Call a custom grinder like bullet...give them specs and goals for the car.I ran an xe 268 in warm 340 and it needed a converter with more than stock stall regardless of what comp say.In all fairness i was running 3.23 gears and a 27" tire but it was lazy at lo rpm until i installed a dynamic 9 1/2 converter.
From mid range up the power seemed limitless!
