* TPI (Tuned Port Injection): This was the more common and powerful version. It typically produced around 230 horsepower.
* TBI (Throttle Body Injection): This less common version usually produced around 170-180 horsepower.
Therefore, without knowing the specific fuel injection system, you can't say for certain. But 230 horsepower is a good estimate for most 1989 IROC-Zs with the 305 engine.