WHP will not break the transmission. Torque is the problem. A 600 whp, 450 ft/lb car is a lot less likely to break the tranny than a 600 whp, 650 ft/lb car. We've seen the ECU torque limiter set to around 500 ft/lb. It's going to take bigger turbos and full ECU tuning with the torque limiters removed before we find out.