well if you get 166000 miles out of a tranny, its beefy enough for me. especially if it has 325 hp to push though. my auto has 70k on it and its shot. bands are slipping and the tc is done for. so feel good to more than double that

 

Mine was still working fine when I took it out of my 4,000lb car after ~35K miles and 733rwhp with over 800ft-lbs at the rear wheels. That said, most of the miles were on the street and making less hp. I switched to a TH400 because I am upping the hp and want to do some bracket racing. It's damn near impossible to be very consistent with the T56 and a setup like mine. For one thing, I wouldn't even consider powershifting it. But it is a damn strong tranny. Pity the rear end isn't as strong, or the DS for that matter.

There is no "magic number" for the amount of hp and torque the transmission can handle. It is rated at 450ft-lbs, and at that level should be near indestructible unless abused. You can buy a version from Tremec rated for ~750ft-lbs. I got a quote of ~$25,000 for a custom version of that tranny for the 4th gen. Needless to say, I passed on that.

BTW: the LS1 and LT1 T56 are the same, AFAIK.

Rich Krause