not just that, stock/original manufacturer's oem parts, piping and etc are build and design to meet the strict emission control set by this global agencies, so call the environment friendly rules. and car manufacturers design and build the engine and everything to meet various aspects such as production cost, emission like i said, fuel quality in different region, NVH, comfort and etc. hence, there are reasons why aftermarket parts exist. for example the stock exhaust, piping is smaller, with cat-con, with extra large restrictive muffler and midbox to meet the NVH and emission standard. it doesnt mean larger piping and free flowing exhaust is bad, its just more noisy, less comfort and not environment friendly. if according to that idiot who keep saying oem parts are god. we do not need this forum anymore to discuss modification. just drive stock car like those uncles. everything that is engineered in this world be it cars, phones, electronics devices and etc, in stock/original condition, we engineers always have to ensure that there is some room for error in its design efficiency or capabilities. so meaning put a car for example, the engines in stock form are design in a way it is less power and etc for room for error like worse fuel quality in other countries. that is why u hear ppl say re-tune the ECU gain power and torque, its not gaining, you are just tuning the engine to perform what it is capable to do with our better fuel quality in this region. if u have more basic mods like free flowing exhaust and better air intake than stock, u even gain more. as simple as that. you gain power and torque thru burning more fuel and air, sure higher FC lar. but why some ppl drive a modded car gain better FC? if you drive the car the normal way, you could lead to better FC coz you will be ez on the throttle to gain certain power or acceleration that you need to throttle more before you mod your ride. simple. but trust me, that jayraptor will come with even more awesome theories to reply here. 

Waste of time IMO

Gouki,
Can't u type in paragraphs?! So difficult to read with my old eyes...