Sprag. The transmissions sprag would likley fail before the converter does. If its for good powe comanys have larger sprags. Evan ati the company who started the spragless setups said that the sprag still works for most apps. If its for a turbo app they would likley recomed the same converter I have. Ati fuel blown 9 or 10" has a oversized sprag very tight converter for boost. I've had mine for 4 seasons and just checked over the winter it was perfect inside. And with arround 950 to 1000 at the motor I figured something would have been wrong after 4 seasons on it.