This modifies the handling of tk0wnz's add-on vehicles to make them a little more realistic (top speed, damage, accleration, suspension) as well as enhancing the performance upgrades, as seen in my Ultimate Driving + EPU mod.

Vehicles Modified:
Pontiac Firebird
Dodge Charger
Spyker
Mercedes-Benz Stirling Moss
Jaguar C-X75
Aston Martin Vulcan
Aston Martin DBS

Requirements:
Open IV
GTA V
tk0wnz vehicle add-on pack

Installation:
1. Open OpenIV and enable edit mode.
2. Navigate to GTA V\update\x64\dlcpacks\tkmods\dlc.rpf\common\data\
3. Drag the two downloaded files here, replacing original.

Credit to tk0wnz for the add-on.