Bob Delbridge posted:I think I got this data from one of the Mainline Modeler magazines:
Phase IV..August 1948 to February 1949 same as Phase III with a fabricated horizontal stainless steel grill covering the upper course; two portholes with four horizontally slotted air filters sets between them; These were equipped with F7 traction motors and are sometimes referred to as F5's.
Bob, Per a couple of sources I have it looks like the first Phase IV engines still had the D17 traction motors when they came out in Aug '48. In Oct '48 they got the D27 motors and became the "F5". I don't think there is any external difference between the Phase IV and F5.