The mode of operation of the engine is one of the main factors affecting the wear rate of its parts. It's good when the car is equipped automatic transmission or a variator that independently chooses the moment of transition to a higher or lower gear. On machines with “mechanics”, the driver is engaged in switching, who “spins” the motor according to his own understanding and not always correctly. Therefore, motorists without experience should study at what speed it is better to drive in order to maximize the life of the power unit.
Low speed driving with early shifting
Often, driving school instructors and old drivers recommend that beginners drive “in tightness” - switch to top gear upon reaching 1500–2000 rpm crankshaft. The first give advice for safety reasons, the second - out of habit, because before the cars had low-speed engines. Now this mode is only suitable for a diesel engine, whose maximum torque is in a wider rev range than a gasoline engine.
Not all cars are equipped with tachometers, so inexperienced drivers with this style of driving should be guided by speed. The early shift mode looks like this: 1st gear - moving from a standstill, shifting to II - 10 km / h, to III - 30 km / h, IV - 40 km / h, V - 50 km / h.
Such a shifting algorithm is a sign of a very relaxed driving style, which gives an undoubted advantage in safety. The downside is an increase in the wear rate of parts of the power unit, and here's why:
- The oil pump reaches its nominal capacity from 2500 rpm. Loading at 1500–1800 rpm causes oil starvation, especially suffer connecting rod bearings sliding (liners) and compression piston rings.
- Burning conditions air-fuel mixture far from favorable. In the chambers, on the valve plates and piston bottoms, carbon deposits are heavily deposited. During operation, this soot is heated and ignites the fuel without a spark at the spark plug (detonation effect).
- If you need to rev the engine sharply when driving downhill, you press the accelerator, but acceleration remains sluggish until the engine reaches its torque. But as soon as this happens, you shift into a higher gear and the crankshaft speed drops again. The load is large, there is not enough lubrication, the pump poorly pumps antifreeze, hence overheating occurs.
- Contrary to popular belief, there is no fuel economy in this mode. When you press the gas pedal fuel mixture is enriched, but not completely burned, which means it is wasted.
Owners of vehicles equipped with on-board computer, it is easy to be convinced of the uneconomical movement "in tightness". It is enough to turn on the display of the instantaneous fuel consumption.
Such a driving style wears out the power unit intensively when the car is operated in difficult conditions- on ground and country roads, fully loaded or trailer. Do not relax and car owners with powerful motors with a volume of 3 liters or more, capable of accelerating sharply from the bottom. After all, for intensive lubrication of rubbing engine parts, you need to keep at least 2000 rpm of the crankshaft.
Why is high crankshaft speed harmful?
The driving style “sneaker on the floor” implies constant crankshaft spinning up to 5–8 thousand revolutions per minute and late gear shifting, when engine noise literally rings in the ears. What is fraught with this driving style, in addition to creating emergencies on road:
- all components and assemblies of the car, and not just the engine, are tested maximum loads during the service life, which reduces the total resource by 15–20%;
- due to the intense heating of the engine, the slightest failure of the cooling system leads to a major overhaul due to overheating;
- exhaust pipes burn out much faster, and with them an expensive catalyst;
- transmission elements wear out rapidly;
- since the crankshaft speed exceeds the normal speed by almost twice, the fuel consumption also increases by 2 times.
The operation of the car "at break" has an additional negative effect associated with the quality pavement. Movement on high speed on rough roads literally kills the suspension elements, and in the shortest possible time. It is enough to fly the wheel into a deep pothole - and the front strut will bend or crack.
How to ride?
If you are not a race car driver and not an adherent of tight driving, who finds it difficult to retrain and change driving style, then to save the power unit and the car as a whole, try to keep the engine operating speed in the range of 2000-4500 rpm. What bonuses will you receive:
- Mileage up to overhaul the motor will increase (full resource depends on the brand of car and engine power).
- Thanks to the combustion of the air-fuel mixture in the optimal mode, you can save fuel.
- Fast acceleration is available at any time, you just need to press the accelerator pedal. If there is not enough speed, immediately switch to a lower gear. Repeat the same steps when moving uphill.
- The cooling system will function in operating mode and protect the power unit from overheating.
- Accordingly, suspension and transmission elements will last longer.
Recommendation. On most modern cars equipped with high speed gasoline engines, it is better to shift gears when the threshold of 3000 ± 200 rpm is reached. This also applies to the transition from higher to lower speed.
