Don't remember exactly the suffixes right now but it's for the different cranks.
Basically everything that isn't covered by the O-540 part. Crankshaft and case style, horsepower rating, magneto drive type, fuel pump, accessory case, sump style, etc. The link that Richard5 posted covers it pretty well.
I've seen the tables provided in the link before. The way the tables are laid out requires a bit of sleuthing to derive the answer. Basically, the codes show a series of modifications, including different accessory items. Happy hunting.
Lessee.... E4C5. Same as E4B5, but with 1200 series mags. Therefore, "C" is 1200 series mags. The E4B5 is the same as the E4A5 except again, the mags. E4A5 is same as A4D5 except speed and power rating. Therefore, "E" is probably speed/power rating. Without tracing the direct logic, similar process gives "4" as meaning a different style of crank counterweights, designed for use with Hartzell props, and "5" as meaning one 5th order and 1 6th order counterweight on the crank.
No. It is Opposed. The absence of a "T" is what signifies normally aspirated.
