Each car has its own unique engine sound. Even the same model with the same mileage sounds different. And the point is not even in the exhaust pipe and not in the loads, but in the unit itself. The main difference is engine speed. The thing is that each power unit has its own wear, which dictates its characteristics, both driving and idle.
The RPM of an engine can tell a lot about its condition. They should be observed both at idle and during medium and high loads, since this is the only way to determine how "he althy" the power unit is. If the engine cannot idle at all, there are several reasons for this: different compression in the cylinders, the carburetor adjustment is broken, or the ignition timing is incorrectly set. If, after checking and normalizing all these parameters, the work has not been restored, then it is worth thinking about internal problems, which, most likely, come down to wear on the piston rings or cylinders. In addition, it will be accompanied by increased smoke.
Highidle speed of the engine can also be dictated by incorrect adjustment of the carburetor, but for injection units such a malfunction is excluded, here a malfunction of the control unit is possible. If, nevertheless, the fuel system is carbureted, then the engine idle speed is set using the idle adjusting screw or two screws that control the amount of mixture supplied to the cylinders, as well as its composition. These screws are called "quantity" and "quality".
Besides this, there is also an ignition. Regardless of whether it is contact or not, the wrong ignition timing leads not only to increased wear of the crank mechanism, but also to increased noise due to high speeds. They can be reduced.
Engine speed can be reduced by shifting the ignition earlier or later. This is done with the engine warm and the carburetor properly adjusted. It is also worth remembering the high voltage in the ignition distributor. This is done by rotating its body in the direction of rotation of the slider - later, or if on the contrary, then earlier.
In addition, you should pay attention to the engine speed under shift loads. If the unit is able to touch the car at 1000-1200 rpm, then this indicates its "flexibility", since it is at this time that all the torque is used. If the maximum torque is shifted to the higher side of the revolutions - to 1500, then this already indicates some wear of the connecting rod and piston group.
If the average speed when driving is 2000-3000, but the speed is low, then this indicates the same. But in this case, the problem may not be in the unit itself. This may be the result of clutch slippage. There may already be many other problems and malfunctions, the elimination of which has its own specific character.
Thus, you should always remember that engine speed is an important indicator that you constantly need to monitor and immediately look for the reason for their change.