well, that really depends on several factors...
(1) What RPM do you typically or are planning to launch the car at? I would start lower first and work your way up, dont just launch it at or near redline on the first tun...
(2) How many miles are on that rearend as it is? The older the rearend the more wear it has on it...
(3) How often are you or have you been to the track? After each pass you make, the likleyhood of breaking a rear axle or the like goes up...If you are just a "once in a while" racer, maybe a few times a year, you should get quite a bit of time out of the rearend...if you intend to go out there every week, you will be needing to build up that rearend as much as possible or it wont last very long on DR's...
If this is a one time event, I don't think youre really making enough power beyond stock to significantly hurt anything so long as you don't do anything stupid lol...
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'05 GT - Borla Catback, Koni Adjustable Shocks/Struts, Hawk HP+ Brakes all around, Steeda Front Sway Bar & End-Links, Hoosier A6's on Enkei Race Wheels, Royal Purple Fluids
'07 F-150 Ext. Cab XLT Flareside - 5.4 Triton - Roush Dual Exit Cat Back