There's no exact cc-to-hp formula because horsepower depends on far more than displacement — tuning, turbocharging and engine design all matter. A common rough guide is one horsepower per 15 cc for naturally-aspirated engines.
For the engine
Keep it running.
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Frequently asked questions
Can you convert cc to hp exactly?
No — it's only an estimate. Two engines of the same cc can make very different power depending on design and boost.
What ratio does this use?
A common rule of thumb of about 15 cc per horsepower for naturally-aspirated engines.