Originally Posted by wemay
While on throttle, every vehicle can take in more air than a typical filter will flow. The less restrictive a filter, the more air that's sucked in.
Nope, that's backwards. Most filter's CFM rating is significantly higher than the flow rate for the TB. For example, I had a 75mm throttle body on my 302, which was mounted to a TFS-R, feeding a set of very heavily massaged GT40's. It was connected through the factory intake plumbing, which was ~90mm in diameter, to the stock Fox panel filter, which was about 12" long by 9" wide (going by memory). IIRC, the flow rating for that panel filter was ~1,250CFM. The maximum that TB would flow was ~920CFM without forced induction (N/A application) and at ~325HP (flywheel) I was consuming nowhere near that.
As I said earlier, you can easily verify if the filter is a problem using a vacuum gauge plumbed into the box or plumbing on the clean side of the filter. The K&N filter restriction gauge is probably an ideal fit, as it is both very sensitive (much more so than the typical diesel ones) and locks in place at the restriction level, so you can go out, do a WOT run and see if it showed any restriction.
Here's a CFM calc:
https://racingcalcs.com/cfm-cubic-feet-per-minute-calculator/
If I plug in my 392, and get ridiculously generous with the VE, putting it at 90%, at 6,500RPM, my air requirements are only 663CFM. The factory filter flows 1,080CFM.
EDIT: Actually, we can get much more accurate here, as they have a displacement + VE to HP calculator too, which also gives CFM requirements:
https://racingcalcs.com/engine-horsepower-calculator/
So, my 392 makes 475HP, so VE is 88%, which pegs my CFM requirements right around 650, meaning the factory filter is VERY generously sized.