Port and polish the manifold. That pulls more air in and pushes more air out, then when,you start adding more air you have to think about air/fuel ratio. To much air car won’t run, to much fuel the car will try to stall or run super rich which then means more carbon deposits and build up.
Or, put a cold air intake on it it will Atleast draw out another 30-60 hp. Also fuel with a higher octane, for example,if you use 87 go to 91 and it will help the engine run cleaner with less hesitation and more response