Wow, that car brings back a lot of memories! The 85 GT was one of a bunch new 5.0’s I had back in the day (82GT, 83GT 85GT, 93LX5.0, 95 Cobra).
Here’s me racing her when she was brand new (yes, brand new - ha!):
I did mostly test/tune, but I bracket raced a couple of times and actually won once:
First off, unless you’re absolutely bent on racing it … DON’T MOD IT! Not too many 85 GT’s left that haven’t been torn to pieces.
But if you’re def gonna race it, this is what you should do first:
-Replace the stock 2.73/3.08 7.5" rear axle with an 8.8" 3.55
( I broke my 7.5 on the starting line at LVD, tow back to Schtd’y was $250)
-Get a beefed up transmission
(2nd and 3rd gear synchros are weak in the T-5, I learned how to remove/replace transmissions because of this car)
-Get an Edelbrock Mani if they still make them, shorty headers, and a good exhaust system
(this combo worked especially well for this car)
I ran low 14’s on street tires with that set up, which was good considering it’s a high 14/low 15 sec. car stock.
Good Luck!