Here's a common way of upgrading an NA engine, although in a general way and not specific to any model and do not need to be strictly followed:
1. Good lubricant, less friction means more power.
2. Intake and exhaust, note that drop in filter is better for light mod since open pod/cone filter draws in hot air = less power, unless your car is for track racing where it move fast enough to ram cold air in your engine bay everytime or you can afford cold air intake system.
3. Adjustable cam pulley. can adjust for predictable power, but if you have variable cam timing, might as well leave it, better for everyday driving.
4. mild cams, extra power with stock ecu.
5. use lightened flywheel
6. go for aftermarket programable ecu, and throw in racing cam inside, as high as you can accept.
7. rebuild and balance the whole engine, do a 3 angle valve job or 5 angle one, port and polish the head.
8. do anything to increase your compresion ratio, but with malaysian's ron97 fuel i don't see too much increasement in power without suffering from knocking :D
thats about the general stuff you can do with your engine, other performance gain that do not have anything to do with the engine would be:
-use a good clutch system
-if you got the money and willing to learn, get a dog engagement gearbox
-use smaller size/lighter/balanced rim
-basically make your car have better power to weight ratio..
well, hope that helps...
