Foam pre-filter with normal paper filter

Status
Not open for further replies.
Joined
Oct 12, 2010
Messages
902
Location
GA
Reading about filters and efficiency has got me wondering if there could be any benefit to adding an oiled foam pre-filter to a standard OEM style paper filter. Especially as we know that modern EFI systems can deal with intake restrictions without harming efficiency.

My idea is to get a sheet of foam filter material, preferably urethane with high PPI count, and wrap it over the fresh air side of the paper filter element. This way it will catch the fresh air first. Since the standard paper element will still be there, the worst that can happen is that it will do nothing. If the foam looks like it's picking up dirt, then so much the better. I also have a restriction gauge on the housing.

Please excuse my tendency to over-think and over-kill this. I'm an engineer after all
smile.gif
 
I'd only add pre-filter foam if and only if I'm operating in an extremely dusty area. Otherwise: I'd use what the factory comes with (pleated paper filter? you bet).

Q.

BTW: nothing works as good as N-95 respirator but hey! automobile engines don't need N-95...
 
I've used the factory style air filters that come with the dry foam pre-filter on them (Purolator on the Cummins powered Ram, Baldwin on the 6.2 IDI, and Puro on the 7.3 IDI), only thing I've seen is the restriction gauge gets pulled in somewhat when they're used.
 
Thanks for the input, guys. I'm interested to see how it will turn out. Fun to experiment.
 
AC Delco used to sell "heavy duty" versions of popular filter sizes with an oiled foam outer wrapper. They are very effective at increasing the life of the paper element. Most have been discontiued, I guess due to low demand. One that is still available is the A477c, which replaces the A348c, used on most older Chevy V-8's. I clean the foam on my El Camino every 10,000 miles or so, and after 30,000 miles, the paper still looks almost new.
 
VW used to have a 'snow screen' in the intake tube of early model TDIs which would routinely get clogged with bugs and sand. Most knowledgeable owners would pull the tube and yank out the screen.

Since then, VW eliminated it and released a 'cold climate' version of the air filter which has a foam layer over the paper, exactly as you described. These are excellent filters and I have installed them in every TDI I've worked on.
 
Not a bad idea for extending life of the filter because you can easily and safely pull the sock off and clean it but you'll have to be after it a lot because foam generally has a low capacity. It will also likely increase restriction.

If you wouldn't mind, do a before install and after install restriction reading, resetting the gauge each time and using the same method of getting the reading (i.e a 20-70, full bore acceleration). Please share the results. ( : < )
 
Originally Posted By: Jim Allen
If you wouldn't mind, do a before install and after install restriction reading, resetting the gauge each time and using the same method of getting the reading (i.e a 20-70, full bore acceleration).


This is an excellent idea and would allow you to quantify any additional restriction by the foam prefilter.

Folks on TDIClub found that the foam equipped filter (Mann C37153/1) showed no restriction over the non-foamed filter and lasted a very long time in service (80k miles?) before tripping a restriction meter. Excellent filtration as well.
 
Foam pre-filter is easier to use on a cone type filter, not so easy to use on a flat panel filter.

I use free discarded pantyhose as pre-filter, I have it on the intake tube in front of the air box. I either clean it or replace it once a year, it catches bugs, leave, sand and dust too. The dirty side of the filter itself looks very clean after 30-40k miles.
 
I've thought about this too in the past (a supplemental foam filter wrap), but suspect it's not worth the effort. My guess is it'd tend to be well-filtering, but would reduce the measurable air flow. Or it might tend to restrict only modestly, but accomplish little in the way of filtration. Others have commented on factory foam over-wraps, but those have been designed and flow-tested to work efficiently as a package.

Kinda off-topic, but reading about Mt. Saint Helens erupting in 1980, the emergency response vehicles around the area were driving through thick clouds of abrasive volcanic dust (photos below). I've wondered in the past, how would one deal with that? And the thoughts of an improvised pre-filter swirled around in my Beavis brain. The last photo link is PRECISELY what you want to install on your ride....do it TODAY.
http://inapcache.boston.com/universal/site_graphics/blogs/bigpicture/msh30_05_18/m35_23389317.jpg
http://media.spokesman.com/photos/2010/0...fb4f89a6dc66ee3
http://www.flickr.com/photos/kdavidclark/6072392325/
 
Foam filters are not very restrictive, the important thing is to use proper foam filter oil to treat them. The don't filter very well with out the right oil. Foam filter oil is so tacky you could make home made sticky traps out of it.
 
