DERVs and torque

[scarr89]

Why is it that DERVs produce so much torque in comparison to BHP?

I'v only just noticed that the standard PD150 has the same torque rating as a stock R32? But the R32 has almost 100bhp more and a massive engine?

How?!

[danny_p]

dervs don't rev

power is RPM multipluyed by torques, hence petrol engin ewith same torques makes a load more power as it revs

[xxChrisxx]

Why is it that DERVs produce so much torque in comparison to BHP?

I'v only just noticed that the standard PD150 has the same torque rating as a stock R32? But the R32 has almost 100bhp more and a massive engine?

How?!

Power (kW) = Torque (Nm) * RPM / 9.5488

Say both produce 300 Nm torque. The diesel at 2500 RPM and the petrol at 4500 RPM.
The associated power outputs are:
Diesel = 78 kW
Petrol = 141 kW

Peak torque output is not at the same RPM as peak power though.
Also the engine doesn't produce this figure across the entire rev range.

[scarr89]

Why is it that DERVs produce so much torque in comparison to BHP?

I'v only just noticed that the standard PD150 has the same torque rating as a stock R32? But the R32 has almost 100bhp more and a massive engine?

How?!

Power (kW) = Torque (Nm) * RPM / 9.5488


Say both produce 300 Nm torque. The diesel at 2500 RPM and the petrol at 4500 RPM.
The associated power outputs are:
Diesel = 78 kW
Petrol = 141 kW

Peak torque output is not at the same RPM as peak power though.
Also the engine doesn't produce this figure across the entire rev range.

Thanks alot mate, very 'simply' put 

Do petrols hold their torque for long in the rev range than DERVs?

[DOA]

Basically due to the fact that diesels use compression ignition (ie, squeeze it till it goes bang) they are more efficient at lower engine speeds and are incapable of revving very high due to the limited time that the fuel has to ignite and the incredibly high ignition pressures that must be withstood by the engine (the fuel pressure alone in modern diesels is incredible and would likely chop your hand of if you were daft enough to remove and injector and try spraying the fuel over yourself!). I think I am right in saying that Diesel fuel contains more energy than petrol, therefore they are capable of producing a higher torque at lower engine speeds from a given quantity of fuel and air. As pointed out however, power is related to torque and engine speed (the 9.5488 in the calculation presented by Chrisxx btw is a conversion factor for engine speed in radians per second so that you can use RPM in the calculation) so it is very difficult for a diesel engine to produce very high power outputs in comparison to a petrol engine capable of rotating at very high engine speeds.

[scarr89]

Basically due to the fact that diesels use compression ignition (ie, squeeze it till it goes bang) they are more efficient at lower engine speeds and are incapable of revving very high due to the limited time that the fuel has to ignite and the incredibly high ignition pressures that must be withstood by the engine (the fuel pressure alone in modern diesels is incredible and would likely chop your hand of if you were daft enough to remove and injector and try spraying the fuel over yourself!). I think I am right in saying that Diesel fuel contains more energy than petrol, therefore they are capable of producing a higher torque at lower engine speeds from a given quantity of fuel and air. As pointed out however, power is related to torque and engine speed (the 9.5488 in the calculation presented by Chrisxx btw is a conversion factor for engine speed in radians per second so that you can use RPM in the calculation) so it is very difficult for a diesel engine to produce very high power outputs in comparison to a petrol engine capable of rotating at very high engine speeds.

It all becomes clear as mud 

I gotcha. So diesels don't rev as much as the compressions makes the fuel ignite rather than a spark plug which is 'electronically controlled' right?

Are there diesels engines that use spark plugs instead of compression?

[rob.043]

Are there diesels engines that use spark plugs instead of compression?

No, thats just for petrol.

Bear in mind you are comparing turbo charged diesel engines to n/a petrol engines. Turbo a similarly sized petrol engine and it will provide big torque too, but more power as it revs.

[scarr89]

Are there diesels engines that use spark plugs instead of compression?

No, thats just for petrol.

Bear in mind you are comparing turbo charged diesel engines to n/a petrol engines. Turbo a similarly sized petrol engine and it will provide big torque too, but more power as it revs.

You mean the R32 right I get ya, what will a R32Turbo kick out and what about the 1.8Ts? How much torque they pushing out?

[dom]

Are there diesels engines that use spark plugs instead of compression?

No, thats just for petrol.

Bear in mind you are comparing turbo charged diesel engines to n/a petrol engines. Turbo a similarly sized petrol engine and it will provide big torque too, but more power as it revs.

You mean the R32 right I get ya, what will a R32Turbo kick out and what about the 1.8Ts? How much torque they pushing out?

My 1.8t is putting out around 245lb/ft.

[AudiA8Quattro]

Diesel engines also have a longer stroke, so more torque..