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-   -   Do Diesel engines generate more Torque than Petrol engines? (https://www.team-bhp.com/forum/technical-stuff/101417-do-diesel-engines-generate-more-torque-than-petrol-engines-13.html)

If torque is related to displacement, then among both the engines with identical construction, it is the petrol one which should have more torque:)

As regards to NA engines, older engines were indeed poor in output vs petrol but then the petrol motors are newer designs. We should compare modern NA diesels of similar age as petrols.

Turbocharged engines ? Linea 1.4 Turbojet makes 205Nm, quite close to the 207Nm of the 1.3MJD. The Porsche 911 Turbo is also a torque-monster, 620Nm on the 997 generation with 3.6 liter engine. When it comes to turbocharging, diesels can take more advantage of the forced induction. Petrol motors are limited in how much boost can be applied since compression heats the air, and that cause premature ignition of the air-fuel mixture. Diesel is more thermally tolerant, hence higher boost pressure can be used , even NA dies engines have compression rations of 18-22 while petrol engines rarely go past 11, except high performance engines like sport-bikes and F1.

To sum up - petrol has higher calorific value (more combustion energy) but diesels are able to compensate, and exceed, cylinder pressures using higher compression ratios.

Diesels need higher compression = tough engine build = engine can be lugged = torque-y feeling?

@ramzsys : Torquey feeling is refers to engine response at low RPM with high throttle input, the engine's build has nothing to do with it.

It's not that diesels are torquey vs petrols, it's more about design-time decisions abput the operational use. Diesels are used for heavier vehicles more, hence low end torque definitely helps, plus the heavier components of diesel engines mean revving high puts more stress on it, thus diesels are usually designed to rev less and produce more useful output (torque) at lower RPM compared to petrols, whose lighter build also allows easier revving and higher peak RPM for the same forces/stress. But there are some petrol engines that are designed with low end torque bias. Take the Suzuki Bandit 1250cc engine, or the Honda Goldwing 1832cc V6 or Triumph Rocket III as the most extreme example of low-end biased petrol motors. The Triumph's 3 cylinder 2300cc engine makes 140hp - similar to 1.8-2.0 litre car engines, but is reportedly so torquey it will outrun 180hp sportbikes from 0-100.

So it's not that petrol engines can't be torquey, it's just that most such applications require a small light engine with high power, that means higher revving and more mid-range or top-end biased petrol motors are much more common.

even if you could do what you are suggesting, at a given rpm the petrol will have both higher torque and power.

However see below -

it is probably true that it is easier to turbocharge diesels vs. petrol. Also achievable CR is also higher for diesels (though that doesn't make as much a difference as you would think) So insisting on comparing NA diesel with NA petrol is not truly fair.


Actually on a per-unit volume basis diesel has significantly more calorific value. On a per unit weight basis both petrol and diesel are within 2% of each other.

As far as net energy delivery per stroke (and hence torque) are concerned - higher CR doesn't help all that much if you can't burn either more fuel or more energetic fuel.


This is not true even for everyday cars - when people talk of excellent pickup at high speeds (or easy overtaking in higher gear), they are essentially talking about high torque - even at pretty high rpm

Actually historically diesel engines have been used in commercial heavy duty applications and the reasons were entirely commercial - engine is more expensive but that is a one time cost, fuel is cheaper (even without subsidies it is cheaper if your engine is utilized all the time) and large commerical engines can use the cheapest of waxy crap.

A petrol engine will have no problem providing you similar low-end torque. The low end torque of most petrol hatches in the Indian market is usually similar or better than their diesel counterparts even though their displacement is invariably less than diesel versions, this is in particular because the magic of trubocharger is not available at low rpm.

Peak torque of diesels is higher, but frankly if you want to talk about "low end torque"let's talk in sub-1000rpm range.



First of all for similar breathing equipment (trubo etc.) and similar displacement, you will find that petrols invariably have higher torque at a given rpm than their diesel counterparts - even with benefits of higher CR accruing to diesels only. Second torque at the wheels is not directly related to torque at the shaft - gear ratio can increase or decrease it. So it is cheaper in petrols to design a smaller higher rpm engine and then use gearing to reduce rpm at wheel and increase torque.

