Oil filters

The stock oil filter on the SHO V-6 is the Motorcraft FL-400A. The Fram equivalent is the PH3600. Some SHO owners use the more expensive and difficult-to-find (especially if the rumors of Fram's discontinuation of the HP-1 are true) Fram HP-1, which appears to be just a larger filter. Here's what one SHO owner found when he compared the two filters with help from the Fram technical department:

Oil Filter Comparison: Fram PH3600 and HP-1
Characteristic PH3600 HP-1
Diameter 3" 3 5/8"
Length   Longer
Anti-drainback and relief valves Yes Yes
Size of particles trapped 15 microns 20 microns
Max pressure 250-300 psi 500 psi
Flow rate   Higher
 From this data, it is logical to conclude that there is no advantage to using a HP1 on a SHO unless your engine is modified with a high capacity oil pump and has much higher than stock oil pressure. The PH3600 appears to filters better in a stock engine and costs alot less. Appearances aren't always what they seem, though. As one of the users of the HP-1, this data piqued Gary Morrell's interest, and he called an engineer at Fram's Design Engineering Group. This group frequently works with Ford Motorsports on racing programs. Here's the rest of the story in Gary's words:

Oil filters are tested to SAE J-608, which is a battery of standardized tests that looks at, among other things, a filter's pressure drop -vs- flow, relief valve cracking pressure, relief valve flow characteristics, and the Single Pass Filtering Efficiency (SPFE).

The PH3600 is rated at >90% SPFE for beads of 10 to 20 microns ( a micron is 3.937 X 10^-5 inches, or 0.00003937" ). In other words, it will trap >90% of 10 to 20 micron particles with only one pass thru the filter. The HP-1 and the PH3600 use the same filtering media, the HP-1 just has considerably more media area. The HP-1 is slightly less efficient at trapping small particles because it's SPFE was tested at a higher flow rate than the PH3600. As the flow rate increases, the fluid face velocity at the filter media increases, making it more difficult to trap fine particles.

One could see how a filter manufacturer could play games with the SPFE numbers, and according to Fram, they do. Obviously, any good oil filter is capable of catching 5 micron particles, but the SPFE might be <20% for particles this size. Without the SPFE percentage, claiming that your filter will catch sub-atomic particles is advertising hype. BTW, small particle SPFE improves as the filter gets dirty because the larger passages get plugged, forcing the fluid thru the remaining smaller passages, so a dirty filter coud test more efficient then a new one. SAE J-608 specifies that a new filter is used.

The PH3600 is rated 15 microns SPFE at 3 GPM, the relief valve opens at 6 to 12 psi. At 9 to 12 psi, the relief valve will flow 0.1 GPM, at 15 to 17 psi, the relief valve will flow 3 GPM maximum, due to its orifice size. Fram has not tested the pressure drop-vs-flow beyond 3 GPM, but the pressure drop is <2psi at 3 GPM.

The HP-1 is rated 20 microns SPFE at 10 GPM, the relief valve opens at 9 to 12 psi. The relief valve characteristics are similar to the PH3600. HP-1 pressure drop-vs-flow data:

( if you plot these points, its very linear )

All this gets a bit more interesting when you plug the SHO's stock oil pump flow rates and pressures into the equation, read on...

The Yamaha is a high clearance engine, bearing-wise. It relies on a high volume of oil at moderate pressure to lubricate and cool the bearings. The oil pump is rated to deliver 12.1 GPM @ 43 psi at 6400 RPM crank, which, BTW, is the entire 5 quart oil sump every 10 seconds. The maximum oil pressure that the pump can develop is 57 psi +/-5 psi.

Frankly, I'm a little nervous stuffing 12 GPM thru a filter that's only been tested to 3 GPM.

Ford's spec for the oil filter is 10 GPM with a relief valve rating of 21.5 to 28.5 psi. This means that the filter could conceivably drop some 28 psi before the relief valve opened. That represents a 50% loss of the nominal oil pressure that the pump can deliver. When I mentioned this to the Fram engineer, he was, to put it mildly, amazed. A 50% pressure drop at the filter means that 50% less oil is getting to the bearings. This also makes me nervous.

I studied the benefits and detriments in switching from the PH3600 to the HP-1 and decided that sacrificing a small bit of filtering efficiency was well worth getting more oil to the bearings. I also asked the Fram engineer if I had made a good choice in switching, and in light of the flow rates we had discussed, he was in complete agreement. His feeling is that the PH3600 is in full bypass at 12 GPM, assuming it can flow that rate at all without becoming a complete cork, but, the PH3600 has never been tested to that degree, so we really don't know.

In summary, the biggest hassle I have with many aftermarket oil filters is that they haven't been tested beyond 3 GPM. The HP-1 has, and that's why I use it, and recommend it.

The only other way around the pressure drop situation is a bypass oil filter. These work by diverting a portion of the oil pump's output thru a very fine filter, typically <5 microns, while the majority of the oil goes directly to the engine. If you tried to ram all the oil flow thru a <5 micron filter, the pressure drop would be excessive, unless the filter had enormous surface area. Amsoil has a very nice bypass system, so does System 1.


Fram has just released an expanded line of racing oil filters that have all been tested to at least 10 GPM. The HP-10, which replaces the stock PH3600 filter, looks just like the PH3600, so it will fit on an automatic SHO (the HP-1 does not). However, because it's a high flow filter, the ATX SHO fanatics won't have to worry about oil starvation at the higher (where all SHOs like to be) RPM ranges. The new line of filters was released April 1, so they might not be in stores yet.

Other aftermarket oil filter options (with SHOtimes subscriber comments included) include :