In case you haven't looked at it yet, I've posted a question on some Hispano-Suisa data plates I have in my collection which you should still be able to see on the first page of this section of the forum. So far I have no replies to my question there, but you can see that as of around 1916 to 1917 when Hissos to which these were attached were made the horsepower ratings seemed to be in the 150 - 180 - 200 range so with the speed of engine development that was going on at that time, I believe that it would be reasonable to believe they were up to 300 HP by 1918. Dan San really knows his stuff and I would trust the numbers in his response to you.
By the way, I'm not sure of your intention in your last post, but it comes across as somewhat negative which is a puzzle since Dan San seems to have given you a definitive answer to your question.
Regards,
Jim