I have a 1971 240z and I drive up to the mountains frequently but when I go up to the 5000-foot level and higher the engine seems to lack power do to the thinning of the air. For instance, I have to push on the gas more to keep the RPM, it basically feels like a power loss. I have the old stock air intake and was wondering if I had to change it to help the engine breath a bit better. I recently changed the filter but to no avail. I just started restoring this Z and I am a rookie when it comes to engine work. Any help would be much appreciated.