It's tough to compare engines based on stats alone. Sure, your Camaro's V-8 might have more horsepower than your buddy's old M5, but that's not the entire story. If you want to get a true apples-to-apples comparison between engines, you have to calculate BMEP.
Brake Mean Effective Pressure (BMEP) is essentially the average pressure forcing the pistons inside your engine down that provides the measured torque output. There's a fair bit of math behind it, but the equation itself is pretty easy to grasp. Road & Track contributor Jason Fenske explains it well in his latest YouTube video above.
In a way, BMEP is a fancier, more accurate way to calculate torque per liter. As Fenske points out later in the video, a naturally aspirated engine's BMEP number can be fairly compared against others, as long as they run on the same sort of fuel. Perhaps the most surprising result is Ford's 5.0-liter V-8, found in the current Mustang GT. It has a higher BMEP than even Ferrari's 6.2-liter V-12 in the 812 Superfast.
Of course, stuff gets complicated once you throw turbocharged engines into the mix. Since more air is being forced into the engine, the BMEP number is essentially multiplied. Fenske provides a few examples of how you can still compare them by factoring out the turbo, though, which is neat.
＜引用終わり＞
BMEP
正味平均有効圧（Brake Mean Effective Pressure）
実際にエンジンから得られる仕事（図示仕事から補機類、ピストンの運動抵抗などを差し引いて計算される）を行程容積で割ったものです。エンジンの燃焼効率を判断する目安の1つとなります。
