If I understand the question, you are refering to the pressure developed, in the cylinder, from the fuel charge burning. That is as varied as the engine, the rpm, the degree of tune, fuel, load etc, etc, etc. That pressure translates to horse power/torque. I didn't see that the linked article addressed this question. I would like to see some definitive figures.
Seems to me that if one had an engine with two plugs per cylinder, a compression gauge could be installed in place of one of the plugs and the engine run at various speeds to, at least, get some idea.
