first stage of the diffuser. This will broaden the power band. Conversely, if the engine lacks peak power, decrease the length of the first diffuser section and lengthen the second stage. The parallel belly section of the expansion chamber naturally has the same diameter as the diffuser outlet, but we cannot calculate its length until we have arrived at a suitable size for the rear baffle cone.

A flat plate could do the same job but the wave duration would be so short that this would only occur over a very narrow rpm range. A cone, on the other hand, extends the duration of the pressure pulse, although reducing its intensity. This serves to broaden the engine's useful power band. This broadens the engine's effective Dower range and means that the bike's speed down the main straight will be less iffected by changing wind conditions during a race.

TABLE 4. These ingles have proved to give a good power range without suppressing maximum hp excessively. In our example, we will assume that an By halving this figure, mm, we can determine the mean reflection point of the baffle and then go back and calculate how long the belly section has to be to give us the tuned length of mm which we originally worked out. Unfortunately the results have not been as promising as expected. However, small gains have been made by some tuners working with 62cc and cc size cylinders.

If you wish to do some experimentation along these lines, start out using a baffle which has the first stage tapering at 4. The last section of the expansion chamber, called the 'stinger', is in reality a bleed pipe. Its function is to restrict gas flow out of the exhaust and create back pressure by slowly bleeding off exhaust gas. You may find that a minor reduction in pipe diameter will raise the power output, but do be careful.

A stinger pipe smaller in diameter or longer than specified could easily result in engine overheating and seizure. Therefore, I would suggest you make only small changes and then thoroughly test the pipe before going any smaller.

Engine overheating, in its early stages, is indicated by the presence of oil burnt dark brown under the piston crown. On the next stage the burnt oil turns black, until finally 'death ash' appears. After this, the piston can be holed at any time. Do not start with the smallest diameter and greatest length.

Most road race expansion chambers will require a stinger not more than mm long and of the smallest diameter indicated for each engine size. The Exhaust In the example we have been using right the way through, we would select a stinger 23mm in diameter id and about mm long. The addition of the stinger shortens the baffle cone; its final length can be calculated using the same formula as for the diffuser cone: To draw out the shape of either the diffuser or baffle cone on a piece of sheet metal is quite difficult.

The cone's dimensions, when rolled out flat, can be worked out geometrically, or the sizes can be calculated mathematically. I prefer the latter method. Assuming we were going to fabricate the baffle cone for this expansion chamber, we would calculate its size, before being rolled into a cone, in this way.

The next dimension we must calculate is the length of the cone when measured along the tapered wall, dimension AC. The result, 1. The final check which we should make involves quite a simple calculation. We multiply the baffle cone or diffuser taper by nx 2. In this example the baffle taper is If all of our calculations have been correct, this figure should be very similar to the angle 0, which we calculated to be Now that all these calculations have been made, we have the dimensions and angles necessary to drawn the cone onto the piece of sheet metal from which the cone is to be cut.

Actually, I recommend that you first make a template on a piece of stiff cardboard, and then transfer the shape to the sheet metal, as it is much easier to draw accurately on cardboard than on steel.

Then adjust a pair of compasses to draw an arc, the radius of which will be equal to dimension AC, in this case mm. Using the cross as the centre, scribe the arc. Draw a line from the centre through this point and you have the outline of the template.

Once you have a template you can go ahead and cut out the metal required for the baffle cone. Note a similar series of calculations are required to get the diffuser cone, or tapered header pipe shape, drawn onto a template. If you have not had any experience with sheet metal, then I would suggest that you take your templates to a sheet metal fabrication shop and get them to cut and roll the cones. Actually, it is a little more difficult than that. Building a system for a motocross or enduro bike must be one of the worst forms of torture yet devised by man.

The main point to keep in mind, when you set about making the pipe fit, is to keep the header pipe entry into the diffuser cone smooth FIGURE 4. If the header entry is not smooth, gas flow out of the cylinder will suffer because any abrupt change in direction here, where gas velocity is very high, creates turbulence.

