We've been asked many times if you can calculate horsepower knowing only the displacement of an engine or if you can transfer horsepower to cc. The answer is no, you can't. Every engine model is unique in terms of horsepower-to-cc ratio and this figure is quite important.
Today, we'll have a quick look at what the horsepower-to-cc ratio is and why you can't calculate it properly knowing just one of these figures. We'll also tell you which factor is more important when you buy a vehicle.
Why can't you calculate cc knowing only horsepower?
You can't do that because you don't know how much power each cubic centimeter of this certain engine produces. For example, for some cars, it may be about 0.1 horsepower from 1 cubic centimeter while some other vehicles may only produce about 0.05 horsepower from 1 cc.
So, if you know only horsepower, you can't calculate cc whatever mathematic formula you would use for this. Even if you know the torque, you can only imagine what the displacement of this engine is.
The same is true for knowing the cc of the engine. By knowing only the displacement, you can't calculate horsepower or any other important specs. Because every manufacturer ensures that the engine produces a certain amount of power and torque from every liter of displacement and this figure is unique for every engine model.
Though, this question is wise because it drives you to another important understanding of engine performance.
Horsepower-to-cc ratio
When you know the displacement of the engine and also know its power, you can easily calculate the so-called horsepower-to-cc ratio. This ratio will show how much power each cubic centimeter produces in this certain engine.
For getting this ratio, you should divide horsepower by displacement in cubic centimeters. For example, your engine offers 200 horsepower and it's a 2000 cc engine. It means that every cubic centimeter produces 0.1 horsepower (200 hp divided by 2000 cc equals 0.1 hp/cc).
But a more practical and easy-to-understand method is counting horsepower from 1 liter of the engine. For this, the power in hp should be divided by the engine displacement in liters. For example, your 2-liter engine with 200 horsepower will produce 100 hp/l (200 horsepower divided by 2 liters equals 100 hp/l).
This ratio shows how well the engine performs. We mean that a 6-liter engine with 200 horsepower and a 2-liter unit with the same power will show absolutely different performance. The engine with a smaller displacement will show better performance because every liter of its displacement produces much more horsepower.
How should you use the hp-to-cc ratio?
It doesn't exactly mean that the engine with the highest possible hp-to-cc ratio is the most efficient. In most cases, this will mean that the engine is turbocharged, tuned, and works at the top of its possible performance. It means that this engine will have a much worse life expectancy.
The average hp-to-cc ratio is 0.1 hp from 1 cc or 100 hp from 1 liter of displacement. But manufacturers keep introducing new technologies that improve this specification and make engines smaller but more powerful.
This helps them ensure that the engines will consume less gas and emit less harmful gases into the atmosphere.
But, on the other hand, such engines live a shorter life. And you may remember that those old 6-liter trucks could easily go 400,000 miles while today's turbocharged trucks barely manage to get to 200,000 miles.
About the authors
The CarAraC research team is composed of seasoned auto mechanics and automotive industry professionals, including individuals with advanced degrees and certifications in their field. Our team members boast prestigious credentials, reflecting their extensive knowledge and skills. These qualifications include: IMI: Institute of the Motor Industry, ASE-Certified Master Automobile Technicians; Coventry University, Graduate of MA in Automotive Journalism; Politecnico di Torino, Italy, MS Automotive Engineering; Ss. Cyril and Methodius University in Skopje, Mechanical University in Skopje; TOC Automotive College; DHA Suffa University, Department of Mechanical Engineering
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