What year Neon does your girlfriends sister have? The transmission going into the SRT is going to be a completley new one from the ones that went into Neons of the past. It is, however, the same company making it. The engine itself is something completely different than what has been in the Neons of the past as well. The engine in the SRT is a V4 2.4L as opposed to the 2L's of previous Neons. On top of that, this car will still be under the 7 year 100,000 mile warranty they have....even with the aftermarket add-on's from Mopar.
