The SRT8 was the model for V8 SRTs when SRT was their own brand. That all changed in May of 2014 when some SRT models were rolled into Dodge and the others discontinued. For 2015-up, SRT became another trim level not a model so no more SRT8s after 2014.
Also, way back in the SRT days, there were multiple vehicles with SRT enhancements and they included the cylinder count to differentiate them a bit.
SRT4 (NEON & Caliber with Turbo - 2.4L 4cyl)
SRT6 (Crossfire with supercharged 3.2L V6)
SRT8 (6.1 then 6.4 HEMI in Charger/Challenger/300/Grand Cherokee)
SRT10 (8L+ V10 in Viper, Ram)
By 2015 only V8s were left (other than the Viper)
SRT8 had 470 HP. They bumped it up to 485 in 2015 for the SRT392. Also some nice stying tweaks, especially on the interior. 2015 was the release of the Hellcat and SRT392 had all the same bells & whistles (except drivetrain of course) including the A8 trans (albeit HP70 and not HP90), bigger brakes, wheels, tires and 3 mode adjustable suspension.