[snoep]

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WHAT MAKES YOUR CAR FAST? THE DYNAMICS OF TORQUE AND HORSEPOWER

In discussions about car performance, the terms horsepower (expressed in hp or kW) and torque (expressed in Nm) often come up. But what do these terms really mean for a car's driving behavior and driving experience? Why does a turbodiesel with lots of torque sometimes feel quick, yet underperform at higher speeds? And why do Formula 1 cars with relatively little torque still deliver incredible performance?

In this article, I’ll explain using power and torque curves, practical examples, and insights from both engine technology and modern engine tuning.

TORQUE AND HORSEPOWER: WHAT’S THE DIFFERENCE?

Torque (Nm) is the rotational force produced by an engine. This determines how "strong" a car feels at a given rpm. Think of it like a lever: the more force, the easier it is to move something.

Horsepower (hp or kW) is the result of torque combined with engine speed (rpm). Horsepower determines how quickly a car can accelerate or build speed.

The formula for horsepower is:
Horsepower (hp) = (Torque (Nm) × RPM) / 7023

In summary:

Torque indicates how strong the engine is at a given rpm.
Horsepower combines this torque with how fast the engine spins (rpm).


Example:

An engine with high torque at low rpm delivers strong-feeling acceleration from a standstill.
An engine that revs high can still produce a lot of horsepower, even if the torque is relatively low.


1. POWER/TORQUE CURVES OF DIESEL TURBO ENGINES

In diesel turbo engines, you often see:

Torque: High peak torque at low rpm (typically between 1,500-3,000 rpm).
Horsepower: Due to the rapid drop in torque at mid-rpm (often starting at 3,500 rpm), the power curve flattens out.
Example: BMW G21 M340d (B57D30T2) before and after tuning



The torque peaks early but quickly drops off, causing horsepower to decrease at higher rpm.

1.1 EFFECT OF CHIP TUNING ON DIESEL TURBO ENGINES

Chip tuning increases boost pressure and optimizes fuel injection, resulting in more torque at low rpm. However, due to limited air supply, power still falls off at higher rpm.

2. POWER/TORQUE CURVES OF GASOLINE TURBO ENGINES

In gasoline turbo engines, you often see:

Torque: High and broadly available (e.g., between 2,000-5,000 rpm).
Horsepower: Flattens out at higher rpm (typically above 6,000 rpm) due to turbo limitations.
Example: BMW G20 M340i (B58B30TU) before and after tuning



Torque increases significantly at low rpm but flattens out at higher rpm due to turbo limitations.

2.1 EFFECT OF CHIP TUNING ON GASOLINE TURBO ENGINES

Torque: After tuning, torque increases significantly at lower rpm (from 540 Nm to 790 Nm in the example above).
[]Turbo limit: After mid-rpm, the turbos "run out of breath," causing torque to drop and the power curve to flatten.


3. POWER/TORQUE CURVES OF HIGH-REVVING NATURALLY ASPIRATED ENGINES

In naturally aspirated (non-turbo) sports engines, you often see:

Torque: Lower peak torque, but consistent across a broad rpm range.
Horsepower: Increases linearly to high rpm (often up to 8,000 rpm or more).
Example: BMW E60 M5 (S85B50) before and after tuning



Torque is relatively low but increases with rpm, keeping the power curve steep up to the redline. This results in a dynamic driving experience, but to accelerate quickly, you need to rev the engine high.

3.1 EFFECT OF CHIP TUNING ON HIGH-REVVING NATURALLY ASPIRATED ENGINES

In naturally aspirated gasoline engines, chip tuning has a smaller effect than in turbo engines because there is no turbo or supercharger to increase airflow. However, adjustments to fuel injection and ignition timing can still yield benefits:

Power gain: A small increase in horsepower. In the example the was almost 50 hp.
RPM limit: The rev limiter can often be raised from 8,250 rpm to around 8,500-8,600 rpm.
Throttle response: Improved throttle response for sharper acceleration.
The shape of the torque curve remains mostly the same, but peak power shifts slightly higher in the rpm range.

CONCLUSION

1. Turbodiesels
Acceleration from a standstill: Quick and strong due to high torque at low rpm.

100-200 km/h: Moderate, as power drops off at higher rpm.
Top speed: Limited by low power at high rpm.

Driving experience: Feels powerful at low rpm but loses excitement as torque and power drop off at mid-to-high rpm.

