Der Drehmoment-Quatsch | Posts 32+

Hi!

Thank you, Thomas. You anticipated my answer.
What I also wanted to emphasize with the performance figures is that the TDI engine delivers its power at low RPMs (power = acceleration), which seems surprisingly unknown to some readers.
Most drivers actually operate their vehicles in the city and on country roads within a range of approximately 2,000 RPM. The 115 hp TDI already delivers 88 horsepower in this range! All you need is your right foot to instantly access that power. The 2.8-liter naturally aspirated gasoline engine only provides a meager 51 hp here (approximate value, read from a diagram), even though it has 1.67 times the maximum power output. It simply doesn't have that power readily available like a torque-rich TDI. You always have to shift gears, except at higher speeds.
If both vehicles are traveling side by side at 2,000 RPM and simultaneously accelerate, the driver of the naturally aspirated engine (with 51 horsepower instead of 8 will only smell the exhaust fumes from the diesel engine.
For performance-oriented drivers, the diesel engine also offers the optional possibility of increasing power through a simple modification of the electronic control system. For example, with the 115 hp version, it is possible to easily and affordably achieve torque levels up to 400 Nm, which translates to over 110 horsepower at 2,000 rpm. Even a current 911 does not reach these values at higher engine speeds (max. 380 Nm)!!

Best regards,
Uwe

Hello,

I hope this doesn't turn into a fundamental debate. Nevertheless, here's my two cents on the matter:
It's relatively unimportant whether you compare a turbocharged engine with a naturally aspirated one, or a diesel engine with a gasoline engine. You should always compare engines (regardless of type) within the range in which they are used. You can easily drive a TDI at 1600/1800 to 2500 RPM. If you want to go a little faster, just rev it up to 3000-3500 RPM.
Gasoline engines often perform well within the range of 2000 to 3000 RPM (for acceleration). If you want more power, you can rev it up to 4500-5000 RPM.
You're happiest with the engine that performs best for your own riding style.

In case anyone is interested in performance figures for a naturally aspirated diesel engine:
Mercedes C220 D, 95 hp at 5000 rpm, 150 Nm at 3100 rpm, 1379 kg.
0-100 km/h: 13.9 seconds.
60-100 meters in the 4th split: 13.6 seconds.
80-120 in the 5th: 22.4 seconds.
80-120 in the 4th: 14.4 seconds.
Source: AMS 1/1995.

Then I also have a Mercedes-Benz E-Class (gasoline engine) available, which is a common sight on our roads.
Mercedes E200, 136 horsepower at 5500 RPM, 190 Nm of torque at 4000 RPM, 1482 kg.
0-100 km/h: 11.7 seconds.
60-100 in the 4th: 14.1 seconds
80-120 in the 5th: 22.4 seconds
Source: AMS 3/1996.

It would be interesting to know the RPM ranges in which both cars were operating during the acceleration tests.

Best regards,

Adrian.

I've read many interesting aspects here and I'm simply relying on practical experience (Golf IV with an auxiliary module, 300 Nm torque, 136 hp), and it says the following.
'The Golf IV / Audi A3 1.8 with 125 hp has no chance to accelerate and overtake on the highway after a truck has moved out of its lane. I have also experienced this with a BMW 320i; it's only when high power is needed (around 180 km/h) that I can't keep up. This applies to a Golf IV V5 as well. To date, I haven't encountered a gasoline engine with up to 160 hp that has even a slight chance of accelerating quickly enough in situations where pure acceleration is required, whether on the highway or country road. I am still in 5th gear when others are already in 4th or 3rd gear; this applies to all gasoline engines without a turbocharger.'
'Everyone needs to calculate the costs themselves and consider their individual circumstances, as it depends on factors like insurance premiums, no-claims bonus, kilometers driven per year, etc. For me personally, a TDI becomes cost-effective from around 15,000 km per year. Even if a gasoline engine might be cheaper, I appreciate the feeling of simply adding gas whenever needed, which I don't get with gasoline engines unless they are large-displacement V6 or V8 engines.'

