If your current motor is lugging (blade slows down) as you cut, then you may need a more powerful motor. A 1/3 horse motor on an 18" saw sounds anemic to me. Lugging an AC motor is not a good thing...
However, another very significant factor is the load you are putting on the rock and blade with your gravity feed. You don't want to use more weight than what is necessary to transport the rock through the blade. Excessive weight will cause your blade to glaze and may cause even more severe problems such as dishing. Check the weight and make sure you are not using more than is needed to move the rock.
As has already been noted by another responder to your post, increasing your motor horsepower will not necessarily increase your blade rpm (unless it is lugging due to the motor simply being too small for the load). AC motors are available in different rpms, so you may be able to increase the blade rpm by changing to a faster motor. You may also be able to change the drive ratio by using a different pulley on the motor. If you do increase the blade rpm you may also need to increase the coolant flow. There's a number of interrelated variables and factors that need to be considered.
If you are having to dress the blade very frequently when cutting harder materials it sounds like you are experiencing glazing issues. Some more information would be helpful in analyzing your set up and problem. At what rpm does your blade currently spin? What is the manufacturer's recommended max rpm for the blade? Be sure you do not exceed this rating if you start playing with motor speeds and drive ratios.
If you don't have your problem figured out yet get back to us here and we'll try to help.
From Bob Keller - June 02, 2008 at 11:58:09