Stall-speed numbers are listed primarily to rate a converter’s performance level. Typically, the number assigned (2,000, 2,500, 3,000) will let you know the ballpark stall-speed rpm to expect from the converter. If a 2,500-stall converter is selected, matched with the PROPER COMPONENTS you should be able to foot brake stall the converter up to about 2,500 rpm. Lighter cars weighing 2,800 pounds and under will typically stall a little lower than the above-mentioned numbers, therefore you should choose a converter with a higher stall number for optimum performance.
adding another 1000 rpm's to your stall # will not nessacarily mean that it will give you another 1000. it will give you more but it will react to the trucks, overall build, gear ratio, tire size, weight, engine components, etc,etc,etc,