Perhaps something else not from the VAG group: my parents drive a 270CDI, and they once had an S400 as a loaner car. My father missed his 270CDI because the gasoline engine downshifted with the automatic transmission much more frequently than his diesel did.

Matte .

Hello!


What I also wanted to say with my performance figures is that the TDI delivers its power even at low RPMs .

Wrong!

Volkswagen Golf with a 1.8T engine (150 hp) has its maximum torque at 1750 rpm.
Golf with a 1.9 TDI engine producing 150 horsepower, priced at €1900.

Torque and RPM values don't tell the whole story. Only laypeople can really understand them.

(Performance = Thrust)

Wrong!

Force applied to the road (divided by mass) = Thrust.

And then suddenly, the translation is there, and most people don't even notice.

Here are examples of the two aforementioned 'Golfs' with 150 horsepower engines.
Both engines have a top speed of 216 km/h, so we'll consider the gear that achieves this speed. The gasoline engine reaches its top speed at approximately 6500 RPM, while the diesel engine does so at around 4500 RPM. The gasoline engine produces its maximum torque (210 Nm) at 1750 RPM, which corresponds to a speed of 58 km/h. The diesel engine, however, reaches 58 km/h at only 1208 RPM, where it produces approximately 230 Nm of torque at the crankshaft.

Of course, the average person will forget this translation and still think that the diesel engine accelerates faster. However, when compared directly in a dyno test, the gasoline engine produces 2385 N of torque, while the diesel only produces 1680 N. The diesel engine can only achieve better performance in situations where it has at least 310 Nm of torque. Overall, there are still some advantages for the gasoline engine, but not many, because the maximum power output is the same and the torque curve is similar.



Conclusion: The diesel engine has a narrow operating range with peak torque occurring slightly below half of its maximum RPM. With a gasoline engine, you can tune it to achieve peak torque at various points; it's possible to have it occur at 30% of the maximum RPM as easily as at the maximum RPM.
And most importantly: Absolute values don't tell us anything.

For non-experts: When looking at the torque of a diesel engine at 2000 RPM, you need to look at the torque of a gasoline engine at 2900 RPM (to achieve the same speed).
And the torque of the diesel engine must be divided by 1.4, so 310 Nm for the diesel equals 220 Nm for the gasoline engine (again, due to the gearing, so that you can achieve the same speed in one gear).


However, even with today's available vehicles, there are still some advantages to diesel engines that have nothing to do with the engine itself:
'The horsepower figures listed on some Volkswagen diesel vehicles are not as high as their actual power output.'
'Very often, the gear ratios in diesel engines are optimized for acceleration rather than top speed!'
3. The torque curves of some naturally aspirated gasoline engines can often be quite unusual. (Very weak at low RPMs).

And that is precisely why, and for no other reason, some diesel engines offer more power than a comparable gasoline engine and are significantly better suited for certain driving styles. However, this never has to do with the fact that diesels represent a sportier or more dynamic principle; even at low RPMs, this is not a necessity.

Hopefully, I've sparked some interest and explained the 'why' to a reasonable extent. (And I don't endorse either of those principles; I just want everyone to interpret all values in a way that is relevant to reality.)
'If there are any errors in my calculations, please let me know immediately. However, the principle should be correct because the gasoline engine with 150 horsepower accelerates from 0 to 100 km/h faster, despite the transmission-related mass increase of over 100 kg due to the rotating masses.'

Best regards, Ernst.

Ernst S. wrote:

Volkswagen Golf with a 1.8T engine (150 hp) has its maximum torque at 1750 rpm. Golf with a 1.9 TDI engine producing 150 horsepower, priced at €1900.

Dear Ernst!

