unfortunetly, there isnt much you can do for a G1. Do a tune up, plugs, cap rotor, fuel filter, air filter. that should help alot. also depending on your milage, you might have a clogged cat converter. I remember I had the same issue with my g2, and putting in a new OE cat gave me a ton more power (through the entire rpm band).

as for a new header i dont think anyone makes them for your car. I was told that a 88-91 civic d series header would work, but then again alot of parts were differnet on the intergra's D-series so you would need someone else to give u some input on that.

good luck