As stated above, dashboards cars don't always have tachometers. For drivers with little driving experience, this is a problem, since the crankshaft speed is unknown, and the beginner does not know how to navigate by sound. There are 2 options for resolving the issue: buy and install on a dashboard electronic tachometer or use the table, which shows the optimal engine speed in relation to the speed in different gears.
| Position of the 5-speed gearbox | 1 | 2 | 3 | 4 | 5 |
| Optimum crankshaft speed, rpm | 3200–4000 | 3500–4000 | at least 3000 | > 2700 | > 2500 |
| Approximate vehicle speed, km/h | 0–20 | 20–40 | 40–70 | 70–90 | over 90 |
Note. Considering that various brands and modifications of machines, there is a different correspondence between the speed of movement and the number of revolutions, the table shows the average indicators.
A few words about coasting from a mountain or after acceleration. In any fuel supply system, a forced idle mode is provided, which is activated under certain conditions: the car is coasting, one of the gears is engaged, and the crankshaft speed does not fall below 1700 rpm. When the mode is activated, the supply of gasoline to the cylinders is blocked. So you can safely brake the engine at top speed without fear of wasting fuel.
The choice of the required camshaft should begin with two important decisions:
First, let's check how we determine the operating rpm range, and how the choice of camshaft is determined by this choice. Maximum engine speeds are usually easy to isolate, as they directly affect reliability, particularly when the main parts of the block are conventional.
Maximum engine speed and reliability for most engines
| Maximum engine speed | Estimated working conditions | Expected service life with related parts |
| 4500/5000 | Normal movement | Over 160,000 km |
| 5500/6000 | "Soft" forcing | Over 160,000 km |
| 6000/6500 | Approximately 120,000-160,000 km | |
| 6200/7000 | Forcing for everyday driving/ "soft" racing | About 80,000 km |
| 6500/7500 | Very "hard" street riding or "soft" to "hard" racing | Less than 80,000 km in street driving |
| 7000/8000 | Only "hard" races | Approximately 50-100 runs |
Keep in mind that these recommendations are general. One engine can hold up much better than another in any category. How often the engine is accelerated to maximum speed is also very important. However, as general rule you need to be guided by the following: maximum speed engine must be below 6500 rpm if you are building a boosted engine for everyday driving and require it reliable performance. These engine speeds are normal for most part limits and can be obtained with medium force valve springs. So if reliability is the primary goal, then a top speed of 6000/6500 rpm would be a practical limit. Although the decision on the maximum RPM required may be relative simple process based in principle on reliability (and maybe cost), the inexperienced engine designer may find determining the engine's operating speed range a much more difficult and dangerous task. Valve lift, stroke duration and cam profile camshaft will determine the powerband, and some inexperienced mechanics may be tempted to choose the "biggest" possible camshafts in an attempt to increase maximum power engine. However, it is important to know that maximum power is only needed for a short time when the engine is at maximum speed. The power required from most uprated engines is far below the maximum power and RPM; in fact, a typical boosted engine can "see" a full opening throttle valve only a few minutes or seconds for a whole day of work. However, some inexperienced engine builders ignore this obvious fact and choose camshafts more by intuition than by guidance? If you suppress your desires and make a careful choice based on real facts and possibilities, then you can create an engine capable of delivering impressive power. Always keep in mind that the camshaft is pretty much a compromise part. After a certain point, all increases are given at the price of power for low revs, loss of throttle response, efficiency, etc. If your goal is to increase the number Horse power, then first make modifications that add maximum power by improving intake efficiency, as these changes have less of an effect on power at low rpm. For example, optimize the flow in the cylinder head and in the exhaust system, reduce the flow resistance in the intake manifold and in the carburetor, then install a camshaft in addition to all the above "set". If you use these techniques judiciously, the engine will produce the wider power curve possible for your investment of time and money.
In conclusion - if you have a car with automatic transmission, then you need to be conservative when choosing the valve timing of your camshaft. Too long valve opening will limit engine power and torque at low rpm, which are essential elements in ensuring good acceleration and starting the car from a standstill. If your car's torque converter stops at 1500 rpm (typical for many standard transmissions), then a camshaft that puts out good torque, though not necessarily maximum power, at 1500 rpm will provide good acceleration. You may be tempted to use a high stop torque converter and long valve timing in an attempt to achieve best result. However, if you are using one of these torque converters with normal traffic then their efficiency at low speeds will be very low. Fuel efficiency will suffer quite a lot. For an everyday car, there are more efficient ways to improve low rpm acceleration.