Use: Ideal for daily driving, city traffic, and efficient highway cruising.

2. Gasoline turbo engines
Acceleration from a standstill: Strong and smooth due to broad torque peak.
100-200 km/h: Good, with power available over a wider rpm range.

Top speed: High, depending on turbo size and boost pressure.

Driving experience: Dynamic acceleration at low and mid rpm, but turbo limitations reduce power at very high rpm.

Use: Versatile for sporty street and track use. Similar to modern Formula 1 engines with high-boost turbo systems.

3. High-revving naturally aspirated engines
Acceleration from a standstill: Moderate at low rpm, strong at high rpm.

100-200 km/h: Excellent, due to high power at high rpm.

Top speed: Very high, with power continuing to rise up to the redline.
Driving experience: Linear power delivery and an exciting, dynamic experience as rpm increase.

Use: Perfect for track use, where linear power and high rpm are essential.

SUMMARY

Turbodiesels: Great for quick starts and strong low-rpm performance but lose steam at high rpm. A turbo upgrade can help sustain power.

Gasoline turbo engines: Versatile and powerful at low and mid rpm, but limited at very high rpm. Turbo upgrades can improve performance.

Why modern F1 cars are so fast: They combine gasoline turbo engines with extreme rpm (up to 15,000), hybrid systems for extra torque, and advanced aerodynamics for maximum performance.

High-revving naturally aspirated engines: Shine at high rpm with linear power delivery, perfect for track use and thrilling high-speed driving.

I hope this article gave you more insight into how torque and horsepower affect the driving behavior of different engine types. Whether you prefer turbodiesels, gasoline turbo engines, or high-revving naturally aspirated engines, each offers unique performance and driving experiences. Ultimately, the choice depends on your personal preference and intended use.

[needless rules]

Hello,
It's great to see some math and science on this website, instead of members concerned that their wheels and calipers don't match. Thanks

[No one]

Torque is how much dough you have. Revs is how much you want to spend. Power is how much you can buy. Turbo is a loan. Chip tuning is pure marketing.

[Mason Hatcher]

Originally Posted by snoep

WHAT MAKES YOUR CAR FAST? THE DYNAMICS OF TORQUE AND HORSEPOWER

Are you the author?

[snoep]

Originally Posted by Mason Hatcher

Are you the author?

Yes, I am.

[Mason Hatcher]

Originally Posted by snoep

Yes, I am.

Very well done!

[snoep]

Following up on the start topic, where I discussed torque and power curves in relation to driving dynamics, I want to examine a specific case to provide more insight. What happens to the driving experience when power starts to decline? The Ford Focus ST 2.0 MK3 PH2 with its 2.0-liter EcoBoost engine and tuning serves as a great example to illustrate this.



The power and torque curves of a car reveal a lot about how the engine performs across different RPM ranges. With this Ford Focus ST, one thing stands out: the peak power of 285 hp at 5000 rpm drops to around 262 hp at 6500 rpm.



This loss of nearly 10% of power after the peak has a noticeable impact on the driving experience, particularly during hard acceleration and pulling through the higher RPM range. Let’s analyze what this means for driving dynamics and why it happens.

What Do the Power and Torque Curves Reveal?

1. Early Power Peak (Around 5000 RPM)
At 5000 rpm, the engine delivers its peak power of 285 hp. This is typical for engines equipped with a compact turbo, as the turbo is most efficient at this RPM range and delivers maximum airflow and performance.

2. Power Drop to 262 HP at 6500 RPM
After 5000 rpm, power begins to decline significantly. By 6500 rpm, just before redline, the power has dropped to 262 hp, a loss of 23 hp (roughly 10%). This means the engine becomes less powerful as you push further into the rev range, which makes acceleration above 5000 rpm feel less aggressive.

3. Torque Drops Before Power Does
The maximum torque of 526 Nm is achieved between 2500 and 4000 rpm, providing a strong and responsive experience in the midrange. However, torque starts to drop before 4500 rpm. Since power depends on both torque and RPM (Power = Torque x RPM / 7023), this decline in torque is the main driver of the falling power curve after 5000 rpm.

What Does This Mean for the Driving Experience?

Strong Midrange Performance (2500–4500 RPM):
In the midrange, the Focus ST feels lively and responsive. The high torque of 526 Nm delivers a strong "push in the back" during acceleration, making it ideal for overtaking and spirited driving on twisty roads. The engine feels smooth, powerful, and highly capable in this range, making the driving experience enjoyable and convincing.

