The original MD
-80s were delivered with JT8D-209s. However, it wasn't too long into the airplane's production run that they were delivered with the D-217s. All of the JT8D-209s were subsequently converted to D-217s. The change required a shop visit to replace the turbines. The most significant change was installation of the air cooled HPT, although the LPT was also replaced to restagger the airfoils for the higher thrust levels. The -217, -217A, and -217C all have the same thrust rating. THe -217C and -219 are in fact the same engine, but have a reversible data plate so an operator can use the higher thrust rating of the D-219 with an adjustment to the fuel control. As FBU
pointed out, there is a charge to use the higher thrust rating. It is interesting to note that the later stages of the LPC
and the entire HPC on the Green Weenies are common with the basic JT8D. Although the parts could be physically interchangeble, they have different LCF lives and thus have different part numbers to keep them separate for life tracking.
BR715, there never was a JT8D-218 engine. At the time the engine proposal was being developed for the 717, which at that time was known as an MD
-95, the engine designation within P&W was a JT8D-290.
And BR715, fuel is the only thing that keeps an engine turning. No fuel, no power. Electric starters are not used on transports like the 717 and larger as it would draw too much current. Air-driven starters that are attached to the gearbox that drive the HPC are used to start the engines. About 2/3s to 3/4s of the energy released in the combustor is used solely to drive the turbines to turn the fan and compressors and the remainder is thrust.