Let's summarize the main elements of choosing a camshaft. First, for everyday driving, the maximum engine speed must be maintained at a level not exceeding 6500 rpm. RPMs above this limit will noticeably shorten the life of the engine and increase the cost of parts. While a "normal" engine can benefit from as much valve lift as possible, too much valve lift will reduce engine reliability. For all high lift camshafts, bronze valve guides are a necessary item to ensure long term bushing service life, but for valve lifts of 14.0 mm or more, even bronze guide bushings cannot reduce wear to a level acceptable for normal applications.
The longer the valves are held open, especially inlet valve, the more maximum power the engine will produce. However, due to the variable nature of camshaft timing, if valve timing or valve overlap goes beyond a certain point, all the extra maximum power will come at the cost of low-end performance. Camshafts with intake strokes up to 2700 measured at zero valve lift are good replacements for standard camshafts. For high-powered engines, the upper limit of the duration of the intake stroke of more than 2950 is the property of a purely racing engine.
Valve overlap causes some torque loss at low rpm, however, these losses are reduced when valve overlap is carefully selected for the application - from about 400 for camshafts standard engines up to 750 or more for special applications.
Valve timing, valve overlap, valve timing and cam center angles are all related. It is not possible to adjust each of these characteristics independently on single cam engines.
Fortunately, most camshaft specialists have spent many years creating cam profiles for power and reliability, so they can offer a camshaft that suits your needs well. However, do not blindly accept what the masters offer you; you now have the information you need to competently discuss camshaft specifications with camshaft manufacturers.
After all, the camshaft is one of the parts of the intake system. It must match with the cylinder head, intake manifold and exhaust system. Volume intake manifold and the size of the exhaust manifold pipes must be matched to match the power curve of the engine. In addition to this, the air flow rate in the carburetor, the number of chambers, the type of activation of the secondary chamber, etc. also have a noticeable effect on power.
Almost every driver is well aware that the resource of the engine and other components of the car directly depends on the individual driving style. For this reason, many car owners, especially beginners, often think about what speed is best to drive. Next, we will consider what engine speeds you need to keep, taking into account different road conditions during vehicle operation.
Read in this article
Engine life and revs while driving
Let's begin with competent operation and constant maintenance optimal speed engine allows you to increase engine life. In other words, there are operating modes when the motor wears out the least. As already mentioned, the service life depends on the driving style, that is, the driver himself can conditionally "regulate" given parameter. Note that this topic is the subject of discussions and disputes. More specifically, drivers are divided into three main groups:
- the former include those who operate the engine at low speeds, constantly moving "pulled".
- the second should include such drivers who only periodically spin up their motor to above-average speeds;
- the third group is considered to be car owners who constantly maintain the power unit in a mode above medium and high engine speeds, often driving the tachometer needle into the red zone.
Let's understand in more detail. Let's start with driving on the "bottom". This mode means that the driver does not raise the speed above 2.5 thousand rpm. on gasoline engines and holds about 1100-1200 rpm. on diesel. This style of driving has been imposed on many since the days of driving school. Instructors authoritatively state that it is necessary to drive at the lowest speeds, since in this mode biggest savings fuel, the engine is least loaded, etc.
Note that in driving courses it is advised not to turn the unit, since one of the main tasks is maximum safety. It is quite logical that low speed in this case is inextricably linked with driving at low speeds. There is logic in this, since slow and measured movement allows you to quickly learn how to drive without jerks when shifting gears on cars with manual transmission, teaches a novice driver to move in a calm and smooth mode, provides more confident control over the car, etc.
Obviously, after receiving driving license this driving style is further actively practiced on own car turning into a habit. Drivers of this type they begin to get nervous when the sound of a hyped motor begins to be heard in the cabin. It seems to them that the increase in noise means a significant increase in the load on the internal combustion engine.
As for the engine itself and its resource, too “sparing” operation does not add to its service life. Moreover, everything happens exactly the opposite. Imagine a situation when a car is moving at a speed of 60 km / h in 4th gear on even asphalt, the speed is, say, about 2 thousand. In this mode, the engine is almost inaudible even at budget cars fuel consumption is minimal. At the same time, there are two main disadvantages in such a ride:
- it is almost completely impossible to accelerate sharply without switching to downshift, especially on "".
