How to Convert Horsepower to CC
Ever wondered what those HP and CC numbers actually mean when looking at vehicle specs? While horsepower and engine displacement are fundamentally different metrics, there are some simple calculations that make it possible to convert between the two. This comprehensive guide will teach you everything you need to know about measuring engine size and power.
Introduction
When shopping for a new car, truck, motorcycle, or other engine-powered machine, you’ll inevitably encounter technical specifications like “250 horsepower” or “3.5 liter V6”. But what do those numbers really mean in tangible terms, and is there a way to translate one into the other? As it turns out, there are straightforward mathematical formulas that make converting horsepower to CC (and vice versa) a breeze.
Understanding the relationship between an engine’s horsepower and displacement can offer valuable insights into its real-world performance and character. While horsepower measures power output, displacement reveals the physical size and potential torque. By learning how to make conversions between the two, you’ll be better equipped to evaluate and compare different engine configurations.
This in-depth guide will provide everything you need to know to:
- Understand what horsepower and displacement actually measure
- Use simple formulas to convert horsepower to CC
- Apply these calculations to gas, diesel, and electric motors
- Compare engines of different sizes and outputs
- Estimate fuel efficiency based on engine specs
- And much more!
So if you want to speak the language of engine specs like a pro, read on.
What is Horsepower?
First things first – what exactly does horsepower measure?
Horsepower (HP) is a unit that calculates an engine’s power output. Specifically, one horsepower equals the power needed to lift 75 kilograms a distance of one meter in one second.
Some key facts about horsepower:
- Abbreviated as HP or ps
- Based on mathematical calculations involving torque and engine speeds
- Measures how much actual work an engine can perform per unit of time
- Directly related to acceleration and towing capacity
- Not the same as torque, which determines the pulling power
Naturally aspirated engines typically generate anywhere from around 100 to over 700 horsepower depending on size and configuration. Forced induction from turbochargers or superchargers can boost power substantially beyond that.
When evaluating horsepower figures, more isn’t necessarily better. The power needs to be appropriate for the vehicle and application. Lower horsepower with ample torque often provides the best real-world drivability.
What is Engine Displacement?
While horsepower tells us how much work an engine does, displacement reveals its actual physical size.
Displacement is the total volume of air and fuel that an engine can draw into its cylinders. It is measured in liters (L) or cubic centimeters (cc).
Some key notes on displacement:
- Also called engine capacity or swept volume
- Calculated based on the cylinder bore x stroke x number of cylinders
- Directly corresponds to torque output
- Generally ranges from 1L to 6L for passenger vehicles
- Higher displacement typically delivers more low-end power
Larger displacement engines are capable of generating more torque, but they also consume more fuel. A smaller engine optimized for efficiency can often produce equal or better horsepower through technologies like turbocharging.
The Relationship Between Displacement and Horsepower
So how exactly are these two metrics related?
While horsepower describes power output, displacement defines an engine’s physical size and potential. Generally speaking, a larger displacement engine is capable of generating more maximum horsepower. However, other factors like the compression ratio, valve timing, and airflow also impact power.
The most useful measure of engine performance is brake horsepower per liter. This quantifies how much power an engine derives from each CC of displacement. Naturally, aspirated engines typically achieve 70-100 hp per liter or less. Forced induction and high-performance engines can reach over 200 hp per liter.
By comparing this ratio across different engines, you can better evaluate power delivery and efficiency.
Converting Displacement to Horsepower
Now that we understand the fundamentals behind these specifications, how do we actually convert between them?
Calculating Displacement from Horsepower
The most straightforward way to derive engine displacement from horsepower is to divide the rated horsepower by a standard power density factor for a given engine type.
Gasoline engines:
- Naturally Aspirated: 70 hp/liter
- Forced Induction: 110 hp/liter
Diesel engines:
- Naturally Aspirated: 40 hp/liter
- Forced Induction: 60 hp/liter
Electric motors: 250 hp/liter
Formula:
Displacement (L) = Rated HP / Power Density Factor
Examples:
- 350 HP NA Gas Engine: 350 / 70 = 5 L
- 450 HP Turbo Diesel: 450 / 60 = 7.5 L
- 600 HP Electric Motor: 600 / 250 = 2.4 L
This method provides a good quick estimate. For added precision, you can use actual measured power density for a specific engine model rather than the average factor.
Converting Horsepower to CC
To determine engine size in CC from horsepower:
- Convert rated HP to liters using the appropriate formula above
- Multiply liters by 1000 to convert to CC
Examples:
- 200 HP Naturally Aspirated Gas Engine
- 200 / 70 = 2.86 L
- 2.86 x 1000 = 2860 cc
- 320 HP Twin-Turbo Diesel
- 320 / 60 = 5.33 L
- 5.33 x 1000 = 5330 cc
So in summary, for gasoline engines:
- NA: HP / 70 = Liters
- Turbo/Supercharged: HP / 110 = Liters
Then Liters x 1000 = CC
This provides a simple way to get a quick approximate conversion between HP and CC in just a few steps. The actual relationship varies across specific engine designs based on the power density.
Factors that Determine Maximum Horsepower
While displacement puts a cap on potential horsepower, many other factors influence how much power an engine actually produces. These include:
- Compression ratio – Higher ratios increase power, typically from 8:1 to 13:1.
- Forced induction – Turbochargers and superchargers substantially boost horsepower.
- Valvetrain – More valves, aggressive cams, and variable timing add power up top.
- Fuel type – Higher octane gasoline allows more advance, boosting output.
- Air intake – Upgraded intake and free-flowing filters optimize airflow.
- Exhaust system – Minimizing restrictions through the exhaust frees up power.
- Engine management – Custom tunes via chipping extract maximum performance.