In a diesel the higher-rpm option is not even available (heavier construction and slower burning fuel, both play a part), so higher displacement is almost always required.

After reading through so many posts, I still do not understand where the discussion has led to. Has it been ascertained that diesel engines produce more torque or don't they?

While we are comparing diesel vs gasoline, what are the parameters which are same or different for this evaluation. I know fuel is different, but what else?

Spike

The simple conclusion is that for practical comparisons i.e. hatches/sedans/MUV of same make available with a choice of both engines ,diesels generate more torque!

The petrols could be turbocharged and tuned for more torque but its not economically viable.

Am i Wrong?

At least you have read through (I assume all) the posts. Unlike most others who read maybe the last two posts and then shoot from the hip!

You need this discussion to tell you what is what?!

I think everyone 'knows' the answer. Does it need discussion?


Regards
Sutripta

Not all, if I read all, I will loose whatever little I know.:confused:

Perhaps, I could learn something new, just like the Carnot thingy.

Yeah everyone knows, but the answers are still unclear, at-least for me.

Spike

Lets take a look at modern engines from the same manufacturer.

A BWM N13B16 engine found in 1 series is a 1.6L petrol engine with 168 hp @4800rpm and 250 N·m @1500–4500rpm

Compare it with the BMW N47D16 engine also found in the 1 series is a 1.6L diesel engine with 114 hp @4000rpm and 260 N·m @1750–2500rpm

or
VW 1.4 liter TFSI petrol engine 177 bhp @ 6,200 rpm and 250 N.M @ 2,000 - 4,500 rpm

Compare that with VW 1.6 liter TDI-CR diesel engine 114 bhp @ 4,400 rpm; 250 N.M @ 2,000-2,500 rpm

So from what i see, if you turbo charge a modern engine the torque figures are more or less the same but the petrol engine will still make the most horse power.

Put very simply indeed:

Usually an engine which heats air by compression to ignite an oil vapour is always stronger than one which relies on a spark to ignite a gas or vapourised liquid fuel. But conversely a gas or petrol engine with spark plugs to explode the mixture is usually able to spin faster so develop more power. Think big-muscled Romanian shot-putter compared with puny 100m sprinter.

Traditionally, a petrol engine has a high top speed but has relatively little torque/twisting power and so will not be able to pull much of a load without many gears and high revs. A torque-strong diesel will easily pull a lot of weight and accelerate rapidly low down in the revs and only to a relatively low top speed.

Electronics and exhaust supercharging have improved the power of the diesel engine - also the compression-ignition and spark-ignition engines have begun to combine their strengths.

Choose a modern turbo-diesel for the cut and thrust of congested road motoring and a petrol engine for refinement and high top speed - the racetrack.

I love the old-school diesel for its tractability, toughness and simplicty - if it is turning and there is fuel and air, it will run. With a petrol engine you need electricity, a spark and everything which is needed to make that spark appear at just the right moment. Damp, poor wiring, problems with the condensor or points, igntion coil or multiple sensors make a petrol engine dead.

Thanks for those figures, they look useful. But is the torque figure above correct?

Keeping aside turbocharging, what happens if both the engines have same geometrical parameters like bore, stroke etc and are NA, and why?

Spike

[quote=SPIKE ARRESTOR;3111790

Keeping aside turbocharging, what happens if both the engines have same geometrical parameters like bore, stroke etc and are NA, and why?

Spike[/quote]


A petrol engine will produce more power because it can rev faster.

Yes those figures are correct.Both those companies petrol engines are turbocharged just like their respective diesel engines.

The petrol engine will produce more power by a big margin as to why its answered by tbhp member FlatOut.

With respect to the thread title, personally, I am happy that my humble intellect could make much meaning out of this thread from these particular posts.

1.
2.

If we could arrive at some conclusion with the above figures, maybe, we can start looking into why exactly? Or is it the other way round? Reasons leading to conclusions?