I got a 03 4.8 turbo silverado will zr1 injectors fit without any adaptors and spacers

 

No not without a spacer, the spacer isnt the problem. Ive dynoed back to back with/without a spacer and there is ZERO difference in power on the dyno.

The problem with the ZR1 injectors is that they spray the fuel at an angle. The supercharger on the ZR1 put the injectors farther out, so it has to spray the fuel at an angle back at the valve. When you put these injectors in a typical LS engine, you will spray the fuel at the cylinder port wall and not the valve as intended. I typically run LS2 injectors, FAST has versions of 34/46/57 lbs/hr. They also have the LS3 injectors, that require a spacer that come in 41/50/65/85 lb/hr.

Although the easiest swap is typically the 8.1L marine injectors, but they are only avaliable in 42lb/hr.