I am looking at converting my S40 T5 from the stock airbox and panel filter to the Focus RS/Volvo P1 diesel airbox with cylindrical filter as described in two good threads by Blanca and CentaX over on C30crew. I have an Airtec upper inlet plenum that I've wanted to install for a couple of years but it doesn't work with the stock airbox (despite what they told me when I ordered it!) so I've been looking at alternatives ranging from open cone filter to Spectre inline airboxes to the Focus RS airbox. I've settled on the Focus RS airbox because I like the OEM look (and in fact, it is OEM for diesel S40's) and the fact I can pick one up in a wrecking yard because they still used the same basic airbox on 2013 and later Focuses and Escapes. I'll document the changeover once I do it since I plan a few changes from the C30crew examples.
Anyway, on to the point of this post. I was looking for flow data to compare the OEM panel type filter for a stock S40 T5 with the seemingly much larger OEM cylindrical filter of the Focus. Our OEM filters is about 9"x8" and the Focus filter is 6.25" in diameter and 8.25" long. I can't find flow info on the OEM filters so I went to the K&N website just so I could compare filters with the same media to each other. Of course, they don't have data for the panel filter that fits our cars but they do have data for one that is close in thickness and in surface area, the 33-2042 (ours is 33-2873) and uses the same amount of oil to re-oil it (32 ml) so it should give similar results. The Focus filter is E-2993 (uses 56 ml to re-oil, so seemingly a much bigger filter) and they do, in fact have data for it. The most directly comparable data for these two filters is the airflow at 1.5 inH2O pressure - they describe it as the "amount of airflow before the air filter creates restriction of more than 1.5 inches of water pressure" - and the panel filter achieves 498.9 cfm while the cylindrical achieves 181.6 cfm. Both say tests were conducted in OE airboxes - the panel filter is used in a bunch of GM products with engines ranging from I4's to V8's so I don't know what the airbox looks like for that filter. These results leave me quite confused since I would think the bigger filter would be more free flowing and achieve a higher cfm at the same pressure drop. Am I missing something here? I saw similar numbers for other Focus replacement filters so I don't think it is an anomaly for the K&N test. They also provided restriction vs particle load data but they were done at different constant airflow rates so they are hard to compare directly. What I'd really like to see is restriction vs cfm data over the cfm range of interest for our cars but I don't think I'll find anything close to that.
Just to confuse the situation a little more, in my research on the subject I came across an academic paper that compared the same style K&N filter with an OE filter and found the K&N filter to be more restrictive but provide better mileage and acceleration. So maybe less restrictive isn't better?
Any thoughts on this issue? Thanks!
Anyway, on to the point of this post. I was looking for flow data to compare the OEM panel type filter for a stock S40 T5 with the seemingly much larger OEM cylindrical filter of the Focus. Our OEM filters is about 9"x8" and the Focus filter is 6.25" in diameter and 8.25" long. I can't find flow info on the OEM filters so I went to the K&N website just so I could compare filters with the same media to each other. Of course, they don't have data for the panel filter that fits our cars but they do have data for one that is close in thickness and in surface area, the 33-2042 (ours is 33-2873) and uses the same amount of oil to re-oil it (32 ml) so it should give similar results. The Focus filter is E-2993 (uses 56 ml to re-oil, so seemingly a much bigger filter) and they do, in fact have data for it. The most directly comparable data for these two filters is the airflow at 1.5 inH2O pressure - they describe it as the "amount of airflow before the air filter creates restriction of more than 1.5 inches of water pressure" - and the panel filter achieves 498.9 cfm while the cylindrical achieves 181.6 cfm. Both say tests were conducted in OE airboxes - the panel filter is used in a bunch of GM products with engines ranging from I4's to V8's so I don't know what the airbox looks like for that filter. These results leave me quite confused since I would think the bigger filter would be more free flowing and achieve a higher cfm at the same pressure drop. Am I missing something here? I saw similar numbers for other Focus replacement filters so I don't think it is an anomaly for the K&N test. They also provided restriction vs particle load data but they were done at different constant airflow rates so they are hard to compare directly. What I'd really like to see is restriction vs cfm data over the cfm range of interest for our cars but I don't think I'll find anything close to that.
Just to confuse the situation a little more, in my research on the subject I came across an academic paper that compared the same style K&N filter with an OE filter and found the K&N filter to be more restrictive but provide better mileage and acceleration. So maybe less restrictive isn't better?
Any thoughts on this issue? Thanks!
