#smallengines #horsepower #torque #highpower #engineperformance
Have you ever wondered why small engines can produce high horsepower, but struggle to generate high torque? 🤔 It’s a common question among car enthusiasts and those interested in engine performance. In this article, we will delve into the intricacies of engine design and performance to understand why this phenomenon occurs.
## The Basics of Horsepower and Torque
Before we dive into the specifics of small engines, let’s first clarify the concepts of horsepower and torque:
– **Horsepower:** This is a measure of an engine’s power output and is calculated by multiplying torque by engine speed (rpm) and dividing that product by a constant. In simple terms, horsepower is the rate at which work is done.
– **Torque:** Torque, on the other hand, is the rotational force produced by the engine. It is essential for accelerating a vehicle and overcoming resistance. Torque is typically measured in pound-feet (lb-ft) or Newton-meters (Nm).
## Small Engines and High Horsepower
Small engines, like those found in the Honda S2000 or Ferraris, are known for their impressive horsepower figures despite their size. This is due to several factors:
1. **High Revving:** Small engines often have higher rev limits, allowing them to reach higher engine speeds. This results in increased horsepower output, as horsepower is directly proportional to engine speed.
2. **Efficient Cylinder Head Design:** The design of the cylinder head in small engines is optimized for high airflow, which improves combustion efficiency and power output.
3. **Advanced Engine Management Systems:** Modern small engines are equipped with sophisticated engine management systems that optimize performance and fuel delivery, leading to higher horsepower figures.
4. **Lightweight Components:** Small engines are constructed using lightweight materials, reducing overall engine weight and improving power-to-weight ratio.
## Challenges with High Torque
While small engines excel in producing high horsepower, they often struggle to generate high torque. This is primarily due to the following reasons:
1. **Displacement:** Torque is directly proportional to engine displacement. Small engines have limited displacement, which restricts their torque output compared to larger engines.
2. **Compression Ratio:** High compression ratios, which are common in high-horsepower small engines, can limit torque output. This is because high compression ratios can lead to knock and pre-ignition issues when trying to produce high torque.
3. **Exhaust Gas Velocity:** Small engines may face challenges in maintaining optimal exhaust gas velocity at low rpm levels, which can impact torque production.
4. **Lack of Low-End Torque:** Small engines are often tuned for high-end power, sacrificing low-end torque in the process. This can result in a lack of torque at lower rpm levels.
## Balancing Horsepower and Torque
Achieving a balance between high horsepower and torque in small engines is a delicate process that requires careful engineering and design considerations. Some techniques that can help improve torque output in small engines include:
– **Optimizing Intake and Exhaust Systems:** Enhancing airflow into and out of the engine can improve torque production across a wider rpm range.
– **Variable Valve Timing:** Implementing variable valve timing technology can optimize engine performance at different rpm levels, enhancing both horsepower and torque output.
– **Forced Induction:** Superchargers or turbochargers can be utilized to increase torque output in small engines by forcing more air into the cylinders.
– **Fuel Injection System:** Upgrading to a high-performance fuel injection system can enhance torque delivery by ensuring precise fuel delivery and combustion.
By carefully considering these factors and utilizing advanced engineering techniques, it is possible to improve the torque output of small engines without compromising on horsepower performance.
## In Conclusion
While small engines may struggle to produce high torque compared to larger engines, they excel in generating high horsepower due to their design and engineering advancements. By understanding the nuances of engine performance and implementing strategic modifications, it is possible to enhance torque output in small engines while maintaining impressive horsepower figures. Remember, the key lies in finding the right balance between horsepower and torque for optimal engine performance. 🚗💨
So, the next time you marvel at the high horsepower figures of a small engine, remember the intricate interplay between power and torque that goes into making it a high-performance marvel on the road!
In a word. Leverage.
High torque engines use longer throws on their crankshaft, which allows the pistons to exert more leverage on the crank as they fire.
High revving, short stroke engines such as those you mentioned have to keep everything more compact because at such high speeds everything is under a tremendous amount of stress, if you tried to make a high torque engine such as one out of a semi rev the same as a Ferrari, it would fly apart because the materials simply don’t have the strength to hold together.
So, because a short stroke engine can’t exert as much leverage on the crank, it cannot generate high torque.
