i have a 305 tpi a bit modified and i have 8 injecton of a mustang 89 they seems to fit intoo mi stock intake how do i know if i should put them?

 

Well if the injectors are from a stock Mustang V8, then they'll be 19 lb/hr. They should be orange if that's the case. Which wouldn't make a difference from your stock injectors. But I'm pretty sure they would work, in case you ever need them for a backup set if one of yours fails or starts leaking.

 

im sure mine are less than 19 i guess 13psi by the hayne book
and yes they are orange!on the question when yo need to upgrade the injector with smalll modification of after 800whp?
understand ehat i mean?

 

Well the 2.8's/3.1's, the V6's, got either 14 or 16 lb/hr injectors. And I'm sure the V8's got larger injectors. So yours SHOULD be right around an 18 or 19 lb/hr or so.

My experience here is with a Ford...but 19 lb/hr's will support over 300 horsepower. But once you start getting over 300, bigger ones will give you extra power. I don't know what the injector sizes are on the Chevys, but you could probably benefit from some 24 lb/hrs.