[LostCause]

I'm not sure why you are trying to increase your fuel economy, but if it is for economical reasons then it will take an extremely long time to break even. $395 can be spent much more wisely in other proven modifications or towards fuel.

Changing the length of the intake runners will probably be detrimental. Intake runners are sized based on Helmhotz resonance. By timing intake pulses (caused by valve closure) to valve overlap, cylinder scavenging is improved. The runners should already be sized to either remove an inconsistency in torque (usually ~3000rpm) or to improve low-end torque (<3000rpm).

Porting and polishing are generally undesirable in the hypermiling field. It has a tendency to increase hp by raising peak torque - the opposite of what is generally desired.

Additionally, the VTEC-E motor is set up excellent from the factory for fuel economy. When you are only developing ~12hp at cruise, you don't need large pipes or high flow rates. The major constriction, the throttle plate, is already taken care of through lean burn.

Lastly, modifying your vehicle permanently will adversely affect your car's resale value. Once you customize an automobile, you make it much less desirable for the common man...who will probably not appreciate your taste. Your car has inherent worth. By maximizing its resale value, you'll save money. If you are concerned about costs, focusing on the whole picture will see you furthest ahead.

- LostCause