- after changes in the road surface, for example, on slopes, the driver does not downshift. Instead of shifting, he simply presses harder on the gas pedal.
In the first case, the motor is often outside the “shelf”, which does not allow you to quickly disperse the car if necessary. As a result, this driving style affects general security movement. The second point directly affects the engine. First of all, driving at low revs under load with a strongly depressed gas pedal leads to detonation of the motor. The specified detonation literally breaks the power unit from the inside.
In terms of consumption, the savings are almost completely absent, since a stronger pressure on the gas pedal on overdrive under load causes enrichment fuel-air mixture. As a result, fuel consumption increases.
Also, “pull-in” driving increases engine wear even in the absence of detonation. The fact is that at low speeds, the loaded rubbing parts of the motor are not sufficiently lubricated. The reason is the dependence of the performance of the oil pump and the pressure it creates. engine oil in from all the same engine speeds. In other words, plain bearings are designed to operate under hydrodynamic lubrication conditions. This mode involves the supply of oil under pressure into the gaps between the liners and the shaft. This creates the desired oil film, which prevents wear of the mating elements. The effectiveness of hydrodynamic lubrication is directly dependent on engine speed, that is, more revs the higher the oil pressure. It turns out that with a heavy load on the engine, taking into account the low speed, there is a high risk of severe wear and breakage of the liners.
Another argument against driving at low speeds is a reinforced engine. In simple words, with a set of revolutions, the load on the internal combustion engine increases and the temperature in the cylinders rises significantly. As a result, part of the soot simply burns out, which does not happen when permanent operation on the "bottom".
High engine speed
Well, you say, the answer is obvious. The engine needs to be revved more strongly, as the car will respond confidently to the gas pedal, it will be easy to overtake, the engine will be cleaned, fuel consumption will not increase so much, etc. This is true, but only in part. The fact is that constant driving at high speeds also has its drawbacks.
High speeds can be considered those that exceed the approximate figure of about 70% of the total number available for a gasoline engine. With the situation is slightly different, since units of this type are initially less revving, but have a higher torque. It turns out that high revolutions for engines of this type can be considered those that are behind the “shelf” of diesel torque.
Now about the engine resource with this driving style. Strong spinning of the engine means that the load on all its parts and the lubrication system increases significantly. The temperature indicator also increases, additionally loading. As a result, engine wear increases and the risk of engine overheating increases.
It should also be borne in mind that at high speed modes, the requirements for the quality of engine oil increase. Lubricant should provide reliable protection, that is, meet the declared characteristics for viscosity, oil film stability, etc.
Ignoring this statement leads to the fact that the channels of the lubrication system when constant driving at high RPMs, they can clog up. This happens especially often when using cheap semi-synthetics or mineral oil. The fact is that many drivers change the oil not earlier, but strictly according to the regulations or even later than this period. As a result, the liners are destroyed, disrupting the operation of the crankshaft and other loaded elements.
What speed is considered optimal for the motor
To save engine life, it is best to drive at such speeds, which can conditionally be considered average and slightly above average. For example, if the “green” zone on the tachometer suggests 6 thousand rpm, then it is most rational to keep from 2.5 to 4.5 thousand rpm.
In the case of atmospheric internal combustion engines, designers try to fit the torque shelf in this range. Modern turbocharged units provide confident traction at lower engine speeds (the torque shelf is wider), but it is still better to spin the engine a little.
Experts claim that optimal modes work for most motors is an indicator from 30 to 70% of maximum number rpm while driving. Under such conditions power unit minimal damage is done.
Finally, we add that it is periodically desirable to spin up a well-heated and serviceable motor with quality oil by 80-90% when driving on flat road. In this mode, it will be enough to drive 10-15 km. Note that this action do not need to be repeated often.
Experienced motorists recommend spinning the engine almost to the maximum once every 4-5 thousand kilometers traveled. This is necessary for different reasons, for example, so that the cylinder walls wear out more evenly, since with constant driving only at medium speeds, a so-called step can form.
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In materials about cars, the expressions are often used " high revs"," large torque. As it turned out, these expressions (as well as the relationship between these parameters) are not clear to everyone. So let's talk about them in more detail.
Let's start with the fact that the engine internal combustion is a device in which the chemical energy of a fuel that burns in working area, is converted into mechanical work.
