The first two digits of the type number are the engine displacement in cubic inches: in your case, 12. My 3.5 horsepower Victa has a 9 cubic inch (148 cc)engine with the pulsajet carburetor (model 92808). However I also have a 9 cubic inch with a vacujet carburetor (model 92508 - the third digit tells you which carburetor is fitted) on a Rover, and it had less than 3 hp so B&S simply did not state the power output. (In their overhaul manual they say they had decided to reduce the engine's maximum speed when fitted to rotary mowers, 'for safety reasons.' The pulsajet engines produce maximum hp at 3,600 rpm, compared with less than 3,000 rpm on the vacujet versions). Perhaps they had similar multiple versions of 12 cubic inch Quantums, and if so this might be the reason there was no horsepower label on yours - it would make commercial sense for them to only put a label on the highest-output version. I'm just guessing of course. I do know that I like my 3.5 hp Victa's engine better than my less-than-3 hp Rover's.
