Oil filters, and their selection, can be a mystery to us since we are not able to see how or how well they are working without getting very dirty, hooking up a bunch of instruments, and doing extensive testing on both the filter and the oil. Understanding how the oil filter works with the oil pump to provide the engine with an adequate oil pressure of relatively clean oil at all times is the first step in knowing what filter to use. Most importantly, it is more important to have the correct oil pressure and flow through the engine at all times than having the cleanest oil possible. Motorcycles use what is called a full-flow oil system. Assuming that the oil pump is properly spec'd to exceed the needs of the engine at any given rpm, the oil filter must clean the oil without interfering too much with the oil pressure and flow. Since the filter works by forcing the oil through a filtering medium, some measure must be taken to ensure that the pressure loss in the filter does not exceed what margin the oil pump has over the pressure and flow requirements of the engine. This is where the bypass valve in the oil filter comes in. If the pressure between the engine and the filter ever drops below the pressure between the pump and the filter by an amount over the PSI setting of the bypass valve, then the valve opens, allowing oil to bypass the filtering system, and balancing the oil pressures. Since motorcycles tend to be very high performance machines that get driven very aggressively, have very little flywheel effect, have the smallest oil pumps allowable, and rely only on oil pressure for motor bearings, the bypass valve PSI setting tends to be quite low, 8-11psi in most cases, compared to 11-17psi for more robust auto systems. The bypass valve also ensures that engine oil continues to flow, even when the filter has clogged, and during startup when the oil is very viscous compared to how thin it is at running temperature, and that the pressure differential does not destroy the element. Ensuring that the oil filter that you choose not only fits, but has the correct bypass valve setting is very, very important. The best explaination of the oil filter that I have read is by George Nehls. Also, seeRoss Presta's Oil Filter Experiment , another is The Oil Filter Study. LBP - 2-7 PSI, Low Pressure By-Pass Valve
BP - 8-10 PSI
MBP - 11-17 PSI, High Pressure By-Pass Valve
HBP - 18-25 PSI, High Pressure By-Pass Valve
SHBP - 30-45 PSI, Super High Pressure By-Pass Valve
XHBP - 50+ PSI, Extra High Pressure By-Pass Valve AD - Anti-drainback valveThe best cross reference resources online are WIX and Baldwin & FRAM. With regard to filtration, suppose 100 particals of 20 microns were passed through an oil filter and 95 of those were captured in the element. That filter would be rated at 95% efficent @ 20 microns. This is how single pass (SAE J1985) filter ratings work. True industrial filters will be rated at 5, 7, 10, 12, and 20 microns. A filter must be rated for each particulate size under single pass conditions. Remember that the oil in your engine will cycle through the filter countless times during the filters life. Some types of filters may perform better under multi-pass conditions than the single pass numbers would lead you to belive. Some other ways of rating oil filters for multi-pass filtering have been proposed, but none have been standardized that I know of. Three different spin on filters exist for late model Honda sportbikes. They are made by Toyo Roki Mfg. Co., LTD. in Japan. The three filter generally correspond to bikes made in different decades:

*Do not use a race filter for street applications. They are designed for maximum flow, but lack adequate filtration for daily use.
I did my own cut away of the Honda and one of the WIX filters. You can see that HERE. Staying with stock is always safe. They measure 0.685" diameter x 2.782" tall, using a 20x1.5mm (6H) thread. The by-pass valve is set at 8 or 8-11 psi (BP). It also has an anti-drainback valve. Using another filter, even if it fits and looks fine, runs the risk that the bypass valve has a higher setting, possibly starving the motor for oil at times. I would not worry too much about this, but it is worthy of noting. This is a cut away of the Bosch 3323 oil filter. This is one of the best cheap substitutes for stock Honda oil filters that I have looked at. The media is slightly denser than the stock filter, for better filtration, and the filter is longer, helping it flow better.

When deviating from stock it is a good idea to use the largest oil filter that will fit within the confines of the bike and has the same by-pass valve setting. The K&N (auto), Bosch and the Mobil 1 filter are made by Champion Labs and K&N (bike) are made by Hiflofiltro. They are constructed differently, but all well. The K&N (auto) is geared more toward high flow (20microns) while the Mobil 1 is geared toward deeper cleaning (10microns). If money is no object, or your engine is worth more than a new SUV, you could consider the Canton CM Filters Performance Filters. Without any doubt, you should stay away from any oil filter made by Fram. The Filter Manufactures Council is a good source for linking to all filter manufacturers in the US. If you ever need to install an oil cooler of a bypass oil filter, the Flex-Lite sandwich adaptors are the way to go. One important note: Always fill the filter with oil before installing. This is very important. This insures that the oil pressure comes up as soon as possible upon starting. It would be very nice to see an actual test of various filters with regard to their filtering capability rather than their observed construction. but that, we may have to wait for. Many cut apart tests are done by folks like you and me to try to get to the bottom of which filter is better. This may be fine from a quality of construction standpoint, but the only measure for how the filter works with regard to filtration and flow are the SAE J806 & SAE J1858 tests. SAE HS-806 dictate the bypass valve settings.Some people have taken up the task of opening up the oil filters and it is for all of our benefit. Toby Creek writes a nice article about this. Mark Lawrence again has a great write-up on this topic. Russ W. Knize goes nuts about filters as well, but does deal mainly with car filters. Gerhard Bartsch does a similar investigation HERE . Mike Guillory has a general write up on how oil filters work HERE. The Ford SHO Club has a neet look at how a filter works HERE. Fram actually has some great info on rating oil filters HERE and a descriprion of full flow and bypass filtering systems HERE and also a discrition of the vital valves in the lubrication system HERE.One of the best sources for information on oil, greases, and filters online is the Bob is The Oil Guy Forum. Many different opinions and facts are presented, but it is the best place to work out the fine details. Disecting Honda oil filter and good interchanges.