The way I understand it is that imagine hitting a standard hammer against a wall. You can hit it either rapidly or hard. Any attempts to hit the wall rapidly and hard at the same time will require an immense amount of strength and energy. You’ll also get fatigued very quickly. The same principle applies to pistons inside the engine.
torque is how powerful something is in one revolution of the engine. hp is how powerful it is over time. so, a small engine spins really fast to make that hp.
you can get small engines to rev really high and make a ton of hp, but they feel like a limp noodle until you reach the powerband.
motorcycles hit this point hard. my 650cc bike is slower than a 600cc supersport. the supersport revs almost twice as high and makes about the same torque, just way up in the revs. at those same revs it makes about 40% more hp though.
Torque and horsepower are not two independent properties of an engine, they’re tied together via the RPM by a formula:
T = P * 9549 / r
Where T is torque in N*m, P is power in kW, and r is rotational speed in RPM. (for power in HP and torque in lb*ft the coefficient is 5252)
So if you have a 10 kW engine and connect it to a gearbox which outputs, say, 950 RPM, you will get around 100 N*m of torque regardless of the engine “size”.
Have you ever unscrewed a screw?
When you first have to un-tighten the screw out of the wood, have you ever noticed how hard it is to do that by the metal shaft of the screwdriver? It’s so much easier to unscrew by the handle. But once it’s loose, you may have noticed that it just takes forever to *keep* using the handle, so you use the metal shaft instead, and then it turns like lightning.
That’s what’s going on in cars. Small engines are like the metal shaft of the screwdriver. They’re crazy fast, but only for stuff that isn’t very demanding. Bigger engines are more like the handle. They’re great if you need some real work done, but they take forever to get anything done if there isn’t much work for them to do.
The reason ultimately boils down to the fact that, perhaps unintuitively, when you push on something, it actually *pushes back*. When a car’s gear tries to twist the axel, the axel tries to twist back. It doesn’t wanna be twisted. So it starts a little war between the gear and the axel, where both of them are trying their hardest to twist back against the forces causing them to fight each other.
Each of them brings their own set of allies to the fight. The gear is bringing the engine and the explosions in its pistons. The axel is bringing the weight of your car and the friction of the road beneath the wheels. If the gear and its allies are stronger, the gear wins out, and the car is forced to move.
But suppose the axel wins because the car is just too heavy, so the gear’s allies come to a stalemate. How should the gear proceed in order to get moving again?
Well, bringing more firepower to the fight usually helps. One way is to bring a bigger, badder gear. That can tip the scales in the gear’s favor and allow things to move again.
But large armies take a lot of time to move and coordinate. If your army is very wide, then the troops at the edge of your army will need to march a lot farther in order to turn around than the troops in the middle. If you want to have the ability to turn around quickly, you need a smaller army.
So if the axel isn’t putting up much of a fight and you just want to steamroll its allies and get the war over with, you’d be better served with a smaller, more nimble gear.
Hope that helps.
Car engine stats are as much marketingspeak as physics…..
Eg, actual practical torque at the wheels is a matter of the transmission as much as the engine…..
You can take a really high winding engine, hook it to a beast of a transmission, and get gobsmacking amounts of torque on the ground (see the M1 tank and it’s turboshaft engine – the transmission is a few times larger than the engine, and turns 1500 shaft HP at a-million-something-RPM into 2500ftlbs torque at the tracks & the ability to make 70 tons go remarkably fast)
Although you can measure the horsepower of an engine, when you see horsepower stats for vehicles they are never measuring that. Rather, they’re measuring how much force can be used to spin the wheels when the car is in its highest gear at the engine’s optimal RPM. Because that’s how horsepower is measured in the real world, it makes more sense to think of torque as a measure of the raw power of the engine and horsepower as a measure of how efficiently the transmission can convert that power into work.
High performance cars tend to weigh as little as possible because weight is the biggest cost constraint in attaining good acceleration, top speed, and handling. IE, if Car A weights twice as much as Car B, it will cost a lot more to make Car A perform the same as Car B on a racetrack. So if you have a $150k budget for your new Ferrari, the way you make that Ferrari go as fast as possible is to make it as light as possible.
