Are there any free or do-it-yourself mods I can do to a 1990 305 TPI? Can you guys let me know and also how to do them... thanks.

 

you can eliminate all of the emisions crap, that will free up some power and wieght...you can also take your whole a/c system out, that will also take about 40lbs off the front of your car, and will free up some hp also...all you gotta do is disconnect your airpump and take it all out, and take your cat out too....and for a/c, you pretty much take it right out of there, and gett a false pulley or reroute your belt system...there aren't many FREE ways to get more power, but there are some inexpensive ways...

 

make a cold air intake or atleast gut the air boxes that house your 2 air filters.

port your intake and runners

 

http://www.gmtips.com/3rd-degree/dox/tips/tips.htm

That may help you out.

Botch

 

bump the timing a few degrees and run good gas, throttle body bypass, 160 degree thermostat (cheap), mold your own airfoil, ram-air from behind the fog lights.