1 - k&n conical filter
2 - ngk irridium spark plugz
3 - freeflow system which includes headers manifolds and exhaust
4 - any kind of power chip...say tri-phase , heard it boosts performance by 20 % so consider atleast 10 % increase which is also too much
5 - porting and polishing
6 - to reduce the weight ...you could modify the body of your car using fiber kits dat is fiber plastic .
7 - u could get a turbo with a nice intercooler
8 - if all this also makes u feel your car is slow...then sell off the engine , and buy a new engine and go ahead with engine transplant ....worked for my car .
P.S - if u get conical filter for yourself , make sure u get a custom made pipe to for cold air intake , or else your car will be slower than what it actually is ...pm me if any query...im bigtime into cars....