The two biggest sources of weight in a car are the engine and transmission. The more torque an engine produces, the heavier both it and its transmission have to be to survive the forces being applied to them. But like I said, weight is expensive and the goal of high performance cars is to weigh as little as possible. This means that you want the lightest possible engine and transmission for the performance that you can obtain.
The way that sports cars do this is by having *relatively* low powered engines (at least compared to heavier cars like trucks) that produce power through the use of a complex transmission that has a large number of gears. Adding more gears doesn’t add any more weight, but it does allow you to have a much higher gear ratio in the highest gear. That higher gear ratio allows you to very efficiently convert the engine’s torque into work when the car is already travelling at high speeds, producing more horsepower than the engine otherwise would with fewer gears.
This isn’t to say that a Ferrari doesn’t have a powerful engine – a typical Ferrari has an engine that produces about as much torque as the engine in an F-150. But when you start to get into more mid-range sports cars, like the Porsche Boxster, you also start to get engines that are producing 2/3 as much torque as a typical truck.
Interesting fact. Torque and horsepower always intersect at 5250 RPM:
https://poweretty.com/blog/why-do-horsepower-and-torque-always-cross-at-5250
What people miss is that what you care about is wheel torque, not engine torque.
Say you have an engine that puts out 200 ft lbs at 4000 rpm and a smaller engine that puts out 150 ft lbs at 8000 rpm.
Take the 8000 rpm one, feed it into a 2:1 gear reduction, and it’s putting out 300 ft lbs at 4000 rpm.
This is why sportbike engines rev so high. It allows you to run lower gearing and that gives more torque at the back wheel.
It’s not that smaller engines can’t be built to feel torquey, they just aren’t in these applications. They’re used in a car like the S2000 because they’re lightweight, but to make higher power figures they’re designed to have a high rpm powerband. Looking at the numbers, the S2000 actually makes a respectable amount of torque for a 2.0L engine. The reason it feels lacking in torque is because that torque is found at 7000+ rpm, and the engine won’t make as much torque outside of that powerband-above or below. A basic Civic has a 2.0 with similar torque at ~4000rpm, but it will lose torque as you rev past that. You can expand this powerband with VVT and fancy intakes but it is still limited by several different factors in engine design.
In short, an engine can be designed for torque at high rpm, or at low rpm, but doing both in one engine is difficult.
An ideal internal internal combustion engine has constant torque. That torque value is proportional to displacement, which makes sense if you think about it from first principles.
Torque is the product of a force applied to a lever arm.
The force is proportional to the area of the piston.
The lever arm length is proportional to the stroke of the piston.
Torque ∝ Area x Stroke ∝ Displacement
Since power is proportional to torque x angular velocity, to make more power from a given displacement, you need to rev higher.
In the real world, there are fluid dynamics effects that cause the torque curve to NOT be a flat line, and there are material property limitations that enforce a RPM limit. Race engines are engineered to rev to the moon, and to have useful torque up in that rev range.
Horsepower is a mathematical result of torque and rpm. Small engines have less mass and so can generally spin faster without damaging themselves or coming apart. The equation is (torque × rpm) ÷ 5252. If you look at a graph of horsepower and torque over the rpm range, the values for horsepower and torque cross at 5252 rpm
Not true. Small turbocharged engines can make big torque. Only small naturally aspirated engines don’t. Torque is generally very closely related to engine size.
It’s probably worth understanding how hp is calculated. It’s calculated from torque and revs. So you can get more hp from more Reva even with the same torque.
Small engines can make high torque, but only with leverage and a low revolution speed of the shaft you are measuring torque on. They can’t produce high revs *and* high torque.
In the simplest terms, horsepower is revs times torque.
A low torque engine can only make high horsepower by spinning really, really fast. The cars you listed have high rev limits, meaning they’ve got lots of light and strong parts. These parts make the engines expensive but powerful.
A high torque engine is usually much heavier and slower and can’t spin as much.
Torque is twisting force. In order to have a lot of twisting force you need a big heavy engine whose crankshaft and piston stroke can provide it due to higher leverage, but also the heavy rotational mass of the engine contributes to its power. Horsepower is just the rate at which work is produced. It’s not very intuitive and hard to grasp for most people but on a basic level a higher work output can “make up” for lack of torque but it’s not without downsides. You can make a small engine rev fast and have high horsepower because its moving components are light and its piston stroke short, but the common saying that “there’s no replacement for displacement” holds true.