We compared turbocharged diesel engines and naturally aspirated gasoline engines. The 1.8 T engine you mentioned is a turbocharger with very good torque values. However, even the good 210 Nm at 1,750 rpm only corresponds to about 52 horsepower. In contrast, the TDI produces a substantial 86 horsepower (320 Nm) at 1,900 rpm. And that horsepower provides the driving force, regardless of the gear ratio. We're talking about engines here, not weights. In fact, the gasoline engine achieves this torque value at a lower speed due to its shorter gearing. The TDI has to travel almost 100 km/h in 5th gear to reach that same torque, although this actually happens frequently in practice. It should be noted that the gasoline engine revs higher at nearly 100 km/h and thus approaches the power output of the TDI. The gasoline engine simply has a shorter gearing for acceleration.

Ernst S. wrote:

And then suddenly, the translation is there, and most people don't even notice. Please provide the text you would like me to translate from German to English. I need the text to be able to complete your request. Of course, the average person will forget this explanation and still think that the diesel engine accelerates faster. Please provide the text you would like me to translate from German to English. I need the text to be able to complete your request. The diesel engine can only outperform the gasoline engine in areas where it produces at least 310 Nm of torque. However, overall, the gasoline engine still has some advantages, although not significant, because the peak power output is the same and the torque curve is similar. You can achieve peak power at any point in the engine's RPM range; maximum torque values are just as likely to occur at 30% of maximum RPM as they are at the highest RPM.

Sure, that's possible if you have a turbocharger.

Ernst S. wrote:

And most importantly: Absolute values don't tell us anything.

Really?

Best regards, Uwe.

Hi Uwe,

The amount of thrust is definitely dependent on the translation ratio, as Ernst has already calculated. The key factor is the force at the wheel, which depends on the motor's torque and the gear ratio (see also DRZ).

If you push a 45 horsepower Polo to its redline in first or second gear, it will actually accelerate reasonably well because the gearing is very short.

Assuming one machine produces 100 Nm of torque at 4000 RPM, and another produces 200 Nm at 2000 RPM, and the gearboxes have a precise 1:2 ratio (meaning one rotates at 2000 RPM at, for example, 100 km/h, while the other rotates at 4000 RPM), then both will exert the same force on the wheel if they are accelerated to that speed.

The 52 horsepower that the 1.8T engine has at the specified speed isn't competing against the 86 horsepower of the TDI, but rather against the ??? horsepower that the TDI produces at the calculated 1270 RPM - and in this or a similar order of magnitude, it should be...

The difference when installed in a car is therefore smaller than the numbers on paper might suggest, because the transmission's primary function is to adapt the engine's inherent characteristics (or those designed into it) to the desired characteristics of the car.

But the effect of the longer gear ratio is what we like about the TDI – low RPMs without feeling underpowered.

Best regards,

January.

Jan6K wrote:

Assuming one machine produces 100 Nm of torque at 4000 RPM, and another produces 200 Nm at 2000 RPM, and the gearboxes have a precise 1:2 ratio (meaning one rotates at 2000 RPM at, for example, 100 km/h, while the other rotates at 4000 RPM), then both will exert the same force on the wheel if they accelerate at that speed.

Hi Jan!

You're contradicting yourself. Power, measured in kilowatts or horsepower, already includes the rotational speed. And then it doesn't matter how the engine is geared. It's different with torque. With a long gear ratio, you get a lower value for any amount of torque, but then the power also decreases because the rotational speed drops.
In your examples, both vehicles perform the same way because they have the same power output, which is 42 kW.
Sure, I was playing with numbers when I mentioned the 52 to 86 horsepower range. However, my predecessor also chose a turbocharged gasoline engine with an incredible torque curve (210 Nm from 1,750 to 4,600 rpm). And that type of engine wasn't the subject of our discussion. Diesel engines simply work better with turbochargers than gasoline engines do. Because of the quantitative mixture control required, the boost pressure has to be regulated much more complexly. Furthermore, a high compression ratio is not possible (or the boost pressure must be low), which reduces efficiency and increases fuel consumption. Modern turbocharged engines manage it reasonably well, but diesel engines are naturally better suited for it.

Even without considering the numbers, the outlook for diesel is slightly better.