Originally Posted By: tightwad
AC Delco used to sell "heavy duty" versions of popular filter sizes with an oiled foam outer wrapper. They are very effective at increasing the life of the paper element. Most have been discontiued, I guess due to low demand. One that is still available is the A477c, which replaces the A348c, used on most older Chevy V-8's. I clean the foam on my El Camino every 10,000 miles or so, and after 30,000 miles, the paper still looks almost new.


I remember seeing them sometimes coming on even new pickups a long time ago in the 80's with carbureted engines.
 
What kind of foam do you guys recommend? I bought some crummy A/C foam and realized it's too porous to do much good. I'm thinking some 65 PPI stuff from Uni along with their house-brand filter oil?

Looking at my air filter element, the first step is that I will need to build a little frame to hold the foam onto the inlet side of the filter element.

Just FYI, I have a restriction gauge (Wix air filter monitor) on the engine side of the air box. The filter has never been restrictive enough to make it register anything.
 
JZiggy: Does your restriction gauge measure actual restriction in kPa or In H20 on a scale, or just Green/Yellow/Red. The GYR types vary according to engine, with diesels set to go to yellow at about 20" h2O and and to Red at 25 or 30". Gas units often go to yellow at 10-12" and to red at 15". This is not absolute, just an observation from where I could find the info.

The 65PPI sounds about right but I would hesitate with the oil. If you oil the foam, it will migrate to your primary filter. That might or might not be OK, depending on the filter.
 
Thanks for the input, Jim. I will take a look at it closer. I believe there is a plunger with actual pressure readings.

I always thought oiled foam was a better filter than unoiled. Perhaps in this case it doesn't count for much.
 
It is recommended to oil the filter and let it rest over night before installing it. Foam filter oil is thick and tacky enough it shouldn't contaminate the paper filter as long as the filters are not touching. Just don't over oil it and be sure to squeeze out the excess.
 
The volcanic ash from Mt. St. Helens was both very abrasive and very fine. I remember seeing state patrol cars with a large truck air filter mounted ahead of the grille. There were lots of home-brew ideas...panty hose around the air cleaner was one. Some even remembered to filter the air vent on the differential, for example. The ash got into everywhere and caused wear. It also was fertile and improved soil fertility. Some of the flowering plants put out different color flowers due to the change in the soil's mineral content.

I'm in agreement with the others on the foam pre-filter. Not worth the bother unless you're in a dusty situation. The tacky filter oil makes it work much better.
 
I'm not sure even an oiled foamed prefilter has higher efficiency or adds efficiency to a paper filter. It might extend the life of the paper filter, but with the added cost of the prefilter and time cleaning and reoiling, just as well change the main filter when and if it becomes too dirty or restricted. And if you don;t oil the foam filter it probably does next to nothing.
 
Here's a brief writeup on the air filter install.

Figure 1 - empty air box (fresh air inlet side)
Filter001.jpg


Figure 2 - Aluminum frame that supports the foam element
Filter002.jpg


Figure 3 - Oiled foam element in place. I went with some 60PPI UNI foam using UNI brand filter oil (this stuff is sticky!). The element is 3/8" thick. I opted to put it in directly because it is lightly oiled and I doubt much will transfer to the paper element.
Filter003.jpg


Figure 4 - New NAPA gold air filter goes on top and compresses the perimeter of the foam. The foam and frame are recessed enough to allow the gasket of the air filter to make good sealing contact. Some silicone grease is added to the engine side to help the sealing.
Filter004.jpg


Figure 5 - Air filter restriction gauge taps into the engine side of the filter. After I have driven the car around some (and gotten into full throttle at high RPMs) I will check if the gauge registers anything. So far it has always read no restriction.
Filter005.jpg
 
Status
Not open for further replies.
Back
Top