The cylinders are especially large, but the displacement is still only 2ℓ. I think the unusually high horsepower for a 2ℓ engine is not just because of high compression but also because ⓐ they normally run it at especially high revs, like your motorcycles; ⓑ they run it on a two-stroke cycle at low speeds, up to 3krpm; and ⓒ they optimized it to run on alcohols, which as you know have lower energy density but are better at keeping the engine cool.