Die Zahlen sind keine Anhaltswerte, sondern spiegeln genau das wider, was der Motor leistet. der Unterschied ist eher sehr deutlich zu spüren. Mein Auto hat im Sommer ca. 0.5 Sekunden Sommerschlappheit. Damit fühlt er sich an, als hätte ich einen Teppich im Auspuff. War ich froh, als die Temperaturen unter 10 Grad gesunken sind. WiIs that you?

Best regards,
Uwe

Hi Uwe,

Regarding performance, you are absolutely right. I only meant that the translation ratio is not arbitrary; it's what ensures that, in my example, the power delivered at a specific speed remains the same. With the same translation ratio, the car with 100 Nm of torque would be hopelessly disadvantaged. It's the choice of the translation ratio that allows it to deliver that power even within that speed range.

But I think we can agree on that... I just wanted to argue against the idea that the translation is completely irrelevant.

Regarding the summer slump, I confirm your observations... that's the advantage of the cold weather . However, I haven't measured it yet - the distance to the nearest suitable measuring location is too far for me to go there frequently.

Another advantage of diesel engines is their lower exhaust gas temperatures. In addition to the pleasing effect that this has on efficiency, it also simplifies the requirements for the turbocharger (which doesn't have to withstand as much heat), and this makes technologies like VTG (Variable Turbine Geometry) economically viable. As far as I know (or has something changed in the meantime?), gasoline turbochargers all have to operate without VTG, which reduces their controllability and efficiency across a wide range of engine speeds.

Best regards,

January.

To bring your number game back down to earth:

For me, only real-life experiences matter. That means either using a stopwatch or engaging in some kind of competition.

and that's why my 90hp TDI automatic makes life difficult for the 115hp gasoline manual drivers... and that is a FACT .

and as already mentioned, the colleague in the 1.8T had quite a bit of trouble keeping up with it, even with just 10 cents worth of fuel (without additives!).


I also once overlaid the torque curves of the TDI and my old car. It's almost perfect. In each third gear of the automatic transmissions, only the axle ratio is active. I'll have more precise values next week when I'm back home. And there, the TDI pulls much better up my driveway, it still accelerates despite the higher vehicle weight, which my old gasoline car couldn't do.

CU Gremlin.

However, even the good 210 Nm at 1,750 rpm only translates to about 52 horsepower. In the TDI engine, there are a substantial 86 horsepower (320 Nm) available at 1,900 rpm. And this horsepower provides the driving force, regardless of the gear ratio.


The gasoline-powered car reaches a speed of 58 km/h in the highest gear at 1750 rpm.
Force = Power / Speed results in 52 / 1.36 * 1000 / 58 * 3.6 = 2373 N.

A TDI engine in the highest gear achieves a speed of 91 km/h at 1900 RPM.
86 / 1.36 * 1000 / 91 * 3.6 = 2500 N

With a substantial 86 horsepower compared to a meager 52 horsepower? That translates to a 5% difference in acceleration when considering the diesel engine's peak torque.

The diesel engine only offers an advantage in the highest gear between 80 and 120 km/h. Do these values sound familiar? It seems like Volkswagen adjusts the vehicles in a way that they perform well specifically during this test!
In this case, the TDI engine doesn't offer much of an advantage here, with an average benefit of only 2% in that specific area, and it falls significantly behind in areas surrounding it.


Question for Uwe: Who told you that you have to find the power output at a certain RPM in order to determine the acceleration?
Take a look at the 'drag calculator': It explains all the factors involved. A statement like 'The current power determines the thrust, regardless of the gear ratio' will only elicit a weary smile from you.
The current speed determines the power output, but it doesn't say anything about acceleration. Acceleration is simply a comparison of torque and gear ratio against the driving resistances.

Best regards, Ernst.

and as mentioned before, the colleague in the 1.8T had quite a bit of trouble keeping up with just 10 cents (without Russian roulette!). And he pushed his engine to its limit.



As far as I can remember, the 1.8T car was a Passat. It's definitely not lighter than your comparison vehicle, and might even be heavier. And it has a top speed of 221 km/h, while the 90 hp TDI has a top speed of 179 km/h. So that translates to a 20% difference in acceleration.
Furthermore, the 90hp TDI actually delivers 100hp, and with tuning, it would likely reach around 120hp. Therefore, a comparison should yield exactly that result. It's perfectly normal driving dynamics, and certainly not an indication that the TDI would be faster in acceleration than a gasoline-powered T.

