Diesel engines never rev as high as petrol engines due to the fact that the piston has to travel further for its full rotation, while a petrol engine uses its shorter stroke to move the piston in quicker bursts, meaning the engine speed can be faster.
Diesel engines normally have lower redlines than comparably sized gasoline engines, largely because of fuel-atomization limitations; even a small diesel engine, such as a Yanmar 2GM20 found on a sailboat, has a redline of 3400 RPM continuous, with a maximum 1-hour rating of 3600 RPM.
Diesels cannot run at high RPMs due to low fuel burn rate, whereas gasoline engines can. Because the redline of diesel engines is lower, the parameters of the engine are typically optimized for running at these lower RPMs.
As a consequence of a higher compression ratio (longer stroke and turbocharger), diesel engines produce more torque which means you get more acceleration off the line.
Most diesel engines have the peak torque produced between 2000 – 2500 RPM. Maintaining your RPM at around 2000 RPM will give you the maximum efficiency and will also keep the engine rev happy. Try and quickly up shift to higher gears, so that you can maintain a lower RPM at high speeds.
Diesel engines, because of the weight and compression ratio, tend to have lower maximum RPM ranges than gasoline engines (see Question 381 for details). This makes diesel engines high torque rather than high horsepower, and that tends to make diesel cars slow in terms of acceleration.
Over-revving can cause damage to your valve train by causing a valve to stay open for too long – this leads to valve float. Valve float occurs when a valve is stuck in between open and closed. This will cause an immediate loss of power.
The maximum RPM of any engine is called its 'Redline'. Diesel automotive engines redline at around 4500 rpm. Where as petrol engine goes around 6500 to 7000 rpm.
The engine gets its maximum torque between 1600 and 2300 rpm and even when towing my 2.5 tonne caravan up hills, I have never needed to rev it higher than 3000 rpm. That's the thing about diesels. They can be slow revving and still make good power due to their high torque.
As mentioned earlier diesel fuel is denser and contains 39.6 MegaJoules/liter of energy compared to 33.7 MegaJoules/liter of gasoline. This indicates that every time the diesel fuel is burnt more amount of energy is transferred to the pistons thus increasing the torque on the crankshaft.
Smaller, usually high-performance, engines such as motorcycles and sports cars normally have higher redlines. Gasoline automobile engines typically will have a redline at around 5500 to 7000 rpm. Motorcycle engines can have even higher redlines because of their comparatively lower reciprocating mass.
Aston Martin Valkyrie - 11,100rpm
To build the engines, Aston sought help from Cosworth, and this has resulted in a naturally aspirated V12 engine with an insane 11,100rpm redline.
It's often recommended to redline a diesel engine sometimes, because this way you clean the carbon buildup and soot. Remember, redline a day keeps the mechanic away.
The only guaranteed way to unclog a clogged injector properly is by removing the injectors from the engine.
The lifespan of a diesel fuel injector
The life expectancy of a good quality diesel fuel injector is around 150,000 kilometres. They should be checked out by a professional at around this time.
The best way to clean fuel injectors on a regular basis is to use a diesel fuel cleaner additive. This can be added to the fuel tank periodically to cycle through your engine. If done regularly, maybe once or twice a month, it can keep gunk and debris from building up in your fuel injection system.
Cons of diesel cars
Diesel fuel usually costs more. Servicing can be more expensive, although you don't need to do it as often. Diesel cars produce a lot more NO2. Diesel engines can be slightly noisier.
Though diesel cars and trucks may cost more upfront, they're often worth it in the long run. Diesel is a richer source of usable energy than gasoline. According to the Department of Energy, diesel motors typically get as much as 35% more miles to the gallon.
Diesel is also better for longer journeys because of it's on-average increased fuel economy.
While your car's engine revs, at cruise, at around 2,000 rpm, a turbo's turbine can reach rotational speeds of more than 280,000 rpm.
No, in the short run, driving your vehicle at a high RPM does not hurt your engine. Occasionally, redlining the engine does not mean that it will break down – engines are designed to operate way beyond their specified redline limits. However, that doesn't mean you should redline your engine often.
Slow-Speed Engines means diesel engines having a rated speed of less than 400 rpm. Medium Speed Engines diesel engines having a rated speed of 400 rpm or more; but, approximately less than 1200 rpm. High-Speed Engines means diesel engines having a rated speed of approximately 1200 rpm or more.