Horsepower vs torque

  • This topic has 16 replies, 5 voices, and was last updated 1 month ago by POPS.
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  • #141735 Reply
    Luke

    it’s a cliche topic there’s always debates to determine the difference. I’m aware that diesel cars have higher torque figure than a petrol so does that mean the diesel car has stronger mid range acceleration from speeds between 30mph-60mph and are quicker to overtake than petrol. Is horsepower a measurement of combination of acceleration and top speed, is that correct? I notice petrols are faster at higher speeds at higher Revv range .  For instance I drove 1.0 Audi A3 1.0 tfsi and bmw 1 series 116d 1.5 in the past on Motabilty  both have 116bhp I clearly noticed the bmw 116d is stronger for overtaking, mid acceleration  and it needs lesss gear changes.

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  • #141736 Reply
    Lou

    Going back a few years I went from a 2 litre diesel Q3 Quattro to a bmw 1 series 2 litre diesel….the bmw was faster on pulling power & overtaking and much much better MPG.

    #141747 Reply
    shaun

    lower horsepower but higher torque figures of a diesel mean they have a narrow band ( think rev range) where that torque is usable, but it is really usable like you state for overtaking, mid-range pull etc. the petrol with its higher horses but lower torque is spread out more over the rev range, meaning the torque is a lot more levelled out, less oomph or push you into your seat, but its higher horses mean a higher top-end speed.

     

    #141775 Reply
    Wigwam
    Participant

    Torque is turning power – it’s what spins the wheels when you take off.  Horsepower is energy – it’s what makes the car overcome wind resistance and friction losses to go fast.

    Traditionally naturally aspirated diesel engines produced more torque but less power than naturally aspirated petrol engines.  These rules no longer apply with modern forced charge computer controlled engines. The designer can to a great extent choose the engine characteristics.

     

     

    #141898 Reply
    Donkey Oatie

    Horsepower =Torque x RPM / 5252

    which is why horsepower and torque lines on a Dyno chart cross at 5252 rpm

    if you have an petrol engine producing 200bhp @ 8000rpm you would have 131.3 lb/ft torque

    if you have an diesel engine producing 200 bhp @ 5000rpm you would have 210.08 lb ft; torque

    so the diesel engine produces more “shove” at lower revs which is easier for normal driving. for ultimate performance a high revving petrol engine is better abut feels flatter at low revs and “peakier”

    #141909 Reply
    Wigwam
    Participant

    In theory Donkey Oatie, but not in fact. Turbo charged petrol engine:

     

    #141945 Reply
    Jamie

    I could be wrong but what I was always told, torque gets you there and the horses keep you there

    #141950 Reply
    Glos Guy
    Participant

    I haven’t got a clue about the technical explanations, but having had dozens of both petrol and diesel cars, diesels are far better in the mid range (torque). I would go so far as to say that in mid range acceleration a 2.0 diesel feels like a 3.0 petrol.

    #141955 Reply
    Wigwam
    Participant

    That was definitely the case, Glos Guy. Petrol engines had to rev much higher too,  but things have changed a lot with forced charge (turbo,) engines.

    #141995 Reply
    Tharg
    Participant

    As a matter of technical interest, what is the correct way to calculate power-to-weight ratio? Internet stuff says divide bhp figure by curb weight but, as Wigwam points out, torque is a factor too. So do you take an average of bhp/torque or is it more complicated?

    #141996 Reply
    Intranicity
    Participant

    Power to weight ratios, just make sure you compare the right units, metric or imperial.

    BHP divided by pounds or PS divided by kg, but that isn’t the full story as the drag coefficient and rolling resistance make a big difference too.

    Previous Motability Cars
    2006 - 2009 Skoda Superb VR6 2.0tdi
    2009 - 2012 Citroen C5 2.0tdi VTR Nav
    2012 - 2015 Nissan Qashqai 1.5dci tekna
    2015 - 2018 Ford Kuga 2.0tdi Titanium X
    2018 - 2021 BMW 220d X drive 2 Series Active Luxury
    2021- Hyundai Kona Electric Premium SE

    #141997 Reply
    Tharg
    Participant

    Thanks, Intranicity. Most helpful.

    #141998 Reply
    Intranicity
    Participant

    This article is quite good at explaining the relationship and difference between Horsepower and Torque

    https://www.caranddriver.com/news/a15347872/horsepower-vs-torque-whats-the-difference/

    Previous Motability Cars
    2006 - 2009 Skoda Superb VR6 2.0tdi
    2009 - 2012 Citroen C5 2.0tdi VTR Nav
    2012 - 2015 Nissan Qashqai 1.5dci tekna
    2015 - 2018 Ford Kuga 2.0tdi Titanium X
    2018 - 2021 BMW 220d X drive 2 Series Active Luxury
    2021- Hyundai Kona Electric Premium SE

    #141999 Reply
    Wigwam
    Participant

    As Intranicity says power to weight ratio is really a simplistic measure which can be good for comparing otherwise similar cars. Ultimately other factors like those he mentioned come into play.  However a 1 ton car with a 100hp engine is likely to go faster and accelerate better than a 2 ton car with a 150hp engine…

    #142000 Reply
    Tharg
    Participant

    Wigwam and Intranicity, many thanks again. Starting to understand a bit better now. The scientific definitions of power and torque are very helpful.

    #142002 Reply
    Intranicity
    Participant

    One big thing to consider though is how you drive a car, BHP figures are quoted at a set RPM, ie 190BHP @ 7200rpm.

    The big advantage of the high torque of a diesel engine is it tends to put in peak BHP at a much lower engine RPM, so you don’t continually need to drop down gears to overtake, if you consider your normal driving on country roads, it’s much less work (changing gears) in a car with higher torque than a car with massive amounts of BHP, but get on a track where the you can sit at high RPM more often, the BHP will probably be quicker.  With the advent of turbos being more common, the gap has closed.

    I currently drive a BMW with a 220d X drive engine, rarely ever goes over 3000 rpm even driving hard on country roads (The duel clutch 8 speed gearbox really helps) but this car produces 190BHP @ 4000RPM, 400Nm of torque and 6.9 secs 0-60, it’s so easy to drive fast on twisty winding roads, you’d struggle to overtake me even in a Ferrari, but get it on the track and it would be getting lapped pretty quickly.

    So, in many ways, for normal everyday driving, Torque is probably far more useful than BHP unless you really love revving the ass out of an engine and using the gears all the time.

    Previous Motability Cars
    2006 - 2009 Skoda Superb VR6 2.0tdi
    2009 - 2012 Citroen C5 2.0tdi VTR Nav
    2012 - 2015 Nissan Qashqai 1.5dci tekna
    2015 - 2018 Ford Kuga 2.0tdi Titanium X
    2018 - 2021 BMW 220d X drive 2 Series Active Luxury
    2021- Hyundai Kona Electric Premium SE

    #142009 Reply
    POPS
    Moderator

    I drive a (2017) BMW X1, X Drive 2.5 diesel which has 231bhp and 450nm of torque. I can confirm that its mid range acceleration is both powerful and seamless. It’s an engine that can keep you safe in most unexpected situations.

    However, I’ve thought back over the last four years and can only think of a few occasions when I’ve used that fierce acceleration. At my age and in my state of health I’m now going to change to something altogether more sedate and let technology lend me a hand instead of relying on sheer power.

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