Remember that an expansion chamber's basic function is to maintain and preserve the wave energy at a high level, so you will not want to do anything to cause a loss of this energy which is used to evacuate and recharge the cylinder. Sonic waves are willing to follow even the most tortuous curves without any reduction in pulse energy. Therefore, you can cut and resection the cones and parallel belly section to make the chamber fit your bike.

The 86 pulse waves will not know whether the system is straight, or bent all over the place. The Exhaust Correct. There are two ways to cut and resection an expansion chamber to form a bend: the easy way and the right way. When you cut a cone and reweld it the easy way, you will lose out in two ways.

The correct method to form a bend is to make the first cut right through the cone and then take the second cut only as far as the cone's centre. When the cone is resectioned, the piece which is cut out is welded into the outside of the bend. This technique keeps the length of the cone, through the centre, the same as it was when straight. The next thing you must think seriously about is an effective muffler. I'm not too happy having to fit mufflers to a road racer, but this is what nearly all sanctioning bodies require.

A muffler just adds more weight and knocks the edge off maximum power, also this requirement is just another example of discrimination against motorcycles. Racing cars are not required to be fitted with mufflers and yet bikes, running on the same road circuits and speedways, must be silenced. On the other hand, I feel every effort should be made to silence motorcycles to a whisper when they are being used on public roads, on private and government land, deserts and reserves etc.

The noise of two wheelers in these areas is upsetting a lot of people and driving wildlife back into more remote areas. If you want your freedom to ride in the places where you are currently permitted to ride, then you are going to have to make sure that the people who live around those areas are free of the noise of your motorcycle.

There are several choices open as to the type of silencer which can be fitted. Tuned length is not altered. Tuned length is shorter by this amount ' Fig. Normally the Super Trapp is supplied with eight discs fitted, plus four spares which may be added if you want a little more power at the expense of more noise. If you wish, you can make your own detachable muffler. To reduce weight and increase the silencing efficiency, consider fabricating a muffler from aluminium instead of steel tube.

Steel tends to resonate more readily than aluminium and this reduces the effectiveness of a steel silencer. Riders operating very close to housing estates should seriously endeavour to reduce noise to the minimum by making their muffler double walled. Sliding another piece of tube over the muffler reduces resonance from the inner wall, hence less noise is emitted from the body of the muffler. Mufflers for road race bikes and karts are best fabricated as part of the expansion chamber.

As the allowable noise level is reasonably high, usually around 96 dbA, this type of silencer does not have to be so elaborate. Preferably, the main body of the silencer should be 16 gauge aluminium. It is not of much use if your exhaust has a good quiet muffler, but the expansion chamber is cracked and almost falling off because of incorrect mounting. You will note in both instances, where the exhaust is attached to the machine by welded brackets, the large area over which the load is supported.

This reduces the possibility of the chamber or the bracket cracking. If the mount does start to crack, a length of 6mm rod can be welded into the corners where the mount angles away abruptly from the chamber. A saddle is fabricated out of fairly heavy steel, usually 4mm thick by 13mm wide, to support the chamber, which is held in place by two springs.

Usually, the header pipe is secured to the exhaust flange by either a system of springs or a large flange nut. Whatever method is used, make sure the header pipe will not slip out of the flange in the middle of a race. This means if a flange nut is the method of attachment, it must be tight and properly prevented from loosening by the attachment of two springs from the header pipe to the nut as is done on the older Bultacos.

The thing to watch here is that the header and flange should overlap by at least 25mm. This reduces exhaust leakage and makes it much harder for the header pipe to jump out of the flange. The simpler joint is used by the majority of motorcycle manufacturers for economic reasons. As you can see, if the exhaust port is made the correct diameter, the header pipe is too large, or if the manufacturer makes the header pipe the correct size, the exhaust port ends up too small.

