On Mar 24, 2:33 pm, Peter Clark
wrote:

Yea, the stuff after the size tells mechanics about engine and
preinstalled accessory oprions (roller tappets, multiple vaccum pumps,
alternators, etc), most of it is pretty esoteric for the guy pushing
the throttle. You can also run into IO- engines, they have fuel
injection instead of carbs.

O means naturally aspirated, carbureted, opposed, direct drive. IO
means injected opposed direct drive. TSIO means turbocharged injected
opposed direct drive. GTSIO means geared propeller output,
turbocharged, supercharged, injected opposed. GO means geared opposed.
TIGO means turbo'd, injected, geared opposed. Various other
combinations are out there.
Most of the trainers we know are O or IO. A GO engine is rare
now, but was used on the Cessna 175 (GO-300) and the Helio Courier
(GO-480). TIGO and GTSIO engines are found on some Aero Commanders
(680 model?) and the Cessna 421 and the Navajo.
The suffix (like E2D) has lots of meanings, from the engine
mounting arrangement to the accessory case (where things like magnetos
and vacuum pumps and fuel pumps and oil filters and alternators and
starters are mounted), to cylinder base types and so on. Roller cams
are not figured into any of this stuff with the Lycoming; it's a
relatively new development that changes the engine part number only,
not its O- designation, so that the TCDS isn't violated when one is
installed in an airplane that didn't have roller tappets previously.
Dan