Brendanm's right. On the babbitted motors, the oil filter is on a bypass, and it's only squirting through there at 10 psi (on a good day). And most guys figure only about 10 percent of your oil is getting filtered anyway.
Better and easier is just using the straight 30 weight and changing your oil regularly. It's probably a waste of time to add a filter, but if you want to do it, it's not that hard.
Regards,
John
