help with 99 altima performance?

[youknowmeehan]

So my friend has a 99 altima. We have so far only put an intake and catback exhaust on it. We have headers coming in the mail. We want to keep the car non aspirated. Does anyone have any advice on things to do to make more power. I can't find any info or websites on bigger pistons and throttle body. Can anyone give help on how to make more power out of this car. Anything is appreciated think you.