Embaressingly enough... I'm a former F-body junkie; so I can speak with relative knowledge on the subject. The GTA and IROC-Z is exactly the same car with different interior and body front quarters/nose shape. The GTA is was little heavier in 89 & 90 b/c they put more 'goop' on it for looks (goop meaning abs). As for powertrain, the put both the 5.0 throttle body inj T-5 5 speeds with 3:23 rears, and 5.7 TPI TH400 autos with 2:?? rears.
All it really takes to beef them up to compete with a 5.0 or 4.6 GT is a 3:73 or higher rear and a few mods to the 5.7... I dropped a 350 4bbl carb in my old 87 Z-28 and popped some fresh 3:73's in it and the car was a beast...
And then I bought my Cobra and woke up to reality.
Anyone interested in an 87 IROC-Z??? New rear... quick. Only $1500
