engine mods

Can anybody tell me what mods I should make to my L240 motor to take me up a stage or two in engine horsepower.

I am currently using the car for club sprints and hillclimbs.

All suspension mods are complete and it handles exceptionally well. Unfortunately I get my arse kicked powering out of corners and down long straights.

The motor was rebuilt before I got the car a few years ago using pretty much standard parts except for the addition of the N42 big valve head and a decent set of extractors. I fitted a two and a half inch street legal straight through exaust.

Limited funds at the moment prevent me from taking the car to an engine tuner.

I am quite capable of doing all the assembly work myself.