It depends on the weight of your car and what kind of traction your getting, its usually torque (from getting traction) that will break them. But an 8" will usually take 350-375 on street tires if its in good working order.
1991 LX Mustang 347 C4 combo 11's with the AC on.
1984 Mustang GT 460, Powerglide "Still putting it together" hoping for 9's !!
<font size=-1>[ This Message was edited by: dfree383 on 3/18/06 3:19am ]</font>
Ran some 1.38's with my old Maverick 8". Swapped in a 9" not long after...never had anything wrong with the 8" but I just needed a better gear selection. 4.62 was too low and 4.11 was too high. Had to put the 9" in for the 4.30's and it worked pretty good. Car was all stock suspension back then...with a 393w/powerglide.
ive put 530hp at the fw into an 8" with mini spool and with 26/10.5 et streets with 1.5 60ft times only damage was twisted axle splines on axle which had been cut and resplined other axle still like new