Steel flange. Perforated tube 8mm. I Glasswool. Many people don't worry too much about exhaust flange leakage, yet every effort should be made to prevent this, as any leakage reduces the pressure in the chamber, upsetting sonic wave speed and changing the tuned length of the system. If the leak is serious enough, the chamber will cease to evacuate the cylinder properly. Instead, the suction pulse wave draws air into the chamber through the leaky joint. Then the pressure wave will push this air up the exhaust port, and into the cylinder.

Every off reader, sooner or later, stalls or bogs in a creek, and when this occurs you don't want water to seep into the motor to worsen the situation in which you find yourself. All exhaust flanges leak to some degree, but slip joint flanges appear to be the worst, until carbon begins to build up and seal the joint. Unfortunately, racing engines have the barrels and chambers removed too frequently for the carbon to seal properly, so it is necessary to use some sort of exhaust putty to stop leakage.

I use Silastic RTV silicone to seal all exhaust joints. The carbon and gum deposits upset gas flow by constricting the internal dimensions of the header pipe and by creating turbulence in the system.

These effects adversely alter performance, therefore the system must be regularly cleaned out. This may be done by heating the outside of the system to a red heat and occasionally directing the flame down the header pipe to ignite any oil gum present.

If the chamber is made of 16 or 18 gauge steel, it is an idea to tap the chamber quite vigorously with a piece of broom handle as this will help free the carbon clinging to the walls. Wait until the chamber cools a little before you do any banging, otherwise the walls could easily be deformed.

Chambers made of 20 or 22 gauge material are much more difficult to clean, as the heating will often cause the chamber walls to deform slightly, and banging with a stick while the chamber is still hot, to loosen baked on carbon, is definitely out. About all you can do is not use an intense flame, but wait until the chamber is quite cool before attempting to free the burned carbon ash.

You can tap the chamber lightly with a rod or you can throw a few rough stones or a short length of chain inside and give it a good shake. The oil in the chamber gives off foul fumes, which will soon have your eyes watering and your throat hurting, so be warned. The other part of exhaust maintenance involves a careful inspection for any sign of cracks.

These usually appear in the mounting bracket proper, or around where the brackets are welded to the main body of the chamber. Chambers constructed of very light gauge material will often crack along seams in the parallel belly section, as this 92 section tends to pulse in harmony with the system's sonic waves. Chapter 5 Carburation THE BASIC requirement for any carburettor is that it meters the fuel and air in such proportions as to be easily combustible and hence enable the engine to produce good power over a wide rpm band.

Usually, the mixture we want is around or , i. If the carburettor is not able to do this, flat spots and engine surging will result, spoiling performance. For this reason we have to be very selective as to the type and size of carburettor we choose for our particular engine. To understand more fully what we should be looking for in a carburettor to suit our engine's requirements, we need to go back to basics and get to know how a carburettor works. The inlet system consists of the fuel bowl, float and needle valve or needle and seat.

The fuel, before passing to the metering systems, is stored in the fuel bowl, and it is maintained at the correct level by the float and needle valve.

A high fuel level will richen the mixture, earning excessive fuel consumption and poor running. On the other hand, a low fuel level can be even more serious due to the leaning effect it has. This may result in flat spots when accelerating out of turns, or, in extreme cases, the engine could overheat and seize. A high fuel level may be due to an incorrectly adjusted float, or a needle and seat which is not seating properly and shutting off the fuel when the float rises to the correct level.

A low fuel level condition may also be the result of an improperly adjusted float, but it could be due to the fuel lines or the needle and seat being too small to flow sufficient fuel to keep the fuel bowl full.

The fuel bowl is always vented so that the fuel is being mixed according to the outside air pressure. Without a vent, accurate metering would not be possible, as fuel vapours would build up pressure in the bowl and displace fuel out through the main and idle metering circuits.

The float is usually made of brass stampings soldered together into an airtight assembly, but it may also be formed from plastic or a closed cellular material. Brass floats are resistant to all types of fuel except nitromethane, and generally plastic or cellular floats are not damaged by most common fuels.

