Torque Cars

Why do diesel engines have so much Torque

Discussion in 'Diesel Chat' started by wizzer, 2 October 2015.

  1. wizzer

    wizzer Road Burner

    Messages:
    371
    From:
    Lyndhurst, Hampshire
    Car:
    VW Golf 2.0 TDi
    Why do diesel engines have so much Torque?

    Could petrol engines be tuned the same way to give loads of low end torque and power?
     
  2. crowley

    crowley Torque Junkie

    Messages:
    154
    From:
    Grampian
    Car:
    MyBotchedHeap
    Because their all turbocharged! I think...
     
  3. Aerial Andy944

    Aerial Andy944 The Torque Meister

    Messages:
    1,705
    From:
    Sunny South Somerset UK
    Car:
    VW Golf GT TDi 200
    Good question. It's something to do with the burn rate which is why they don't rev very high. I'm sure our diesel guru Hdi will be along soon to give a more detailed answer
     
  4. crowley

    crowley Torque Junkie

    Messages:
    154
    From:
    Grampian
    Car:
    MyBotchedHeap
    Diesel burns, petrol explodes.
     
  5. crowley

    crowley Torque Junkie

    Messages:
    154
    From:
    Grampian
    Car:
    MyBotchedHeap
    Diesel bad, petrol good.
     
  6. obi_waynne

    obi_waynne Administrator Staff Member Moderator

    Messages:
    41,128
    From:
    Deal, Kent UK
    Car:
    A3 1.4 TFSI 150 COD
    Vw diesels - very bad ;)
     
  7. HDi fun

    HDi fun TC ModFather

    Messages:
    15,384
    From:
    Buckinghamshire UK
    Car:
    Passat 2.0 TDi
    Waynne, it's not the VW engines I dislike, it's the thing they're bolted to, namely the rest of the car !!!

    The primary reason for diesel engines' torque characteristics are due to high BMEP (Brake Mean Effective [cylinder] Pressure). Compression ratios are typically 18:1 or higher. Naturally aspirated diesels can run as high as 24:1 !! Turbo-charging does contribute enormously to the torque delivery, as it does with a petrol engine.

    Burn rate forms part of it, too, but this is more to do with lower rev limits than low end shove. Put simply diesel does not burn quickly enough for the framefront to exert downward force on the piston crown as revs rise. The piston is effectively running away from the flamefront so this is a kind of self imposed rev limiter. Of course bore/stroke and many other factors are at work here but diesel does burn differently from petrol.

    @crowley - diesel bad? That's a bit of a sweeping statement. What do you mean?
     
  8. obi_waynne

    obi_waynne Administrator Staff Member Moderator

    Messages:
    41,128
    From:
    Deal, Kent UK
    Car:
    A3 1.4 TFSI 150 COD
    I was thinking more of the emissions scandal!
     
  9. HDi fun

    HDi fun TC ModFather

    Messages:
    15,384
    From:
    Buckinghamshire UK
    Car:
    Passat 2.0 TDi
    It appears it only applies to post '09 models. I am still of the opinion that it's fuss over nothing. If the cars are driven to the test prescription then they will achieve the official figures. We all know that these things vary hugely according to usage and driving style.

    I'm still struggling to understand the NOx issue anyway. What's the problem with NOx? It's just governmental nonsense. As yet we have no evidence that climate change exists anyway.
     
    Ronbros likes this.
  10. obi_waynne

    obi_waynne Administrator Staff Member Moderator

    Messages:
    41,128
    From:
    Deal, Kent UK
    Car:
    A3 1.4 TFSI 150 COD
    The cars need to be driven with no steering inputs to achieve the economy and emissions tested for. ;)
     
  11. Yugguy

    Yugguy Torque King

    Messages:
    4,789
    From:
    Rugby (expat Preston lad)
    Car:
    Merc C220Cdi Elegan
    Isnt nox poisonous tho? bad for the lungs?
     
  12. HDi fun

    HDi fun TC ModFather

    Messages:
    15,384
    From:
    Buckinghamshire UK
    Car:
    Passat 2.0 TDi
    So is CO2 yet the planet depends upon the stuff. It's possible that we interfere too much. There's only so much fossil fuel left and once it's gone it's gone. Probably not enough to destroy the planet, so no problem there directly.

    We should embrace nuclear in my opinion.
     
    Lunchmoney and Ronbros like this.
  13. obi_waynne

    obi_waynne Administrator Staff Member Moderator

    Messages:
    41,128
    From:
    Deal, Kent UK
    Car:
    A3 1.4 TFSI 150 COD
    Nuclear cars, that would be awesome. Loads of power on tap!
     
