Got this back from K&N...
Thank you for your interest in K&N products. The By-pass valve engages at 14.5 PSI. If you have any further questions please reply to this email or contact customer service at 1-800-858-3333.
Thanks for writing,
Product Specialist – ext. 4082
K&N Engineering Inc.
Jondog, here is an explanation of bypass rating and why it matters...
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 valve
The 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:
'04 Nicky Hayden
Flapper/PAIR Mod-Ladybird Full Ti Moto-GP -w- Long Cans-Proton Flushmount LEDs
HotBodies Undertail-Tyga CF Hugger-HEL Lines
Custom plate mount w integrated LED brake light
15/41 gearing-PCIII USB-Speedohealer-Carbone Lorraine Pads
Spencer Seat mod-Ceramic dual coat headers
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Last edited by TNRC51; 01-16-2014 at 07:12 AM.