Intake air flow modification

[MetroMPG]

Originally Posted by rh77

Let's break it down -- what happens if the same amount of air has to travel through a smaller tube? The air velocity increases -- like if you put your thumb on the end of a garden hose.

i think that comparison may be misleading.

- the intake air isn't travelling through a smaller tube, it's just going through a smaller opening, into the original size tube. i don't think the pressure "advantage" is maintained. svoboy essentially pointed this out when he mentioned the intake manifold is different (smaller volume/cross section) in the more efficient motor. if you don't change the manifold size...

- blocking a garden hose pressurizes everything upstream of the block; adding a restrictor plate doesn't do anything comparable to the ambient pressure. and i'm not sure if the effects of a pressurized hose can be compared to a de-pressurized (vacuum) intake manifold - though i could be wrong.

- also, the garden hose is expelling its contents (water) into a different medium (air) - an apples-to-oranges comparison. if it were expelling its contents into water (a narrow opening into larger volume), the velocity effect would be quickly diffused relative to air.

sorry, but i still don't see how adding a restrictor plate to an otherwise unmodified engine would help.