what bob said. What he didnt mention is how you get hp from how much torque you have. If you could somehow measure the torque on your engine you would use this formula to get your horsepower number. example: If you had a engine that produced 0.88ft lbs of torque at 15,000rpms. You would take those two numbers and multiply them together and then divide that by 5252. this will give you your horsepower number.

.88 times 15000/5252=2.5hp

If you are curious this will work for any type of engine