However, if you intend to use a fuel other than petrol or methanol, it is wise to check with the carburettor manufacturer regarding possible float damage. The needle and seat is usually made of steel, although some needles may have a Viton coating on the tip. The Viton promotes excellent sealing and acts as a shock damper, but it should not be used with fuels containing any alcohol or nitro.

The needle valve controls the flow of fuel into the bowl, so some thought must be given to increasing its flow capabilities if an alcohol fuel is being used. Generally, it is not possible to obtain larger needle and seat assemblies for this purpose, so it will be necessary to modify the seat by very carefully drilling the fuel discharge holes oversize.

I would recommend you use a pin vice to hold the drill when you do this. The idle system provides a rich mixture at idle and low speeds when not enough air is being drawn through the carburettor to cause the main system to operate. When the throttle slide is nearly closed, the restriction to air flow causes a high vacuum on the engine side of the throttle slide. This high vacuum provides the pressure differential necessary for the idle system to operate.

The normal air pressure Conversely, turning the screw clockwise richens the mixture by reducing the amount of air passing through the air bleed circuit. Bypass hole. Air Weed holes. Pilot or idle jet. Instead, the pilot hole acts as a supplementary air bleed to further atomise the fuel after it passes through the idle jet. Then as the throttle opens wider the pilot hole, too, begins to spray fuel. This serves to supply the engine with additional fuel until the air speed through the carburettor increases sufficiently to start the main system flowing fuel into the air stream.

As the throttle is opened wider and engine speed rises, so the air speed through the carburettor increases, bringing the main fuel delivery system into operation FIGURE 5. If a carburettor of the correct size has been selected, this should happen at about quarter throttle as the idle circuit reaches the limit of its fuel flow capability at that time.

A serious flat spot would result if the main system was not operational and supplying the additional fuel required to prevent a lean mixture. Because atmospheric pressure is higher than the pressure in the crankcase, air rushes in through the carburettor to equalise the pressure. On its way into the crankcase, the air has to speed up as it passes through the carburettor bore. This speeding up of the air reduces the pressure below atmospheric inside the carburettor bore, allowing normal atmospheric pressure Pressure drop or vacuum within the carburettor varies with the engine speed and throttle opening.

Wide open throttle and peak rpm give the highest air flow, and consequently the highest pressure difference between the fuel bowl and the needle jet's discharge orifice. This, in turn, produces the highest rate of fuel flow into the engine. To compensate for various engine displacements and engine operational speeds, a range of carburettors with a variety of bore diameters are available to create the pressure drop necessary to bring the main fuel circuit into operation.

A small carburettor will provide a higher pressure difference, at any given rpm and throttle opening, than a larger carburettor, assuming engine size is the same. This is a very important aspect of carburation, which partly explains why the biggest is seldom the best.

If the signal being applied is too weak due to the bore diameter being excessively large , this could delay fuel discharge in the main system, causing a flat spot due to excessive mixture leanness. Also, fuel atomisation will not be good at any engine speed.

Poor atomisation spells poor combustion and reduced horsepower, so, if you must err when selecting a carburettor, err on the small side, as the effect on performance will be far less devastating. In the main fuel system, metering is controlled by the main jet, the needle jet and the needle. The main jet controls fuel flow from the fuel bowl into the needle jet.

An increase in the main jet diameter richens the mixture, but there are other aspects worthy. The shape of the jet entry and exit, as well as thqjfore finish, also affect fuel flow. Carburettor manufacturers measure the flow of every jet, and then number the jet according to its flow characteristics, not according, to the nominal bore diameter.

For this reason, jets used to meter petrol should not be drilled to increase their size if you desire accurate fuel metering. An engine burning alcohol does not require such accurate metering, unless fuel consumption is a consideration, so jet drilling may be in order when large jets are not available. In the case of Mikuni carburettors in particular, there is another problem.

Due to its popularity, outsiders are manufacturing main jets to suit these carburettors but, unfortunately, many of the jets fall far below the level of quality and flow parity of the genuine Mikuni item. I have seen many jets improperly drilled. Some had deep spiral grooves in the bore, others had steps and tapers in the bore.