So basically, if you have a diesel pickup truck with 200HP and a Honda hatchback with 200HP, both can tow a trailer, it’s not like the Honda can’t get moving at all, but the pickup will leisurely pull the trailer along with maybe a few hundred rpm more on the tachometer while the Honda will be revving very high at all times just to get moving. That’s not very practical for many reasons.
Just a comment on the torque of Ferrari engines. For example, the engine in the 812 Superfast produces 800 PS (588 kW; 789 hp) at 8,500 rpm and 718 Nm (530 lbft) of torque at 7,000 rpm, so it’s not exactly lacking on either front.
A crankshaft needs to make two revolutions for all cylinders to fire. A four cylinder engine will fire once every 180 degrees. An eight cylinder will fire every 90 degrees. There is more force exerted onto the crankshaft.
As others have said, the distance the piston travels (stroke) does play a part as well. A longer stroke means the piston pushes on the crankshaft longer. However, there is only a very tiny rotational period where force is applied by the piston. What can make a substantial difference is the rod/stroke ratio. Changing the rod length does not change the stroke, but it does change when the piston accelerates and decelerates the most.
I highly recommend the YouTube channel Driving 4 Answers, he is marvelous at explaining this.
Small engines can generate high torque you just have to attach them to huge flywheels. The old John Deer B had a single piston 4 cycle engine with 17 horsepower but a huge flywheel that gave it tons of torque.
Horsepower is a “fake” metric determined by force/rpm. If you spin something faster it can do more work with less force, but you need the speed to get that power. If you are able to easily reduce that speed you lose that power.
In short the force of torque never changes but the amount of work you can do with that torque can be manipulated to give you high horsepower numbers, which even though I described it as “fake” is actually able to be implemented with mechanical advantage of gearing (leverage) but it still doesn’t have the ass of a larger engine because those use brute force to get the same number at a lower speed. If you increase the speed of a larger engine you would be able to get even more absurd amounts of horsepower but that would also require compromises in different aspects of the design in terms of the material cost, strength to weight etc.
Here is the simplest explanation that almost every single post so far is missing and way over complicating.
Torque is basically a measure of how big the explosion inside the cylinders are. What determines how big the explosion inside the cylinders are, is how much air and fuel each cylinder can suck in during one engine cycle. What determines that, is the engine displacement, or how “big” the cylinders are.
Big engines, like truck V8s, can suck in A LOT of air and fuel each cycle. That means the explosions are big, and a lot of torque is generated.
Cars like the Honda S2000 and most Ferraris have small engines, with small displacements. That means each individual explosion is small, and the resulting torque is low.
The trick is, you can spin the small engine really fast. So you get a lot of really small explosions, that can ultimately generate a lot of power. Small engines are preferred for many racing cars because of their lightweight and compact size.
Horsepower isn’t a “real” force, it’s a measurement of torque over time: Torque x RPM/5252. Torque is the real, measurable force.
Think of an engine as an air pump. The pump has an internal capacity that you can fill every revolution. A 2L pump has a lower capacity than a 3L pump, so for each revolution, it’s going to pump less air. That per-revolution amount is torque, it’s the amount of work the engine can do in one revolution. If you increased the speed of of the pump, it multiplies the amount of work that can be done in a specific period of time, so even a low capacity pump can do a lot of work if you rev it high. Revving high tends to be easier with smaller pumps since all the moving parts are lighter, which is why you don’t usually see large, high revving motors. There are other things you can do to increase the amount of work the pump can do in one revolution, like forced induction, but that’s the basics.
High revving motors actually don’t have low torque for their size, they’re just lower sized so they can rev higher, basically. For some applications, like a racing car, that’s better than a larger, lower revving motor, generally speaking, so that’s why you see them in an S2000 or Ferrari.
