My '89 is due for its overhaul soon and before I get the car put together I need to know what kinda of results I will see and if I will have any issues. The car is a '89 GXL auto with 125k miles. The car itself is in excellent shape and the motor shows no sign of weakness and runs at full potential. The auto is being replaced with a S4 TII trans and replacing the flex plate with a almost as light racing flywheel with the counter wieght still on. The crossmember and the rear diff are being custom fitted to fit the TII trans and drive line. Also I'm replacing the cats with a straight pipe but I've heard the S5 motor won't have issues with back pressure. Will I have any problems and what kind of power will I be looking at getting back seeing as how I'm only getting 105 rwhp because of this auto?

 

You might consider removing the iron box exhaust collector & get a header.
A header is about the best bang/buck bolt on, and if you do any other mods (intake or ports) in the future it will amplify them.

Check out the header pics & sound clip links in my sig below.

 

Agreed. Adding a racing beat collected header in before my stock catalytic converter on my streetported engine and base model NA produced a .04 g acceleration improvement in the first three gears. I still need to get out to some clear pavement to do a quarter mile run to see how it changed my base time, which was 15.5@96 the other day on stock exhaust.