had something interesting happen when i changed from flat base filter to drop base. was trying to increase my field of view so thought i would try drop base filter. same size filter 4" x 14", same top.
afr at cruise went from 14.5 up to around 16-1. didn't know if something happened at the track or changing to straight through exhaust did this, so i put the flat base back on and the cruise afr returned to normal. the top i didn't think was very close to the carb inlet but it must have disrupted the airflow somewhat. wot didn't appear to change much that i could tell. anyway, definitely had not expected this. looks like the protrusion lives another day.
here's a picture with the flat base, the drop base was 1.5"-2" lower, same filter & top.
