Launch Rpm Vs. Stall Speed

[ciara]

I am running a powerglide tranny with a transbrake in my car. I have a 4000 stall convertor in it recommend by the manufacturer based on my engine set up. My question is how do I determine the best launch rpm? I have heard about true stall, flash stall, etc. The convertor maker said to launch 500 rpm under the stall. How do I determine the actual stall speed and how do I use that to get the most out of my launch. When I launch at 3500 the car goes hard and straight with no wheel spin, but I want to maximize my launch.