Many motorists often think about how to extend the life of their car and save on fuel without noticing that the key to this is in their right hand. Choosing the right crankshaft rotation range is a fundamental skill for any driver who wants to have his or her car in the right hand. combustion-engine There's no magic number on a tachometer that's suitable for all situations, but there are clear physical principles for the piston group.
Understanding the processes inside cylinders at different speeds avoids critical operating modes that lead to accelerated wear of parts. VAG turbocharged BMWThey have their own specifications, but the basic mechanics are the same for them. In this article, we will examine why driving "traction" can be more dangerous than high speeds, and determine the "gold range" for daily use.
Process physics: torque and power
To determine which speeds are best to operate a car, you need to clearly distinguish two key concepts: torque And torque is the thrust, the force that pushes the car forward, while power shows how long the engine can take that thrust as it increases speed, and peak torque is usually achieved at medium revs, which makes this range the most efficient for acceleration.
When operating at low revs, when the tachometer arrow barely rises above the 1000-1500 mark, the engine experiences severe loads. crankshaft It's subject to a lot of torsion, and the lubrication system may not be able to handle the oil supply to the remote high-pressure friction nodes, a phenomenon often referred to as "knocking" or "thumping fingers," and it's extremely destructive to the piston group.
⚠️ Warning: Long driving at revs below peak torque under load (in a slide or when accelerating) causes vibrations that destroy engine cushions and crankshaft bearings faster than driving at high speeds.
High revs, in turn, increase the wear rate of rubbing surfaces, but ensure better self-cleaning of the engine and more efficient operation of the lubrication system due to high oil pressure. However, constant operation in the red zone of the tachometer leads to overheating and thermal destruction of parts. The optimal mode for most civil engines is the range from 2500 to 3500 rpm with active acceleration.
Impact of revolutions on fuel consumption and ecology
There is a common belief that the lower the speed, the lower the fuel consumption, which is only partially true and only works in a steady, non-accelerated mode. When you try to accelerate or climb uphill at low speeds, the electronic control unit (ECU) has to enrich the fuel-air mixture so that the engine does not stall. fuel It can grow in a paradoxical way.
The most economical mode for the engine is the movement in the highest gear with the minimum possible, but stable pressure on the gas pedal. For modern atmospheric engines, this is often the range of 2000-2500 rpm Turbocharged units, thanks to the thrust on the "bottom", can economically go and 1500-1800 rpm, but only if the turbine does not enter the active boost mode constantly.
In addition, the engine is operating at too low speeds, negatively affects the environment: the catalytic converter and particulate filter work effectively only at a certain temperature of the exhaust gases. When driving at low speeds, the neutralization system does not warm up to operating temperature, which leads to the release of harmful substances and rapid coking. catalytic converter.
Why are diesels more economical at low speeds?
Diesel engines have a higher efficiency and a huge torque at low revs, which allows them to effectively pull the car without having to spin the crankshaft to high speeds, unlike gasoline counterparts.
Engine resource: myths about high speeds
Many drivers are afraid to spin the engine, believing that it will instantly kill the engine. In fact, periodic short-term speed increases of up to 4000-5000 rpm are useful for the engine. In this range, effective cylinder purging, burning of soot on spark plugs and valves, and also prevents the formation of deposits in the exhaust system.
The main enemy of the resource is not high speed of rotation, but sharp load changes and work in resonant zones. Constant driving in gas-to-floor mode on a cold engine is guaranteed to lead to bullying in the cylinders, since the thermal gaps have not yet reached the calculated values. Oil starvation cold start - the main cause of wear in the first minutes of work.
Modern materials and manufacturing technologies allow engines to be used Honda, Toyota and Mazda But a motor that is constantly in a gentle 1500 rpm mode may be even less powerful than a car that is periodically shaken at high speeds. It is important to let the engine run to the full range of its performance.
☑️ Checking before active driving
Working modes: city, highway and overtaking
In urban environments characterized by frequent stops and starts, it is difficult to stick to ideal turns. It is important to avoid creeping mode in first or second gear when the engine is unstable. Try to keep the revolutions above 2000 when driving in the flow to have a thrust reserve for maneuver.
On the track, the situation is different: long-term traffic at high speeds requires a transition to high gear. For 5-speed mechanics, the optimal range will be 2500-3000 rpm at a speed of 110 km / h. Six-speed boxes allow you to reduce this figure to 2000-2200 rpm, which favorably affects acoustic comfort and fuel consumption.
