Thread: Open cone intake clarification

The CFM flow rating is how much the filter flows before it starts pulling a vacuum.

Originally Posted by darkhorizon

The CFM flow rating is how much the filter flows before it starts pulling a vacuum.

Technically,

Anytime there is fluid flow there is either a vacuum or a pressure rise.

Originally Posted by mechguy

Technically,

Anytime there is fluid flow there is either a vacuum or a pressure rise.

Well, I suppose that I should say "significant" vacuum.

K-N rates their filters at 2 or 3 inches of mercury, which depending on what math you follow could be twice or 3x as much as the zzp test.

The last air filter conundrum I ran into was on a NIC car I was building, where the owner refused to go with my "go to" AEM dryflow filter as it was too large. He ended up buying a bunch of KN stuff that was rated at 800-1000cfm, only to later find out it was causing major KR (wideband stayed the same). Removing the air filter from the system would eliminate up to 4KR in some cases.

So he then looked at the ratings a bit closer via some emails to KN, and found out that the flow ratings were done in situations of IMO high restriction. In theory a filter could flow unlimited amounts of air, but the vacuum, aka restriction, it pulls is going to go up significantly.