Definition of "horses"

I got four hundred horses tucked under the hood.

1979, Al Greenwood, Lou Gramm, “Rev on the Red Line”, in Head Games

This is a diagnostic test of your engine. You're supposed to have an output of a hundred and sixty-eight horses at sixty-two hundred R.P.M.s. You're nowhere near that.

1994, Blood (The X-Files), (Please provide the book title or journal name)