[zonker]

in my experience, factory intake systems are designed to address four concerns... emissions, drivability, economy, and nvh.

for most modders, be it eco or hipo, the nvh concern can take a much larger back seat to the factory engineered system, so there is usually some room for improvement.

as a general rule of thumb, unrestricted airflow ahead of the maf sensor serves to improve both economy and power.

it's what you do between the maf/vam/iat sensors and the throttle body that makes things more interesting, and can give quite varied results from a modification.

for example, the white rag gets better mpg from a 2.25" dia. aluminum tube (with 144cc injectors) between TB and MAF, and gets more power when i use a 2.75" dia. tube (with 168cc injectors). the smaller tube increases air velocity thru the maf sensor which advances timing and enriches fuel (which i lean back out with the slightly smaller than oe 152cc injectors).