GolfGTIforum.co.uk
General => General discussion => Topic started by: scarr89 on 01 January 2012, 14:23
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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?!
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dervs don't rev
power is RPM multipluyed by torques, hence petrol engin ewith same torques makes a load more power as it revs
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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.
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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 :smiley:
Do petrols hold their torque for long in the rev range than DERVs?
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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.
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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 :smiley:
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?
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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.
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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?
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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.
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Diesel engines also have a longer stroke, so more torque..
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Thanks alot mate, very 'simply' put :smiley:
Do petrols hold their torque for long in the rev range than DERVs?
Petrol engines will tend to make their peak torque higher up the rev range.
Diesels tend to have peak torque across a wider % of the available revs.
Peak torque is sometimes described as 80+% of max torque. (it's the description i'm using here).
This is why DERV torque curves tend to look flat, and petrol torque curves tend to look like a hill.
This is obviously a bit of a sweeping statement, as you can get peaky diesels and petrols with flat torque curves.
When you start adding forced induction, you can get engines to do basically whatever you want.
Hope that answers your question without me being a car bore.
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I just been reading up some figures on my own car a 2001 gt-tdi 115bhp and it says mine produces 285 Nm 210 lb-ft Torque which surprised me does this sound right?Source of info here http://www.parkers.co.uk/cars/reviews/facts-and-figures/volkswagen/golf/hatchback-1997/21196/
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Yep, sounds right. Thats why Diesels have beefier gearboxes, driveshafts etc, to deal with the torque and very different gearing to deal with the lack of revs available from the engine. The easy way of checking would have been to use Chrisxx's formula using the torque peak revs, if the power is higher than the 115BHP then somethings not right. There is another very easy check you can make if you have the torque and power curves on the same scale but I doubt your diesel will rev high enough to see it.
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Yes 115bhp Tdi Pd has 210 ft lbs of torque, i have the same engine in my Sharan.
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Gota love a dirty DERV :grin:
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Gota love a dirty DERV :grin:
For sure :cool:
Great excuse to post a graph lol
(http://i7.photobucket.com/albums/y276/Rhyso/Audi%20A3/OY57UTM.gif)
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Should have posted this graph then :tongue:
(http://img28.imageshack.us/img28/1655/adami.gif)
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Should have posted this graph then :tongue:
(http://img28.imageshack.us/img28/1655/adami.gif)
Not my car though is it......if I'm going to brag, I'm going to brag about my own car :grin: :grin:
Give me a few months and mine might be pushing more than Adam's anyway :lipsrsealed: :evil:
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Over 400 torque. Fml. Is the red line the bhp right? Hw come it says 213 but is no where near it on the graph?
Bhp sells car...your torque would win races :smiley:
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Red line is the old power with just a remap I think.
Top blue one is BHP and lower blue is torque :undecided:
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Over 400 torque. Fml. Is the red line the bhp right? Hw come it says 213 but is no where near it on the graph?
Bhp sells car...your torque would win races :smiley:
You're reading it wrong
BHP is on the left axis and is the top lines are BHP
Torque is on the right axis and are the two lower lines
Red is PRE-DPF removal
Blue is POST DPF removal :afro:
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Over 400 torque. Fml. Is the red line the bhp right? Hw come it says 213 but is no where near it on the graph?
Bhp sells car...your torque would win races :smiley:
You're reading it wrong
BHP is on the left axis and is the top lines are BHP
Torque is on the right axis and are the two lower lines
Red is PRE-DPF removal
Blue is POST DPF removal :afro:
Gotcha :smiley:
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Lets not forget there is potently more to come from that :evil:
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Shoulda posted this one :tongue:
(http://i790.photobucket.com/albums/yy183/codling1234/DOM.gif)
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Dom that looks like an excessive amount of torque. :smiley:
The DERV have bigger drive shafts right for the increased torque right :huh:, So when the 1.8T guys get to lots of torque do you have to uprate the drive shafts? Have never heard of this being done that is all... :huh:
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The above graph is just with a 007p and remap, 205bhp & 245lb/ft :evil:
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The above graph is just with a 007p and remap, 205bhp & 245lb/ft :evil:
Lol - mine put out more when it was standard :tongue:
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diesels have lots of torque because........... well they have to have something going for them
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diesels have lots of torque because........... well they have to have something going for them
:grin: :grin:
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diesels have lots of torque because........... well they have to have something going for them
Aside from really low fuel consumption....
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diesels have lots of torque because........... well they have to have something going for them
Aside from really low fuel consumption....
till you turn them up :evil:
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diesels have lots of torque because........... well they have to have something going for them
Aside from really low fuel consumption....
Well spotted Quincy, nothing gets by you :grin:
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You took the thread down the 'what have the Romans ever done for us' direction.
Set them up and there's no way I'm not going to knock them down.
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Well apart from huge torque, and great fuel economy...
:laugh: :laugh:
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Had a MK4 TDi mapped and it made silly torque - LOVED IT
350z - hated the lack of torque and the whole petrol plague of having to rev the balls off of it. Got bored as a result.
Now the A4 with plenty of torque and I love every time I drive it :evil:
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need 2 stroke diesels FTW
make even more torques and they make nice noises like they are reving
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need 2 stroke diesels FTW
make even more torques and they make nice noises like they are reving
You mean like this one? http://youtu.be/m48vyc5beNg (http://youtu.be/m48vyc5beNg)
3424hp! :shocked: