K&P Engineering QR-1 Replacement O-Rings for S1, S2, S5 K&P Oil Filters
- Sold in packs of two
- Each o-ring can be used twice by flipping sides during an oil change
- A 2-pack should last at least up to four oil changes or more
K&P Engineering High Performance Oil Filters
Allow us to offer this primer on filtration.
Filter media has a range of particles that it will remove. The smallest particle size it can
catch is usually referred to the “nominal” size. The largest particle size it lets through is
referred to as the “absolute” size. The sizes between those two are usually expressed as a
beta ratio, or percentage of efficiency. In other words, if you introduce 100 particles of
the 15 micron size and 60 of them get caught, you have a percentage of efficiency of 60.
It is interesting to note that some companies are very liberal with their advertised absolute
There are many different test procedures that can be used to test the particulates a filter
media will remove. There are single pass, multiple pass, SAE, ASTM, and even
European specific tests. What gets difficult is how to compare the numbers used for
marketing filters. Picture yourself standing in the auto parts store in front of a rack of
filters trying to decide which filter is “best”. You see a 22 micron filter with some sort of
efficiency rating attached to it (for example 94% efficiency) and another with a 15
micron number printed on the box with no efficiency rating. And then you see one that
has printed on it that the filter will catch down to 5 microns. There is no way to
accurately compare those numbers. From a marketing standpoint it is better to print
lower numbers since most consumers don’t have a clue about efficiency ratings, and there
is more of a chance of the customer purchasing the lower number filter. Problem is the
“5 micron” filter may be letting more particles through the filter than the one that has 22
microns printed on it. A good example of this is the Harley Davidson Twin Cam filter.
On the box it says it will filter down to 5 microns. When tested at the lab it actually
passes 40 micron particles. Before you condemn the filter, I would note that it pretty
much tied with the Dodge Cummins diesel filter as the tightest OEM filters tested. As an
fyi, most paper filters range from 50 to 90 microns as their absolute number. Ours is 35
(and yes, we can catch 5 micron particles as well).
We use the ASTM test because it offers the smallest amount of manipulation of the
testing process. We test for worst case, or absolute numbers, partially to be able to
compare apples to apples between filters, and partially because of FAA testing.
As filter media gets tighter, the flow rate gets slower and the resistance to flow increases.
This resistance is referred to as differential pressure (the difference in pressure between
the outside and inside of the filter element). As the differential pressure increases, the
pressure against the bypass valve increases and the chance of the bypass opening
K&P Engineering focuses on maximizing flow rates while meeting or exceeding OEM
filtration. Not all stainless steel filter cloth is created equal. We specify the wire
diameter, thread count each direction and the type of weave to use to create our filter
cloth which is how we meet the filtration and flow goals. We can get between 5 and 7
quarts of oil through our filter element in the time it takes to get 1 quart through an OEM
filter element while still meeting or exceeding OEM filtration. The reason for this is that
paper and synthetic filter media is made of fibers that are pressed or glued together and
K&P Engineering High Performance Oil Filters
require a certain thickness to get to the filtration objective. This type of media inherently
has more flow restriction that the filter cloth that K&P Engineering uses. We tested a
pro stock engine on the dyno with a gauge on both sides of the filter cavity. At wide open
throttle we measured 20 lbs of differential pressure on the paper filter (0w at 180
degrees). The K&P Engineering filter measured less than 1 lb. This means the bypass
on the paper filter is open letting unfiltered oil through the filter and into the engine.
Ours has a lot further to go before it opens. The result is more filtered oil getting to the
engine, and getting there faster. The reduction in differential pressure also results in less
back pressure against the oil pump which has the potential to improve performance and or
Some will argue for a very tight filter media, and concentrate on the smallest particles a
filter will catch (even though it might be a nominal number). An analogy we use is to
think about the towel you are about to dry your freshly washed new car with. Are you
more concerned about the dust that has settled on the towel, or the rock that is in the
towel left over from when the towel was dropped. It also becomes a moot point on how
tight the filter media is if the bypass is open and the debris is flowing right past the filter
media. Some filter companies argue that they are ok with the bypass being open because
the debris will eventually get caught as the oil seeps through the media and the oil will
get to a cleaner level at some point in time. Our concern is what damage is being done
while that debris is passing through the engine over and over again waiting to get caught
in the filter media. We have customers that do want to get to that finer level of
cleanliness, and they usually go with a bypass filter setup. They use our filter as primary
filter, and a very tight filter on the bypass circuit. That way the oil is cleaned to OEM
levels with our filter, and as it dribbles through the tighter media of the bypass it will get
The stainless steel filter cloth technology has been around a very long time. It is used in
military aircraft (fighter jets, helicopters) and even used for filtering blood. K&P
Engineering filters are approved by the FAA for aircraft use, and have just recently been
approved by the European equivalent of the FAA (EASA) for use on aircraft in Europe.
We are consistently monitored for quality assurance as a part of these approvals.
Having said all this, K&P Engineering appreciates the people that question the quality
provided by different filters. There are some cheaper counterfeits of our filter out there
that use the K&P Engineering information and numbers to promote themselves. When
we sent the media of those knock off screen filters out for testing at the lab, they came
back as filtering worse than the worst paper filters we have tested. It is kind of like the
Harbor Freight versions of Snap On tools.