With the turbo car, the stall also has to get the turbo spooled.
The gear alone will change the flash stall of the same converter by placing more or less load on the converter once the car launches. You want as tight of a converter as you can stand to get the turbo spooled and then gear the car to be in the correct rpm range through the traps...........
Just to add to what Dusty said, the stall not only has to get the turbo spooled, but launch the car w/o breaking the tires loose.
The RPM through the traps needs to be within the power band where the car is still pulling. In my racing experience, trap speed does not win races, E.T. does.
It usually takes us a season of racing to get a newly built car [and driver!] to get consistent enough to win. Of course it is not only the converter and its efficiency, but gearing, tire size, power band and other factors that all interact for the optimum performance desired.
In our experience over the years, we find that most owners start with a converter too tight. I would rather tighten a converter, than loosen it.
I did forget to add another comment, sorry.
Over the years I have used MANY different brands on converters, and worked with many different companies.
With that said, my experiences with Dusty, Chris and PTC have been the best from all perspectives - cost, performance, customer service and just plain honest dealings. Their experience with converters for turbo cars is better than any I have found.
Do NOT cheap out on a converter, it is key to optimum performance.