I was thinking of installing the KnN High flow air filter to my 99 5.9 Durango and was looking for some feedback from those that have. Do you notice the additional horse power? Is there any substantial fuel efficiency? Dose it sound better? Is it really worth it?

 

I have run the cone style that replaces your factory air box on several different cars and have not noticed any performance gains or fuel economy but they are washable and will last the life of your car. There is a noticable intake noise with them, whether or not it sounds cool is up to you. I am not replacing the factory air box on my 04 Hemi Durango but I will buy either a K&N or Fram Airhog factory replacement filter for my stock air box. They are washable as well and I don't have to deal with the intake noise.

 

I don't have the KnN filter but I have a similar setup (found on ebay for 50 bucks). Anyway even with my ghetto rig I could tell right away there was a hp/torque gain (could be all in the head). Any time you give your car more air especially colder air you are going to see slight performance gains. I noticed a slight increase in my mpg, about .5 to 1 mpg, which comes out to 25 more miles per tank. So if you think of it that way it will pay for itself. I thought mine was completely worth it, however mine didn't come with any sort of water/heat sheild which I believe the KnN comes with so that's a plus. As far as sound goes there is a bit of difference at lower RPM's mine has a slight hiss sound to it then at higher RPMs it gives of a little roar. From what I understand that sound is produced by the actual filter so it could vary from filter to filter. It won't increase the sound like a good muffler and exhaust system would do but there is a little more sound. Easy to install too. Hope that helps.

 

better off picking up a CAI. http://www.intenseperformance.com real good deals

 

Does anyone know of any flow data on the stock factory air box? It would be interesting to see how restrictive it is.

Here is approximately what the new Hemi should flow 350 CID x 6000 RPM = 2,100,000 / 3456 = 608 CFM
350 CID x 4000 RPM = 1,400,000 / 3456 = 405 CFM
350 CID x 3000 RPM = 1,050,000 / 3456 = 304 CFM
350 CID x 2000 RPM = 700,000 / 3456 = 203 CFM


These calculations assume 100% volumetric efficiency which is acheivable in a race motor, the new hemi is probably at about 85% VE so you can safely subtract another 15% from my CFM calculations. If you have a 4.7 replace the 350 variable with 287. Most any stock replacement filter is going to flow 300 CFM. It looks like thatere should be no HP/torque/fuel economy gains until you get up into 4000+ RPM range, the 10-20% hp gains KN and the others claim may be true but that up around 5000+ RPMs.