Read the how to articles 90 primary and secondary injectors orings question...

[Corvette95]

Thanks! Pete is going to port them for me next week.

Originally Posted by Paul Workman

To be clear, ONLY the 1990 PRIMARY injectors ALSO have a O-ring in the injector bore (in the Injector Housing). Whereas, the secondary injectors are sealed ONLY at the tip - pressed against the boss which is situated in the middle of the secondary runner.

For this reason, when max porting is done on the 90s ONLY, the O-ring boss at the tip of the injector (in the PRIMARY runner) can be removed* entirely as the O-ring at the tip of the PRIMARY injector is redundant. Instead, the O-ring surrounding the injector body at the top of the PRIMARY injector provides the necessary seal.

HOWEVER, IF the motor is to remain stock and not ported, then both the primary and secondary injectors will have O-rings at the tip, AND the primary injectors will also have a second O-ring at the top of the injector body (found in a groove cut into the injector bore about 5mm below the mouth of the bore (as Hans (ccmano) said.

*This is exclusive to the 1990 IHs only: An argument can be made that the air flow in the 90 LT5s can be slightly better in fully ported Injector Housings than later Zs, b/c the obstruction posed by the primary (only) boss can be removed entirely when performing maximum porting.