Schematically, it looks like this:
The combustion of fuel in the cylinder (6) causes the piston (7) to move, which in turn causes the crankshaft to rotate.
That is, the expansion and contraction cycles in the cylinders actuate crank mechanism, which in turn converts the reciprocating motion of the piston into rotational motion of the crankshaft:
What the engine consists of and how it works, see here:
So, the most important characteristics engine are its power, torque and speed at which this power and torque are achieved.
Engine speed
The commonly used term "engine revolutions" refers to the number of revolutions of the crankshaft per unit time (per minute).
Both power and torque are not constant values, they have a complex dependence on engine speed. This relationship for each engine is expressed by graphs similar to the following:
Engine manufacturers are struggling to ensure that the maximum torque of the engine develops in the widest possible range of revolutions (“the shelf of the torque was wider”), and the maximum power is achieved at speeds as close as possible to this shelf.
Engine power
The higher the power, the great speed develops auto
Power is the ratio of the work performed in a certain period of time to this period of time. In rotary motion, power is defined as the product of torque and angular velocity rotation.
Engine power has recently been increasingly indicated in kW, and previously it was traditionally indicated in horsepower.
As you can see in the graph above, maximum power and maximum torque are achieved at different crankshaft speeds. The maximum power for gasoline engines is usually achieved at 5-6 thousand revolutions per minute, for diesel engines - at 3-4 thousand revolutions per minute.
Power curve for diesel engine:
In practical terms, power affects speed characteristics auto: the higher the power, the more speed the car can develop.
Torque
Torque characterizes the ability to accelerate and overcome obstacles
Torque (moment of force) is the product of the force on the arm of the lever. In the case of a crank mechanism, this force is the force transmitted through the connecting rod, and the lever is the crank of the crankshaft. The unit of measure is Newton meter.
In other words, torque characterizes the force with which the crankshaft will rotate, and how successfully it will overcome rotational resistance.
In practice, the high torque of the engine will be especially noticeable during acceleration and when driving off-road: at speed, the car accelerates more easily, and off-road, the engine withstands loads and does not stall.
More examples
For a more practical understanding of the importance of torque, let's give a few examples on a hypothetical engine.
Even without taking into account the maximum power, some conclusions can be drawn from the graph reflecting the torque. We divide the number of revolutions of the crankshaft into three parts - these will be low revolutions, medium and high.
The graph on the left shows a variant of the engine that has high torque at low speeds (which is equivalent to high torque at low speeds) - with such an engine it is good to drive off-road - it will "pull" out of any quagmire. The graph on the right shows an engine that has high torque at medium speeds (medium speeds) - this engine is designed for use in the city - it allows you to accelerate quite quickly from traffic light to traffic light.
The following graph characterizes an engine that provides good acceleration even at high speeds - with such an engine it is comfortable on the track. Closes charts universal motor- with a wide shelf - such an engine will pull it out of the swamp, and in the city it allows you to accelerate well, and on the highway.
For example 4.7 liter Gas engine develops a maximum power of 288 hp. at 5400 rpm, and a maximum torque of 445 Nm at 3400 rpm. And the diesel 4.5-liter engine installed on the same car develops a maximum power of 286 hp. at 3600 rpm, and the maximum torque is 650 Nm at a "shelf" of 1600-2800 rpm.
The 1.6-liter X engine develops a maximum output of 117 hp. at 6100 rpm, and the maximum torque of 154 Nm is reached at 4000 rpm.
The 2.0-liter engine delivers a maximum output of 240 hp. at 8300 rpm, and a maximum torque of 208 Nm at 7500 rpm, being an example of "sportiness".
Outcome
So, as we have already seen, the relationship between power, torque and engine speed is quite complex. Summing up, we can say the following:
- torque responsible for the ability to accelerate and overcome obstacles,
- power responsible for top speed car,
- A engine speed everything complicates, since each value of revolutions corresponds to its own value of power and torque.
And in general, everything looks like this:
- high torque at low rpm gives the car traction for off-road driving (such a distribution of forces can boast diesel engines). At the same time, power can already become a secondary parameter - remember, for example, the T25 tractor with its 25 hp;
- high torque(or better - “torque shelf) at medium and high speeds makes it possible to accelerate sharply in city traffic or on the highway;
- high power engine provides high top speed;
- low torque(even when high power) will not allow to realize the potential of the engine: being able to accelerate to high speed, the car will take an incredibly long time to reach this speed.