- Rotating assembly – Lightweight/forged components reduce parasitic losses.
- Fuel delivery – Larger injectors and multi-point injection increase flow.
- Materials – Forged components and racing alloys handle more stress and heat.
While these factors can all help an engine overachieve relative to its size, there are still physical limits imposed by displacement. But two engines of the same displacement can differ wildly in actual horsepower depending on the design.
Estimating Fuel Efficiency from Displacement and Horsepower
Another useful application of conversions between displacement and horsepower is estimating fuel efficiency.
As a general guideline:
- Smaller displacement engines tend to be more efficient
- Turbocharged small engines provide the best combination of power and efficiency
- 50-70 hp/liter is ideal for the best mileage
For example, a 1.5L turbocharged engine producing 110 hp equates to 73 hp/liter – right in that sweet spot.
While not universally true, higher horsepower engines typically have greater fuel consumption across engine types. Performance exhaust and intakes exacerbate this.
However, technologies like cylinder deactivation which shuts down cylinders during light load driving, can somewhat decouple size from efficiency.
In the end, published fuel economy ratings or actual testing remain the best ways to determine mpg. But using displacement and horsepower specs allows ballpark estimates of efficiency.
Gasoline vs Diesel Engines
The formulas provided above apply specifically to gasoline and diesel engines. But there are some important differences between these engine types to consider as well.
Gasoline engines rely solely on the spark plug for ignition. Diesel engines instead use compression to generate heat and ignite the fuel-air mixture.
Some key contrasts:
Gasoline
- Typically produce peak power at higher rpm
- A narrower power band focused higher in the rev range
- Require higher octane fuel to prevent pre-ignition
Diesel
- Max torque achieved at lower rpm
- The broader, flatter torque curve
- Compression ratios around 18:1 vs 8-11:1 for gas
- Greater low-end pulling power
- Higher thermal efficiency
As a result, diesel engines can achieve greater displacement in smaller overall package sizes. 1.5L-3L displacements are common for diesel passenger cars versus 1.5L-5L for gas.
Diesels also generate higher torque relative to horsepower compared to gasoline engines. However, modern turbo-diesels are closing this gap with equivalent or greater horsepower per liter.
Electric Motors
Electric cars add another wrinkle to the conversion process. Their power and efficiency differ substantially from internal combustion engines.
Some key attributes of electric motors:
- Generate full torque from 0 rpm
- Typically 90-95% peak efficiency
- Specific power over 1 hp/lb, up to 2.5 hp/lb
- Liquid cooling is essential
- Maintenance needs are minimal
- No transmission required
Tesla’s Model S P100D for example produces 778 hp, enabling 0-60 mph in just 2.5 seconds. Yet its motor displaces only 450 cc.
This equates to over 1700 hp/L – several times greater than the most powerful petrol engines.
The calculation assumes 95% efficiency and a power density of 1.75 hp/lb. Unique aspects of electric motors allow extreme power from very compact, lightweight packages.
Compare Specific Engine Examples
Let’s examine some real-world applications to see how these calculations apply across different engine configurations:
Toyota Prius 1.8L Inline 4 121 HP 67 hp/L 1800cc
This engine is optimized for efficiency over power. Low specific output but excellent MPG.
Ford Mustang 5.0L V8
460 HP 92 hp/L 5000cc
Iconic large V8 provides abundant power but gulps fuel. Respectable specific output for a naturally aspirated engine.
Chevy Volt Electric Drive 149 HP 298 hp/L 62cc
Electric motors achieve phenomenal specific power from very compact, lightweight packages. Minimal servicing needs too.
VW Golf GTI 2.0L Turbo Inline 4 228 HP 114 hp/L 2000cc
Small four-cylinder boosted by a turbo for potent performance combined with good fuel economy.
Dodge Ram Cummins Turbo Diesel 6.7L Inline 6 400 HP 60 hp/L 6700cc
Diesels like this Cummins can generate huge twists while delivering great efficiency and longevity.
Porsche 911 Turbo 3.8L Flat 6 545 HP 143 hp/L 3800cc
Advanced twin-turbo flat-six makes use of every CC while providing supercar performance.
Key Takeaways
To summarize the key lessons on converting displacement and horsepower:
- Displacement (CC) determines the maximum potential power
- Horsepower measures the actual power output
- Higher specific power (hp/L) indicates an efficient engine
- Simple formulas allow quick conversion between CC and HP
- Many factors beyond size affect horsepower
- Diesels optimize torque while gas focuses on peak power
- Electric motors achieve an incredible power density
Understanding the relationship between these fundamental engine specifications provides invaluable insight into real-world behavior and performance. By mastering these translation skills, you’ll be able to make informed comparisons and selections.
Whether you’re shopping for a new car or just want to boost mechanical know-how, learning to convert horsepower to CC (and vice versa) helps unlock the mysteries of engine specs. You’ll become fluent in discussing both engine size and power across any application.
Conclusion
This comprehensive guide examined every aspect of converting horsepower to engine displacement, and vice versa. We looked under the hood to understand what these fundamental specifications actually measure. Formulas and examples were provided to perform simple translations between the two.
Additional factors impacting horsepower generation were explored, highlighting why equally sized engines can produce vastly different power. And we compared the characteristics of gasoline, diesel, and electric configurations.
By developing fluency in the language of engine specs, you can evaluate the performance of any engine, from mighty diesel truck to electric supercar. You’ll be able to calculate displacement from horsepower or vice versa to compare specs. Understanding these fundamentals is crucial for making informed purchases and enhancing automotive knowledge.
So next time you encounter some engine specifications, use this guide as a reference to effortlessly convert between horsepower and CC. Knowing these translation skills will unlock new insight into how engines work and perform. You’ll be able to speak the language of HP and CC like an expert mechanic.
