yeah..yeah..before anyone crucifies me let me explain myself...
As the adage goes "No pain, no gain"..the same argument applies to performance. The only things that are truely bolt on on a car are stuff that improves its appearance. Performance is a different aspect.
I agree that free flow exhausts, high performance filters and stuff do improve the performance but if you need the same level of trouble free and convenient operation as a stock system it involves a lot of work.
As has been mentioned on this thread an engine is a system, and the system has been tuned in a company. Now the minute you and I replace a component we are changing a system. So we need to do something or the other to get the system back into shape.
About stuff like ground wires and stuff i agree that by themselves provide very little gain but they sure do complement a system that has been modded for performance and improve the feel. Take a look at this site...
SUZUKI SPORT Parts Information / SWFT. I understood only the graphs

....here is the one for a street muffler...

News Release
It shows not much increase in bhp but the curve is much smoother.
Not withstanding this i do have a FF exhaust and a universal air filter in my car and am still searching for the feel i want.
Thats my two cents for now...
And for all the guys who have been putting in great info on this thread...chetanhanda,ananthkamath,v1p3r,nextlevel3 50z..etc..
- Shibu