When overtaking, short-term speed up to or close to the cut-off is a normal operating mode, the engine is designed to give maximum power to this range, fear of pressing on the gas when overtaking can lead to an emergency, while a short-term mode of full load will not cause any harm to the heated engine.
| Mode of traffic | Optimal revolutions (atmospheric) | Optimal speeds (turbo) | Purpose of the regime |
|---|---|---|---|
| Warming up | 1000-1200 rpm | 1000-1200 rpm | Stabilization of gaps |
| City (calm) | 2000-2500 rpm | 1800-2200 rpm | Savings and traction |
| The track (cruiser) | 2500-3000 rpm | 2000-2500 rpm | Minimum wear and tear |
| Dynamic acceleration | 3,500-5500 rpm | 2500-4500 rpm | Maximum power |
Problems of low speed under load
And the particular thing that we need to focus on is what's called pull-out driving, which is when the driver is turning on high gear at low speed and trying to accelerate without going down, and at that point, the pistons are under tremendous pressure and the rods are working at a break. knock-off and damage the shaky piston group.
When driving at low revs under load, the lubrication system also suffers, the oil pressure in the system is directly dependent on the speed of rotation of the crankshaft. At low revs, the pressure may not be enough to create a stable oil film in friction pairs, especially in the camshaft bearings.
⚠️ Warning: If you hear metal ringing or vibration when you press the gas at low revs, switch to low gear immediately, and ignoring this signal will lead to major repairs.
In addition to mechanical damage, driving at low speeds contributes to the formation of soot. Unburned fuel settles on the valves, candles and the bottom of the piston. Over time, this soot can cause potassium ignition, when the engine continues to work after turning off the ignition due to red-hot particles of soot.
The rule of the thousand: Try not to dip below 1,000-1200 units on a running engine under load. This is the universal lower safety limit for most gasoline engines.
Specificity of modern engines and downsizing
The modern auto industry is moving towards reducing engine volume while maintaining or increasing power, and 1.0-litre or 1.2-litre turbocharged engines have become the norm. EcoBoost from Ford or TSI from VolkswagenThey have a narrow operating range and require more careful attitude to the choice of transmission.
Because of their low volume and high boost pressure, these engines tend to overheat and detonate when operating at low revs under high load. It is critical for them to switch down at any hint of lack of traction. Their maximum efficiency zone is often shifted to the 2000-3000 rpm range where the turbine goes to the boost.
Owners of CVVs should note that these transmissions often keep their speeds at one point during acceleration, which may create the illusion of the engine running at its limit, although it is actually in the zone of maximum efficiency. However, long driving on a track with fixed high speeds (above 4000) for variator pairs is undesirable due to the thermal load of the belt.
Modern small turbo engines require more frequent gear shifts and more careful control of the speed than the old atmospheric millionaires.
How to extend the life of the motor through speed control
For maximum extension of the engine life, it is recommended to maintain a balance. You should not constantly "gurl up" at low revs, but you also do not need to drive the engine to cut off every day. The golden mean is a confident movement in the range of 2500-3500 rpm if you need acceleration and 2000-2200 rpm with uniform movement.
Regularly, at least once a week or before a trip on the highway, it is useful to let the engine run at high speeds (4000-5000 rpm) for a short time, this will help burn out the deposits in the exhaust system and prevent coking rings. The main condition is that the engine must be fully heated to operating temperature.
Watch the cooling system and the oil quality. At high speeds, the lubricating properties of the oil increase many times over, and using poor-quality oil when driving actively can lead to liners turning or bullying in minutes.
Is it harmful for the engine to go for a long time at maximum speed?
Prolonged movement at speeds close to maximum power (red zone) creates extreme thermal and mechanical loads. Although the engine is able to withstand this mode, the resource of its parts (especially piston rings and valves) in this case is exhausted much faster, this is acceptable for short-term overtaking, but not for constant driving.
Is it true that diesel cannot be rotated?
Diesel engines have a smaller operating speed range and are generally not designed for long-term operation at high speeds (above 4000-4500 rpm). However, short-term increase in speed before cutoff is useful for regeneration of the particulate filter (DPF) and cleaning the exhaust system from the soot.
What is the best way to run a new engine?
During the break-in period (the first 1000-2000 km), it is recommended to avoid both very low and very high revs. The optimal range is 2000-3000 rpm with frequent changes in operation mode. You should not keep a constant speed for long, it is useful to vary the speeds so that the parts are rubbed in different modes.
Does the octane number of gasoline affect the permissible speed?
Yes, using gasoline with an octane number below the manufacturer's recommendation reduces the detonation resistance of the fuel. At high revs and loads, this can lead to detonation that destroys the pistons. High loads and high revs should be avoided on low-octane gasoline.