Yeah, I doubt it restricts the oil flow at all (or is so small you'd never really see it) when fully opened. From what Gary mentioned earlier, it sounds like it's just a check valve to prevent any oil from leaking down the center tube when the engine is turned off. Think of it as a filter with two "ADBVs" in it. Must be some kind of "Porsche spec" (?). Porsche must have asked Purolator to design that filter that way ... first time I've seen or even heard of an ADBV in the center tube of the filter.
Originally Posted By: chunky
It's a spring loaded valve. I cut the filter in half and it takes almost no force to open the valve. It's still a bit of a concern for me as the valve appears to bottleneck flow a good bit. Whether it's more restrictive to flow than the engine, I couldn't tell ya. However, I'd rather use a filter that's more similar in construction to the OEM Honda filter construction.