At what point (HP, Mods, etc) is it necessary to upgrade to a larger Injector size. I have a 99 LS1, mild cam upgrade, headers, intake/TB upgraded, springs, but stock bottom & Heads & stock injectors. I don't think I need larger injectors or would I benefit from moving up ? thanks

 

You should be OK with those mods but the way to know for sure is to check the injector pulse. If it is at 80% or less, you are fine. *0% to 90's is acceptable. If it gets to 100% or above, you need bigger injectors.

 

When you get heads/cam upgraded is typically when people upgrade their injectors. Even a fuel pump upgrade may be required. It all depends on your setup.

 

my car with Port T/B, TSP 233/239 cam and headers is at 98% duty cycle at 6800rpm... stock everything else. Tuner said me need injectors now

 

It is not only injector size but one need to pay attention to fuel pressure. Our systems have a regulator close to the tank. This does not insure steady pressure at rails. So proper procedure is to detrermine what your fuel pressure is at WOT, if adequate and cycle over 80%, then yes injector time.
Yours being a 99, I would consider a fuel system upgrade (pump, harness and injectors). IMO, 90% of injector swaps are not needed due to bad fuel pressure, I cured that by installing a FPR at the rail with return line, I made the return line to go into the nitrous stand alone. This allows me to run SVO 30lbs to 550 rwhp +

 

when the injector duty exeeds 80%