Less Aggressive at High RPM (5000–6500 RPM):
Above 5000 rpm, the car’s character changes significantly. Power starts to drop noticeably, which makes acceleration feel less sharp and eager. Where sportier engines often maintain or even increase power output as they climb towards redline, this Focus ST feels like it "runs out of breath."

This has a clear impact on the driving experience. During hard acceleration—whether in a sprint or when pulling at higher speeds—the engine seems to lose some of its strength as you approach the redline. While the car is still plenty powerful, it feels less dynamic and exciting in this range, especially when compared to its strong midrange performance. For drivers who enjoy wringing out every bit of performance from an engine, this can be somewhat disappointing.

Why Does This Happen?

1. Limitations of the Compact Turbo:
The EcoBoost engine’s relatively small turbo is designed to build boost quickly at low and midrange RPM. This makes the car responsive and powerful in everyday driving scenarios. However, at higher RPM, the turbo reaches its airflow capacity and can no longer supply enough air to fully fill the cylinders. This results in declining torque, and consequently, falling power.

2. Engine Design:
The 2.0 EcoBoost engine is optimized for a wide torque band in the low and midrange RPMs, making it very suitable for daily driving. However, it’s not designed for high-revving performance like naturally aspirated sports engines, which typically gain more power as RPMs increase. This hardware limitation means that tuning can only partially address the issue.

3. Characteristics of the Tune:
Most tuning focuses on increasing torque and power in the low and midrange RPMs, where the engine spends most of its time. This means that the decline in power at higher RPM often remains unresolved or can even be exacerbated when the turbo is pushed closer to its limits.

Conclusion
The Ford Focus ST 2.0 MK3 PH2 delivers solid performance after tuning, with a peak power of 285 hp and 526 Nm of torque. In the midrange, the car stands out with strong, responsive acceleration, making it well-suited for everyday use and driving at lower RPM.

At higher RPM, however, the engine’s character noticeably shifts. Power drops significantly after 5000 rpm, falling to around 262 hp at 6500 rpm. This results in less aggressive and dynamic acceleration at the top of the rev range. For drivers who are used to wringing every bit of performance out of an engine, this decline can feel underwhelming and limits the car’s overall excitement at higher speeds.

To address this, upgrades such as a larger or hybrid turbo, or improvements to the intake and exhaust systems, would be necessary. Without these changes, the Focus ST remains a capable car with strong midrange performance, but it shows clear limitations in delivering sustained power at high RPM.

[Jaizero]

HP=TQ(ft/lbs)*RPM/5252

If you want to use ft/lbs instead of nm.

[Tejas1836]

HP is how fast you hit the wall, Torque is how far through the wall you go

[snoep]

Originally Posted by Tejas1836

HP is how fast you hit the wall, Torque is how far through the wall you go

The statement "HP is how fast you hit the wall, Torque is how far through the wall you go" is a popular way to explain the difference between horsepower (HP) and torque, but it's not entirely accurate from a technical standpoint. While it's catchy, it's not technically precise.

Let me clarify:

Horsepower (HP) is a measure of power, which is the rate at which work is done. It combines both the force (torque) and the speed (RPM) at which the engine operates. Essentially, horsepower determines how quickly a vehicle can perform work, such as accelerating.

Torque is a measure of the rotational force the engine can produce. It indicates how much force the engine can apply to turn the wheels. High torque is especially useful at low speeds, such as when starting from a stop or towing heavy loads.

Gear Ratios determine how the engine's power is transmitted to the wheels. A lower gear (with a higher ratio) increases the torque at the wheels, which is helpful for starting and climbing. Higher gears (with lower ratios) reduce torque but increase speed, making them more efficient for highway driving.

Improved Analogy

Horsepower (HP): Think of horsepower as determining how fast you can move a heavy box. More horsepower means you can move the box faster.
Torque: Torque determines how easily you can lift that heavy box. More torque means it takes less effort to get the box moving.
Gear Ratios: The gearbox acts like a lever. In a low gear (high ratio), you can lift the box more easily (more torque), but you move it slowly. In a high gear (low ratio), you can move the box faster, but it takes more effort to start.
This combination ensures that a vehicle can be both powerful and fast, depending on the driving conditions and the selected gear.