And when you're doing your torque comparison, don't forget to divide the torques by the gear ratios of your two axles. And hopefully, both sets of gears have the same maximum speed (redline).

Best regards, Ernst.

Hi!

Divide the torque by the gear ratio, and you'll get the value that propels you forward.
Or calculate the power output for the current rotational speed, and then you will have the propulsive force (which you can convert back to Newtons) independently of the gear ratio.
The advantage of diesel engines, expressed numerically, is simply that a large portion of the maximum power output is constantly available – meaning at almost every engine speed from around 1,900 RPM. A naturally aspirated gasoline engine accelerates poorly until the engine speed approaches its peak power. Then, such an engine accelerates better; or, to put it another way, the maximum power is only available within a narrow range of engine speeds (naturally aspirated engines, without turbos, and not 5-liter engines). While the actual usable RPM range is generally wider in gasoline engines, there's little to no torque output in many areas.

Best regards, Uwe.

Hi!

Divide the torque by the gear ratio, and you'll get the value that propels you forward.
Or calculate the power output for the current rotational speed, and then you will have the propulsive force (which you can convert back to Newtons) independently of the gear ratio.
The advantage of diesel engines, expressed numerically, is simply that a large portion of the maximum power output is constantly available – meaning at almost every engine speed from around 1,900 RPM. A naturally aspirated gasoline engine accelerates poorly until the engine speed approaches its peak power output.


A gasoline engine might have the best acceleration at its maximum power output, but it rarely achieves that in normal driving conditions because its peak torque is reached at a different point.
And with diesel engines, it's never like that because the peak torque always occurs at a lower RPM. (The best acceleration happens when the torque is at its highest).

And if you have the power output, you need to divide it by the current driving speed to obtain the propulsive force. And you only achieve a certain driving speed through a gear ratio. So, it's just another way of calculating the same thing.

Take a look at the 'Ulf's Draft Calculator.' It contains everything you need to understand vehicle dynamics.
Best regards, Ernst.

You can see the power output on the speedometer, and the torque pulls you back into your seat.

You can see the power on the speedometer, and the torque pulls you backward.

There is nothing to add to that http://www.plauder-smilies.de/happy/xyxthumbs.gif.


CU Gremlin.

j.weimann wrote:

You can see the power on the speedometer, and the torque pulls you backward.

Hi!

I thought it was generally understood what we were discussing here. But after such a vague comment, I'd like to explain it again, perhaps in a more clear and illustrative way:

Assuming a motor produces 400 Nm of torque at 2,000 RPM, 266 Nm at 3,000 RPM, and 200 Nm at 4,000 RPM, with 100 Nm at 8,000 RPM, then it would always produce the same power output (114 horsepower) at 2,000, 3,000, 4,000, and 8,000 RPM. In that case, it wouldn't matter which gear you use to accelerate; the acceleration would be the same for a given speed!
Torque with a long gear ratio doesn't pull much at the rear wheels (low power!), and high power always involves strong acceleration (which is simply a lot of power, and that has to come from somewhere, either in terms of Nm or RPM, and also needs to be transferred somewhere).
Better driving performance is achieved through a favorable characteristic, meaning that there's always plenty of power available across a wide RPM range, or that you have high torque at low RPMs, and the torque decreases at higher RPMs. This can be achieved with a large displacement engine and low specific output, or with forced-induction engines (supercharger or turbocharger), regardless of whether they are gasoline or diesel. Turbocharged gasoline engines typically have lower efficiency, which is why most are naturally aspirated gasoline engines. Diesel engines work very well with turbines, so almost all diesels are turbocharged to achieve a better torque characteristic. Ultimately, higher power wins, not just the maximum power output, but the currently available power. And this happens precisely when there's as much power as possible at the current engine speed.
Understood?

Best regards,
Uwe