Is it less harmful to redline a diesel than a petrol?
Just an idea, but I know that petrols redline due to the fact you can only make bits of metal go so fast before things start to go wrong.
BUT I know the diesel combustion cycle takes longer...so to me, it seems that as diesels still use the same basic engine design (pistons, con rods etc), it seems that a diesel almost restricts itself. as the same sort of engine design (4 cylinder) can rev some 4000rpm higher when it's a petrol.
Obviously thrashing them from cold is still a no no.
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I think there are 2 primary reasons why diesels don't rev:
1. The diesel is injected almost at TDC, and there is therefore a very limited window in which to injet the fuel and get it to burn before the piston goes too far past TDC and you lose the power stroke. As the engine speeds up, this window gets shorter, but the rate of injection remains the same, so there comes a point where you simply can't inject the fuel fast enough - unless you use larger injectors, but this causes problems with slow running.
2. The diesel burns in liquid phase as soon as it is injected, so it does not absorb a load of energy from the pistons during the compression phase like petrol does - run a diesel too fast and the pistons tend to melt!
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RichardW
Is it illogical? It must be Citroen....
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I think there are 2 primary reasons why diesels don't rev:
The weight of the rotating components in Diesel engines tend to be heavier than petrol engines which presumably also restricts the ability to rev.
However why diesels don't rev wasn't the exam question! Harming the engine by taking it to the red line was the question posed.
I suspect that it does no more harm to red line than petrol. Given the power/torque charachteristics of a diesel there is little point in using maximum revs though.
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I didn't think you could harm it, because of the governor on a diesel which prevents it revving past a certain point. Certainly does on my 306 - quite hairy when you're trying to overtake something...
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Good thrashing usually does a diesel a lot of good. Provided everything is in good condition such as the cambelt etc.
I give my Megane dCi a good 'exercising' from time to time.
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Its as harmfull to a diesel as petrol if redlined when cold/hot Red line is a warning that the oil pump is on verge of not being able to supply engine with oil.as and when needed.Reason why engine ecu`s have a cutout so preventing any long period of redlining.as in diesel pumps/ecu`s
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Steve
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Key point as follows:
Typical turbo diesel;
Max torque @ 1800rpm / Max power at 3500 rpm / redline 4500 rpm.
Typical petrol;
Max torque @ 3500 rpm / Max power @ 6000 rpm / redline 6500 rpm.
Why red line the diesel?
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Key point as follows: Typical turbo diesel; Max torque @ 1800rpm / Max power at 3500 rpm / redline 4500 rpm. Typical petrol; Max torque @ 3500 rpm / Max power @ 6000 rpm / redline 6500 rpm. Why red line the diesel?
For the same reason you would a petrol, when you change up you need to be between peak torque and peak power to get best acceleration. So in your next gear you'd better make sure you're at more than 1800 rpm to complete that tight overtaking manoeuvre.
As said above, diesls work at higher pressures than petrols because of the higher compression ratios to make them go. This means the pistons, rods and crankshaft need to be stronger, therefore heavier. This leads to higher forces for the bearings, crank, rods and block to withstand.
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>> Key point as follows: >> >> Typical turbo diesel; >> Max torque @ 1800rpm / Max power at 3500 rpm / >> redline 4500 rpm. >> >> Typical petrol; >> Max torque @ 3500 rpm / Max power @ 6000 rpm >> / redline 6500 rpm. >> >> Why red line the diesel? >> For the same reason you would a petrol, when you change up you need to be between peak torque and peak power to get best acceleration. So in your next gear you'd better make sure you're at more than 1800 rpm to complete that tight overtaking manoeuvre.
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No reason to redline the diesel, as long as the diesels revs drop to above 1800 you will get strong acceleration in the next gear.
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Further point 1800rpm in 4th on my TDCi 130 Mondeo is approx 40mph, thus acclerating to 4000 (well short of the redline) will take me to nearly 90!
A similar petrol engined car would have to be in 2nd or 3rd pulling approx 12mph/1000 to be near it's max torque peak and would need to rev to nearly 8000rpm to reach 90 in the same gear!
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