To assist in atomisation and high speed fuel flow metering, many carburettors also 96 incorporate an air bleed circuit in the main metering system. Needle jet. Air bleed holes. Main jet. When the fuel is thus broken down into smaller particles, combustion speeds up because there is more fuel surface area exposed to the combustion flame. The air bleed also acts as a compensator or air corrector in adjusting high speed fuel flow requirements.

The reason for this is that the pressure drop in the carburettor is in direct proportion to the air speed through its bore and, in turn, fuel flow is in direct proportion to the pressure drop thus created. However, the actual mass of air passing into the engine does not remain in proportion with air speed, so the mixture strength would become excessively rich with increases in air speed through the carburettor if uncorrected.

Fuel flow, in both the jdle and main circuits, is also influenced by the throttle slide cutaway size at throttle openings between one eighth and half throttle FIGURE 5. Increasing the cutaway size reduces airflow resistance and leans the mixture. This occurs because air flow into the engine is greater due to reduced air flow resistance but fuel flow does not increase proportionately, as the larger cutaway reduces the pressure drop within the carburettor bore. The Mikuni Powerjet carburettor is still rather new to road racing motorcycles although Yamaha have been using them since , being originally designed for snowmobile racing engines.

T Fig. The delivery tube hangs in the air intake, in front of the throttle slide, and is connected through a metering orifice to the float bowl. Up to almost full throttle, the Powerjet carb operates just like any other Mikuni but, as full throttle is approached, the air moving past the tip of the Powerjet delivery tube creates a depression great enough to allow atmospheric pressure to push fuel through the power metering jet and up the delivery tube into the airstream.

The Powerjet therefore has the effect of enriching the mixture at full, and close to full throttle, and then only when air velocity is high enough to create a vacuum of sufficient intensity to discharge fuel. It is, in effect, a load sensitive enrichment system which allows for more accurate i. Fast and efficient statements take up fewer hardware resources and perform better.

In contrast, an unoptimized inefficient statement will take longer to complete and take up more computing power. Inefficient use of computing power means that the database will take longer to respond to user requests.

In practice, that means that whenever a user interacts with the interface the response time will be higher as the database tries to find the necessary information. Network administrators and developers regularly use performance tuning to improve database performance and maintain a premium user experience.

There are many reasons why a SQL server may be running slow. Factors from slow queries to performance bottlenecks, virtualized resource contention, and hardware limitations all contribute to poor performance. However, finding the root cause of a slow server is complex because of the large list of potential culprits. Most of the time, poor performance is related to badly written queries and indexing making inefficient use of resources rather than hardware limitations.

A database monitor will enable you to look deeper into the cause of poor performance and deliver a better end-user experience for your customers. Database monitoring tools are essential for managing SQL performance because they allow you to pinpoint the root cause of inefficiency. Monitoring tools like SolarWinds Database Performance Analyzer are ideal for identifying common issues like SQL bottlenecks and highlighting the cause of the problem.

What makes bottlenecks tricky is that there are various ways that they can be manifested. There are four types of bottlenecks that can affect the performance of a server: memory , disk , CPU , and the network itself. Managing bottlenecks becomes even more difficult if you have multiple bottlenecks active at the same time.

SolarWinds Database Performance Analyzer helps you to identify the root cause of active bottlenecks. For general performance tuning, you also have a variety of guidance to help you tune statements. By having this information on hand you can start to make tangible changes to your performance tuning strategy and improve the experience of your end-users.

As discussed above, query run time is an important consideration when trying to maintain SQL performance, the longer a query runs the more resources the hardware has to use to process the request.

Reducing the query run time will allow you to get more mileage out of your hardware, and support better database performance. There are three main factors that increase the query run time: table size , joins , and aggregations.

If a query needs to interact with a table that has too many rows then the software will need to work harder to process that query. Likewise, if your query joins multiple tables together this is going to affect performance. Similarly queries that use aggregations to generate a result also require more resources. It is important to note that the runtime of a query can also be increased if lots of other users are running queries at the same time.