Horse power is calculated from the number revolutions per time and torque (i.e force exerted over a length) of an engine. This means you can have two engines with identical HP, but one delivers little torque with high rev and the other delivers massive torque with very slow rev. We use HP for cars regardless, because the revs are standardized, so you can always assume that it just has higher torque than previous generations of cars with less HP. When you switch vehicles/machines, you should obviously remind yourself of this, so you won’t expect a very fast tractor that has more HP than a sports car, and vice versa don’t expect a sports car to be able to tow a truck. (of course there are exceptions everywhere, the point is that HP alone doesn’t say much about the motor and the type of vehicle that has the motor with the HP in question can only give a good guess of what revs and torques to expect).
His videos are pretty awesome but I think he covers it in this video.
For the same reason, when you have a really stuck on bolt, you either grab a longer wrench or use a hickey bar.
Torque is the measure of force about an axis. A simple example of what this means is as follows:
Imagine you have to loosen a stubborn, rusted lug nut on the wheel of your car. Suppose you have the options of using a 6-inch wrench or a 24-inch wrench to loosen the bolt. Which one will you choose and why?
Knowing the bolt is rusted and stubborn, you’ll choose the longer wrench. You apply that wrench to the bolt and apply force by pressing down on the handle of the wrench. That’s what torque is – the downward force on the wrench about the axis (the bolt) you are creating/applying torque to that bolt. When you apply enough force onto that bolt, it will break free. The longer wrench makes it easier to apply more force without any additional effort. The formula for torque is distance multiplied by the force. The US measures torque in units such as in.lbf or ft.lbf, whereas the metric system will use something such as N.m (Newton meters). In any case, these units indicate the length of the thing which is applying torque and the applied force.
Suppose you have to apply around 250 ft.lbf of force to overcome that rusted bolt. With a 6 inch wrench, the formula becomes 250 ft.lbf = 0.5 ft (this is converting 6 inches to feet) * X lbf.
Divide both sides by 0.5 ft to determine X.
250 ft.lbf / 0.5 ft = 500 lbf. That means with a 6 inch wrench, you would need to hold the handle by the end and apply 500 pounds of force to get that bolt to break free. Most people will not be able to apply that amount of force and it’s impractical and dangerous to do so with a 6 inch wrench even if you could.
Let’s solve for the 24 inch wrench instead.
250 ft.lbf = 2 ft (this is converting 24 inches to feet) * X lbf.
250 ft.lbf / 2 ft = 125 lbf. That means with the 24 inch wrench, you would only need to hold the handle by the end and apply 125 lbf of force to get the bolt to break free. Most people could do this by grabbing the handle and applying body weight to it. Finishing this example, a 6 inch wrench simply cannot generate the same amount of torque as a 24 inch wrench – the physics do not work. However, you would be able to spin that 6 inch wrench much faster than the 24 inch wrench. So once the bolt was free, if you had a lot of threads, you could switch to a smaller wrench and spin that bolt off much faster.
Think of the smaller engines like the smaller wrench and bigger engines like the bigger wrench. Smaller engines will be able to spin things generally faster, but they won’t be able to spin with as much force as a big engine. Likewise, the big engine is unlikely to spin faster than a small engine, but it will do so with more force.
Torque is the product of the cylinder pressure * the cylinder surface area * the amount of offset in the crankshaft (in whatever units you care to use/convert to).
Horsepower is torque * RPM. That’s why the curves always [cross at about 5252](https://www.enginelabs.com/engine-tech/engine/tech-talk-why-does-a-dyno-graph-always-cross-at-5252-rpm/) in common US units.
Small engines have small cylinders and small crankshafts, so they have small torque. Those lighter components allow them to spin very fast, so they make up in RPM what they lack in torque.
horsepower = torque * speed.
if a small engine makes high horsepower, it does this at high speed, hence the relatively low torque. The exceptions (think VW 1.4 TFSI), use high boost at low speed and come with high torque.
Torque is produced by the force applied by a piston to the crankshaft. The larger the diameter of a piston (for a given cylinder pressure) the higher the force applied to the crank because the surface area of the piston is greater. Also, the higher the diameter of the piston, the more fuel and air you can squeeze into the combustion chamber, increasing the energy applied to the piston.
A small engine with small pistons simply cannot produce as much rotational force as one with larger pistons.
Power is a product of several factors, one of which is how fast the engine spins (how many combustion events happen in a given period of time). A small engine can still spin fast (usually faster than a larger one), and can therefore be designed to reach decent power levels.