I hope this helps clarify the concepts!

[Tejas1836]

AI learning bot

[No one]

Horsepower is a unit of measurement. That is, if you are not a horse (face? ) the power you possess is not a horse one, but it can be measured in relation to a horse's.

Originally Posted by Tejas1836

HP is how fast you hit the wall

A fast blow is not necessarily powerful.

Originally Posted by Tejas1836

Torque is how far through the wall you go

Using inertia is cheating: it's not your pure force.

Here most of the tiles are broken with a blow (power) and the rest with a push (torque).

It's torque that gives you power, not vice versa.

Originally Posted by snoep

Horsepower (HP): Think of horsepower as determining how fast you can move a heavy box. More horsepower means you can move the box faster.

Mindpower is putting the box on wheels.

Originally Posted by snoep

Torque: Torque determines how easily you can lift that heavy box. More torque means it takes less effort to get the box moving.

Torque determines what a heavy box you can lift without making that easy.

[snoep]

Originally Posted by No one

It's torque that gives you power, not vice versa.

Not exactly. Torque and power are closely related, but neither inherently "gives" you the other—they’re two aspects of the same mechanical output. Power (horsepower) is a function of torque and RPM. The formula makes it clear:

In metric units:
Horsepower (hp) = (Torque (Nm) × RPM) / 7023

In imperial units:
Horsepower (hp) = (Torque (lb-ft) × RPM) / 5252

Torque without RPM results in zero horsepower, which means no mechanical work is being done—and the car won’t move at all. Both torque and RPM are necessary to generate power and actually get a vehicle moving. It’s the combination of torque and how it’s applied across the RPM range that determines performance.

[snoep]

Originally Posted by No one

It's torque that gives you power, not vice versa.

Not exactly. Torque and power are closely related, but neither inherently "gives" you the other—they’re two aspects of the same mechanical output. Power (horsepower) is a function of torque and RPM. The formula makes it clear:

In metric units:
Horsepower (hp) = (Torque (Nm) × RPM) / 7023

In imperial units:
Horsepower (hp) = (Torque (lb-ft) × RPM) / 5252

Torque without RPM results in zero horsepower, which means no mechanical work is being done—and the car won’t move at all. Both torque and RPM are necessary to generate power and actually get a vehicle moving. It’s the combination of torque and how it’s applied across the RPM range that determines performance.

[Tejas1836]

Originally Posted by snoep

Not exactly. Torque and power are closely related, but neither inherently "gives" you the other—they’re two aspects of the same mechanical output. Power (horsepower) is a function of torque and RPM. The formula makes it clear:

In metric units:
Horsepower (hp) = (Torque (Nm) × RPM) / 7023

In imperial units:
Horsepower (hp) = (Torque (lb-ft) × RPM) / 5252

Torque without RPM results in zero horsepower, which means no mechanical work is being done—and the car won’t move at all. Both torque and RPM are necessary to generate power and actually get a vehicle moving. It’s the combination of torque and how it’s applied across the RPM range that determines performance.

quillbot.com

[snoep]

Originally Posted by Tejas1836

quillbot.com

This is nonsense. If you have nothing substantive to say about the subject of the thread, please go talk your nonsense elsewhere.

[GuidoK]

Engine torque gets you nowhere. It's torque at the wheels.
And what is your gearbox/final drive?
Thats right, a giant torque converter.
So those conclusions regarding acceleration are highly subjective to the ratio's.
And if you have a CVT or a gearbox with lots of gears spaced properly: the higher horsepower car will win. As horsepower is a converted energy measurement of the amount of energy your engine puts out per segment of time (1HP=~0,75kW, 1W=1J/s).

[Bc2005]

Earlier in life I drove Hondas and Mazdas, which had fun high revving engines, but max torque and HP came in at a relatively high RPM. They were fun to drive with a manual transmission because you could keep the revs up, but felt slow with most automatic transmissions (paddle shifters were uncommon). I spent a lot of time near 5000 rpm.

BMW has been able to tune the engine/turbo/trans package in the M340i so that it begins to provide nearly max torque at 1200-1500 rpm. It makes it a great daily driver because even light throttle input will downshift the transmission, kick up turbo boost, and ensure you get the high torque you want. It always feels fast. I think it probably also contributes to its excellent gas mileage, because you never really need to “give it gas” to merge and keep up with traffic. YMMV