Greenman, here is the deal if you don't already understand it. Full flow filtration is where the oil flow is completely interrupted from the oil galley passage, directed to a filter, filtered, and then put right back into the oil galley on the other side of the interruption (so to speak). Our beloved early style motors do not have the ability to be full flow (except for some 58-62 261 USA truck motors) without modifying the block (an endeavor that really should only be considered if you are working with a bare block) . Our motors do, however, have the ability to filter oil through what is called a bypass oil filtration system. What that means is that a small amount of oil is bleed off from the oil galley, bypassed so to speak, sent to a filter, filtered and then dumped directly into the pan where the now clean oil is instantly diluted by the dirty oil in the pan. There is no direct interruption of the oil flow in this system, just bleed a little off, filter it and dump back into the pan.
The rub is that by filtering oil this way, you lose oil pressure. So to solve that issue, GM figured out what size restriction in the bypass system would allow oil to flow without killing the oil pressure to the motor. Turns out, 1/16 was about right so the id of the flexible oil lines that feed the bypass oil filter are about 1/16. So, no matter how you wish to do your filter, you have to restrict the oil flow somewhere along the line to about 1/16 or you risk bleeding too much oil and pressure from the motor (resulting in insufficient oil and pressure to the bearings, cam, rockers etc.)
For a good many years I ran a remote spin on Fram PH8A filter with reducer bushings and 1/16 id fittings for the lines I was using. I was using the remote spin on only because I had a dual carb manifold and could not/did not want to mount a canister type filter on the vintage aluminum manifold. That being said, the canister filters are better, at least in my opinion, because they are a little more loosely packed then a spin on (presumably because the spin ons are designed for much higher pressures) and allow the oil to flow past the filtering media a little easier.
All of the above being said, oil filters on our motors were optional, not standard equipment. You could order one as an option, or have one installed by the dealer, or for many many years, all of the major filter manufactures had after market retro kits that you installed either at home or by your local mechanic.
Now, millions of these motors ran and ran and ran without a filter ever. In my view, and I know its not the view of everyone, the bypass system is not really all that effective given the small lines (it will only catch what can pass through the lines) and the fact that it simply dumps the oil into the pan. Given that most of us, at least I think most of us anyway, are no longer driving the trucks as everyday vehicles, you could skip the filter and simply change your oil more often (if you already don't do that now). The 261 that I finished up about the middle of 2015 is the most modified I have done. Its street driven with 1951 302 GMC rods, cut down bearings, Schneider cam, venolia forged pop up pistons, vertex magneto, bigger valves, dual 38 mm webers. Runs great and I run it with no filter. With work and family, I am generally only able to get no more then 500-1500 miles on that motor per year and I change the oil once a year. Three years later, the insides of the motor is still clean as a whistle given the regular oil changes. So you have some options, some more expensive then others but in all events, do keep in mind the need for that 1/16 restriction if you are going to install a filter of any kind..
Just asking, is anyone bringing their 55-57 chevy truck to the trifive nationals in Kentucky next week?
Last edited by Dragsix; 08/03/2018 1:38 PM.
