Originally Posted by ZeeOSix
Originally Posted by OVERKILL
Originally Posted by ZeeOSix
Originally Posted by OVERKILL
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.
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.
Regardless of how much CFM the throttle body is rated to flow, if the filter (and intake tubing) adds some flow restriction (they all do to some degree), then there is a corresponding delta-p across the filter and ducting which reduces the absolute air supply pressure at the entrance of the throttle body by that amount - talking about NA engines here.
If you compared a free flowing filter to a flow restrictive filter, you'd see an increased delta-p on the filter restriction gage across the filter at WOT with a more restrictive filter, and should also see a corresponding HP loss on the dyno.
Throw a nearly clogged filter in the box and see how much filter delta-p there is and how much HP is lost at WOT. Any time there is less absolute air supply pressure at the entrance of the throttle body, there is less air flow volume going into the engine, regardless of how big the throttle body is.
Right, but again, this is all easy verified with a restriction gauge, which is why I recommended trying it. It's the easiest way to tell if the filter is in fact a restriction and also doubles as a filter change interval device once in place. I've run a sensitive vacuum gauge on the back side of an airbox before to test with very generously sized plumbing when trying to ensure there were no restrictions on a pretty deep breathing N/A 302, blindly tossing a K&N on something because of a notion that its "mad flowz" is going to be of benefit without actually testing beforehand and giving up the superior filtration of the stock filter isn't doing one any favours is my main point here. There's an actual method, which both of us appear to agree on, in determining if an upgrade to the air intake tract is required. One cannot blindly and universally state they there is or is not an issue without following that method.
If you want to do a complete analysis/test, put an absolute pressure sensor for ATM, one for absolute pressure after the air filter and one for absolute pressure at the entrance of the throttle body. That way, you can see the complete pressure drop in the system from the ATM to the throttle body. As mentioned, it's the absolute pressure at the throttle body entrance that determines how much air flow is going into the throttle body. Every intake system and air filter combo has a pressure drop (delta-p) from air flowing through it - and the higher the air flow volume the larger the pressure drop. You'll always get more HP from a less restrictive system because it will allow more air flow volume to the throttle body due to less delta-p pressure drop ... again, only talking only about NA engines.
I don't disagree, but I don't think that's a reasonable proposal for Joe DIY wanting to find out if his air filter is restrictive. A simple sensitive restriction gauge like the Donaldson unit K&N sells should be sufficient for the task of determining if the filter is an issue. The plumbing, while germane to this discussion, is a separate issue. In many cases, silencers fitted into the intake tract can be easily removed to make it more free-flowing. In my testing, since I was using large diameter aluminum piping with minimal bends, there was no need to analyze beyond the filter housing.