I was twisting input/ output shafts at around 800 hp. 3700 lb car, mid nines 1/4. Went to A&A input/output shafts and had zero problems after that. The car eventually was running high 8s @155 at 3700 lbs with a 3.50 rear gear. Engine was making some good power and had a lot of weight and gear ratio to fight. Trans was reliable and predictable.