Guys need to get their facts straight before deciding it's one or the other.
For one: http://www.thirdgen.org/1989-chevy-camaro
A 1989 Iroc can have a variety of engines, including a weak ass 170hp/255 torque 305.
To simply state that it has a specific engine, like the other answer does....is an uneducated answer, at best.
A 1978 Trans Am, could have the 403 engine, with 185~ hp, and 320~ ft lbs of torque. Or the 400 with 220 hp/320 torque. More than equal to the engines available to the 89 Iroc.
In fact, you could pair the two cars up with almost identical engine specs, nearly identical weight, etc. Making for practically an even race, as far as power goes.
Without knowing the exact engines, specs of both cars, and driver ability of cars, it's pointless to even ask this. Too many variables.