Personally I've never heard of any compatibility issues between any oils and filters, and have never seen any warnings on oil or filter packaging, websites, or spec sheets. By mentioning Fram, I assume you're referring to that line's overall quality, and not any specific compatibility issues with syn oil, correct..?
If you're using syn (or a "diesel" oil) because you desire extended intervals between drains, you might want to consider the following features in a filter:
-Larger media surface area to forstall clogging, or possibly an oversize filter.
-Synthetic (such as Fleetguard StrataPore) or synthetic blended media since additional acids produced over time can supposedly harm paper media.
-Silicone (orange) anti-drainback valve, instead of less durable nitrile (black).
-Open end bypass since extended intervals may allow for more junk to accumulate in the closed end dome (for closed end bypass filters) before bypass eventually occurs. The Motorcraft and Wix filters typically feature open end bypass.
-Teflon-coated or other low-stick mating gaskets.
-Using grease, in lieu of oil, on the mating gasket (although filter manufacturers generally recommend against this due to the potential for leaks).
By the way, the Wix 51334, 51064, and 51568 filters all appear significantly larger than your stock filter (with probably twice the media area for the 51568), and they all share the same thread and gasket. However, I can't vouch for space considerations under the hood, nor thread engagement (whether these filter bases might be more convex or concave than the stock filter). Should you desire, you might do a little experimention at the parts store or visit one of the Miata enthusiasts' sites for more info.
[ November 05, 2003, 05:32 PM: Message edited by: TC ]
