I race a 1995 camaro Z28, stock LT1 engine with comp cams XFI cam swap, 1.6 rockers, 58mm throttle body, 30lb injectors & open long tube headers. How much nitrous can I spray without retarding my timing?

 

Did the "tune" included more aggressive than stock timing? Did the tune desensitize the knock sensor/retard? What plugs are you running? Stock extended nose plugs do not play well with nitrous.

Why don't you want to retard timing? You do that externally, so it doesn't affect performance off the bottle. An ignition box like the MSD Digital-6 Plus is a good. Helps insure a healthy spark at the increased combustion pressures generated by nitrous, provides a cut spark rev limiter, and has a timing retard applied only when nitrous is activated, leaving your timing alone on straight motor.