    Lunchmoney likes this.
  14. HDi fun

    HDi fun TC ModFather

    Messages:
    15,384
    From:
    Buckinghamshire UK
    Car:
    Passat 2.0 TDi
    I hadn't quite got to the point of considering a reactor and steam driven generator under the bonnet but now you mention it .... :)
     
  15. obi_waynne

    obi_waynne Administrator Staff Member Moderator

    Messages:
    41,128
    From:
    Deal, Kent UK
    Car:
    A3 1.4 TFSI 150 COD
    Throw in a flux capacitor for good measure and you'll never be late again!
     
    Lunchmoney likes this.
  16. Aerial Andy944

    Aerial Andy944 The Torque Meister

    Messages:
    1,705
    From:
    Sunny South Somerset UK
    Car:
    VW Golf GT TDi 200
    Yeah you'd have loads of power.........once!! Use it wisely :D
     
  17. Aerial Andy944

    Aerial Andy944 The Torque Meister

    Messages:
    1,705
    From:
    Sunny South Somerset UK
    Car:
    VW Golf GT TDi 200
    I'm quite liking my diesel (sorry Os) at the moment. Easy and refined just cruising aound and a big shove back into your seat out of the corners when you need to get a move on. Not as exciting as a screaming petrol engine but satisfying nonetheless. I must be getting old ?-/
     
    TCJBOLDIE, Ronbros and obi_waynne like this.
  18. Ronbros

    Ronbros Torque Junkie

    Messages:
    242
    From:
    USA Austin tx.
    Car:
    opel-isuzu 1.8 turb
    diesel engine torque is higher than petrol,it has more BTU energy, simply(like HDI said), because of its slower combustion burn rate, therefore expansion pressure pushing the piston, lasts longer on the power stroke!
    (one of the reasons why hi-octane petrol burns slower,longer push time).

    most petrol engines have spent/used effective pressure,by 90/100* crank angle after TDC.
    where as diesel expansion pressure can be carried as far as 160/170* crank angle after TDC.

    diesel has higher comp.ratio gives more expansion pressure, old design diesel engines had to be built heavy and strong, modern engineering(mainly EFI), has made them lighter and quieter!
     
    Last edited: 22 February 2016
    Lunchmoney and obi_waynne like this.
  19. HDi fun

    HDi fun TC ModFather

    Messages:
    15,384
    From:
    Buckinghamshire UK
    Car:
    Passat 2.0 TDi
    I wouldn't say that they're any less strongly built, it's more of a case of petrol engines now being built to similar levels of ruggedness as a concurrent diesel engine. Historically diesel engines would outlive petrols, this is no longer the case.

    Common rail EFI with multiple injection phases absolutely is the big contributor to refinement.

    What Ronbros says about expansion pressure is bang on ( :) ). It's also the reason for diesel engines' much lower rev limit compared to petrol ones.

    I like diesel's low revving shove, yet I think the flexibility of a petrol engine (especially with forced induction) probably is the better arrangement. Much easier to drive at low speed and free revving when required.
     
    Lunchmoney, obi_waynne and TCJBOLDIE like this.
  20. old-git

    old-git Moderator

    Messages:
    9,178
    From:
    Essex
    Car:
    Elan & Robin Hood
    Just noticed this.

    Wrong, both burn. However, petrol will explode if the mixture or timing is wrong. You can hear it as a pinking noise.
     
  21. HDi fun

    HDi fun TC ModFather

    Messages:
    15,384
    From:
    Buckinghamshire UK
    Car:
    Passat 2.0 TDi
    It's a horrible a noise. I owned a couple of Austin/Rover Montegos in late 1908s/early 1990s. They made that horrible rattly sound all the time. O series and S series engines weren't the best but even so it was not pleasant.
     
  22. WLBjork

    WLBjork Road Burner

    Messages:
    452
    Car:
    Octavia vRS LE
    Just as long as Bethesda don't design them.

    Cruddy things that explode as soon as you look at them funny...
     
  23. Ronbros

    Ronbros Torque Junkie

    Messages:
    242
    From:
    USA Austin tx.
    Car:
    opel-isuzu 1.8 turb
    what is Bethesda?
     
  24. WLBjork

    WLBjork Road Burner

    Messages:
    452
    Car:
    Octavia vRS LE
    A video games company. They own the "Fallout" franchise, which is based on a 1950s view of the future, after a nuclear war between the US and China.

    Link: - about 18 mins in to see what I mean. Yes, those cars are nuclear powered...
     
  25. HDi fun

    HDi fun TC ModFather

    Messages:
    15,384
    From:
    Buckinghamshire UK
    Car:
    Passat 2.0 TDi
    It's also a town in North West Wales.
     
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